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A designer baby is a baby whose genetic makeup has been selected or altered, often to not include a particular
gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
or to remove genes associated with disease. This process usually involves analysing a wide range of human embryos to identify genes associated with particular
disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
s and characteristics, and selecting embryos that have the desired genetic makeup; a process known as
preimplantation genetic diagnosis Preimplantation genetic diagnosis (PGD or PIGD) is the genetic profiling of embryos prior to implantation (as a form of embryo profiling), and sometimes even of oocytes prior to fertilization. PGD is considered in a similar fashion to prenatal ...
. Screening for single genes is commonly practiced, and polygenic screening is offered by a few companies. Other potential methods by which a baby's genetic information can be altered involve directly editing the genome before birth, which is not routinely performed and only one instance of this is known to have occurred as of 2019, where Chinese twins Lulu and Nana were edited as embryos, causing widespread criticism. Genetically altered embryos can be achieved by introducing the desired genetic material into the embryo itself, or into the sperm and/or egg cells of the parents; either by delivering the desired genes directly into the cell or using the gene-editing technology. This process is known as germline engineering and performing this on embryos that will be brought to term is not typically permitted by law. Editing embryos in this manner means that the genetic changes can be carried down to future generations, and since the technology concerns editing the genes of an unborn baby, it is considered controversial and is subject to ethical debate. While some scientists condone the use of this technology to treat disease, some have raised concerns that this could be translated into using the technology for cosmetic means and enhancement of human traits, with implications for the wider society.


Pre-implantation genetic diagnosis

Pre-implantation genetic diagnosis (PGD or PIGD) is a procedure in which embryos are screened prior to implantation. The technique is used alongside ''in vitro'' fertilisation (IVF) to obtain embryos for evaluation of the genome – alternatively, ovocytes can be screened prior to fertilisation. The technique was first used in 1989. PGD is used primarily to select embryos for implantation in the case of possible genetic defects, allowing identification of mutated or disease-related
alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...
and selection against them. It is especially useful in embryos from parents where one or both carry a
heritable disease A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...
. PGD can also be used to select for embryos of a certain sex, most commonly when a disease is more strongly associated with one sex than the other (as is the case for X-linked disorders which are more common in males, such as
haemophilia Haemophilia, or hemophilia (), is a mostly inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. This results in people bleeding for a longer time after an injury, easy bruising, ...
). Infants born with traits selected following PGD are sometimes considered to be designer babies. One application of PGD is the selection of ' saviour siblings', children who are born to provide a transplant (of an organ or group of cells) to a sibling with a usually life-threatening disease. Saviour siblings are conceived through IVF and then screened using PGD to analyze genetic similarity to the child needing a transplant, to reduce the risk of rejection.


Process

Embryos for PGD are obtained from IVF procedures in which the oocyte is artificially fertilised by sperm. Oocytes from the woman are harvested following
controlled ovarian hyperstimulation Controlled ovarian hyperstimulation is a technique used in assisted reproduction involving the use of fertility medications to induce ovulation by multiple ovarian follicles. These multiple follicles can be taken out by oocyte retrieval (egg col ...
(COH), which involves fertility treatments to induce production of multiple oocytes. After harvesting the oocytes, they are fertilised ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...
'', either during incubation with multiple sperm cells in culture, or ''via''
intracytoplasmic sperm injection Intracytoplasmic sperm injection (ICSI ) is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of em ...
(ICSI), where sperm is directly injected into the oocyte. The resulting embryos are usually cultured for 3–6 days, allowing them to reach the
blastomere In biology, a blastomere is a type of cell produced by cell division (cleavage) of the zygote after fertilization; blastomeres are an essential part of blastula formation, and blastocyst formation in mammals. Human blastomere characteristics In ...
or blastocyst stage. Once embryos reach the desired stage of development, cells are biopsied and genetically screened. The screening procedure varies based on the nature of the disorder being investigated.
Polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...
(PCR) is a process in which DNA sequences are amplified to produce many more copies of the same segment, allowing screening of large samples and identification of specific genes. The process is often used when screening for monogenic disorders, such as cystic fibrosis. Another screening technique, fluorescent ''in situ'' hybridisation (FISH) uses fluorescent probes which specifically bind to highly
complementary sequences : ''For complementary sequences in biology, see complementarity (molecular biology). For integer sequences with complementary sets of members see Lambek–Moser theorem.'' In applied mathematics, complementary sequences (CS) are pairs of sequences ...
on
chromosomes A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
, which can then be identified using
fluorescence microscopy A fluorescence microscope is an optical microscope that uses fluorescence instead of, or in addition to, scattering, reflection, and attenuation or absorption, to study the properties of organic or inorganic substances. "Fluorescence microscop ...
. FISH is often used when screening for chromosomal abnormalities such as
aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...
, making it a useful tool when screening for disorders such as
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
. Following the screening, embryos with the desired trait (or lacking an undesired trait such as a mutation) are transferred into the mother's
uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
, then allowed to develop naturally.


Regulation

PGD regulation is determined by individual countries' governments, with some prohibiting its use entirely, including in
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
, China, and
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
. In many countries, PGD is permitted under very stringent conditions for medical use only, as is the case in
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
, Switzerland,
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
and the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
. Whilst PGD in Italy and Switzerland is only permitted under certain circumstances, there is no clear set of specifications under which PGD can be carried out, and selection of embryos based on sex is not permitted. In France and the UK, regulations are much more detailed, with dedicated agencies setting out framework for PGD. Selection based on sex is permitted under certain circumstances, and genetic disorders for which PGD is permitted are detailed by the countries' respective agencies. In contrast, the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
federal law does not regulate PGD, with no dedicated agencies specifying regulatory framework by which healthcare professionals must abide. Elective sex selection is permitted, accounting for around 9% of all PGD cases in the U.S., as is selection for desired conditions such as
deafness Deafness has varying definitions in cultural and medical contexts. In medical contexts, the meaning of deafness is hearing loss that precludes a person from understanding spoken language, an audiological condition. In this context it is written ...
or dwarfism.


Human germline engineering

Human germline engineering is a process in which the human genome is edited within a
germ cell Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during emb ...
, such as a sperm cell or oocyte (causing heritable changes), or in the
zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...
or embryo following fertilization. Germline engineering results in changes in the genome being incorporated into every cell in the body of the offspring (or of the individual following embryonic germline engineering). This process differs from somatic cell engineering, which does not result in heritable changes. Most human germline editing is performed on individual cells and non-viable embryos, which are destroyed at a very early stage of development. In November 2018, however, a Chinese scientist,
He Jiankui He Jiankui (; ; born 1984) is a Chinese biophysics researcher who was an associate professor in the Department of Biology of the Southern University of Science and Technology (SUSTech) in Shenzhen, China. Earning his Ph.D. from Rice University ...
, announced that he had created the first human germline genetically edited babies. Genetic engineering relies on a knowledge of human genetic information, made possible by research such as the Human Genome Project, which identified the position and function of all the genes in the human genome. As of 2019,
high-throughput sequencing DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...
methods allow
genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing, complete genome sequencing, or entire genome sequencing, is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a ...
to be conducted very rapidly, making the technology widely available to researchers. Germline modification is typically accomplished through techniques which incorporate a new gene into the genome of the embryo or germ cell in a specific location. This can be achieved by introducing the desired DNA directly to the cell for it to be incorporated, or by replacing a gene with one of interest. These techniques can also be used to remove or disrupt unwanted genes, such as ones containing mutated sequences. Whilst germline engineering has mostly been performed in
mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...
and other animals, research on human cells ''in vitro'' is becoming more common. Most commonly used in human cells are germline gene therapy and the engineered nuclease system CRISPR/Cas9.


Germline gene modification

Gene therapy Gene therapy is a medical field which focuses on the genetic modification of cells to produce a therapeutic effect or the treatment of disease by repairing or reconstructing defective genetic material. The first attempt at modifying human DN ...
is the delivery of a nucleic acid (usually DNA or RNA) into a cell as a pharmaceutical agent to treat disease. Most commonly it is carried out using a
vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...
, which transports the nucleic acid (usually DNA encoding a therapeutic gene) into the target cell. A vector can transduce a desired copy of a gene into a specific location to be expressed as required. Alternatively, a transgene can be inserted to deliberately disrupt an unwanted or mutated gene, preventing transcription and
translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
of the faulty gene products to avoid a disease
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
. Gene therapy in patients is typically carried out on somatic cells in order to treat conditions such as some leukaemias and vascular diseases. Human germline gene therapy in contrast is restricted to ''in vitro'' experiments in some countries, whilst others prohibited it entirely, including Australia,
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
and Switzerland. Whilst the
National Institutes of Health The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late ...
in the US does not currently allow ''
in utero ''In Utero'' is the third and final studio album by American rock band Nirvana. It was released on September 21, 1993, by DGC Records. After breaking into the mainstream with their second album, ''Nevermind'' (1991), Nirvana hired Steve Albin ...
'' germline gene transfer clinical trials, ''in vitro'' trials are permitted. The NIH guidelines state that further studies are required regarding the safety of gene transfer protocols before ''in utero'' research is considered, requiring current studies to provide demonstrable efficacy of the techniques in the laboratory. Research of this sort is currently using non-viable embryos to investigate the efficacy of germline gene therapy in treatment of disorders such as inherited
mitochondrial diseases Mitochondrial disease is a group of disorders caused by mitochondrial dysfunction. Mitochondria are the organelles that generate energy for the cell and are found in every cell of the human body except red blood cells. They convert the energy of ...
. Gene transfer to cells is usually by vector delivery. Vectors are typically divided into two classes – viral and non-viral.


Viral vectors

Viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...
infect cells by transducing their genetic material into a host's cell, using the host's cellular machinery to generate viral proteins needed for replication and proliferation. By modifying viruses and loading them with the therapeutic DNA or RNA of interest, it is possible to use these as a vector to provide delivery of the desired gene into the cell. Retroviruses are some of the most commonly used viral vectors, as they not only introduce their genetic material into the host cell, but also copy it into the host's genome. In the context of gene therapy, this allows permanent integration of the gene of interest into the patient's own DNA, providing longer lasting effects. Viral vectors work efficiently and are mostly safe but present with some complications, contributing to the stringency of regulation on gene therapy. Despite partial inactivation of viral vectors in gene therapy research, they can still be
immunogenic Immunogenicity is the ability of a foreign substance, such as an antigen, to provoke an immune response in the body of a human or other animal. It may be wanted or unwanted: * Wanted immunogenicity typically relates to vaccines, where the injectio ...
and elicit an
immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could ...
. This can impede viral delivery of the gene of interest, as well as cause complications for the patient themselves when used clinically, especially in those who already have a serious genetic illness. Another difficulty is the possibility that some viruses will randomly integrate their nucleic acids into the genome, which can interrupt gene function and generate new mutations. This is a significant concern when considering germline gene therapy, due to the potential to generate new mutations in the embryo or offspring.


Non-viral vectors

Non-viral methods of nucleic acid
transfection Transfection is the process of deliberately introducing naked or purified nucleic acids into eukaryotic cells. It may also refer to other methods and cell types, although other terms are often preferred: " transformation" is typically used to des ...
involved injecting a naked DNA plasmid into cell for incorporation into the genome. This method used to be relatively ineffective with low frequency of integration, however, efficiency has since greatly improved, using methods to enhance the delivery of the gene of interest into cells. Furthermore, non-viral vectors are simple to produce on a large scale and are not highly immunogenic. Some non-viral methods are detailed below: *
Electroporation Electroporation, or electropermeabilization, is a microbiology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, electrode arrays or DNA to be introd ...
is a technique in which high voltage pulses are used to carry DNA into the target cell across the
membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...
. The method is believed to function due to the formation of pores across the membrane, but although these are temporary, electroporation results in a high rate of
cell death Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as d ...
which has limited its use. An improved version of this technology, electron-avalanche transfection, has since been developed, which involves shorter (microsecond) high voltage pulses which result in more effective DNA integration and less cellular damage. *The
gene gun In genetic engineering, a gene gun or biolistic particle delivery system is a device used to deliver exogenous DNA (transgenes), RNA, or protein to cells. By coating particles of a heavy metal with a gene of interest and firing these micro-proje ...
is a physical method of DNA transfection, where a DNA plasmid is loaded onto a particle of heavy metal (usually
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
) and loaded onto the 'gun'. The device generates a force to penetrate the cell membrane, allowing the DNA to enter whilst retaining the metal particle. *
Oligonucleotides Oligonucleotides are short DNA or RNA molecules, oligomers, that have a wide range of applications in genetic testing, research, and forensics. Commonly made in the laboratory by solid-phase chemical synthesis, these small bits of nucleic acids ...
are used as chemical vectors for gene therapy, often used to disrupt mutated DNA sequences to prevent their expression. Disruption in this way can be achieved by introduction of small RNA molecules, called
siRNA Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA at first non-coding RNA molecules, typically 20-24 (normally 21) base pairs in length, similar to miRNA, and operating ...
, which signal cellular machinery to cleave the unwanted
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
sequences to prevent their transcription. Another method utilises double-stranded oligonucleotides, which bind
transcription factors In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fun ...
required for transcription of the target gene. By competitively binding these transcription factors, the oligonucleotides can prevent the gene's expression.


ZFNs

Zinc-finger nucleases (ZFNs) are enzymes generated by fusing a zinc finger DNA-binding domain to a DNA-cleavage domain. Zinc finger recognizes between 9 and 18 bases of sequence. Thus by mixing those modules, it becomes easier to target any sequence researchers wish to alter ideally within complex genomes. A ZFN is a
macromolecular A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The ...
complex formed by monomers in which each subunit contains a zinc domain and a FokI endonuclease domain. The FokI domains must dimerize for activities, thus narrowing target area by ensuring that two close DNA-binding events occurs. The resulting cleavage event enables most genome-editing technologies to work. After a break is created, the cell seeks to repair it. * A method is
NHEJ Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology direc ...
, in which the cell polishes the two ends of broken DNA and seals them back together, often producing a frame shift. * An alternative method is homology-directed repairs. The cell tries to fix the damage by using a copy of the sequence as a backup. By supplying their own template, researcher can have the system to insert a desired sequence instead. The success of using ZFNs in gene therapy depends on the insertion of genes to the chromosomal target area without causing damage to the cell. Custom ZFNs offer an option in human cells for gene correction.


TALENs

There is a method called TALENs that targets singular nucleotides. TALENs stand for transcription activator-like effector nucleases. TALENs are made by TAL effector DNA-binding domain to a DNA cleavage domain. All these methods work by as the TALENs are arranged. TALENs are "built from arrays of 33-35 amino acid modules…by assembling those arrays…researchers can target any sequence they like". This event is referred as Repeat Variable Diresidue (RVD). The relationship between the amino acids enables researchers to engineer a specific DNA domain. The TALEN enzymes are designed to remove specific parts of the DNA strands and replace the section; which enables edits to be made. TALENs can be used to edit genomes using
non-homologous end joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology direc ...
(NHEJ) and homology directed repair.


CRISPR/Cas9

The CRISPR/Cas9 system ( CRISPR – Clustered Regularly Interspaced Short Palindromic Repeats, Cas9 – CRISPR-associated protein 9) is a genome editing technology based on the
bacterial Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
antiviral CRISPR/Cas system. The bacterial system has evolved to recognize viral nucleic acid sequences and cut these sequences upon recognition, damaging infecting viruses. The gene editing technology uses a simplified version of this process, manipulating the components of the bacterial system to allow location-specific gene editing. The CRISPR/Cas9 system broadly consists of two major components – the Cas9 nuclease and a
guide RNA A guide RNA (gRNA) is a piece of RNA that functions as a guide for RNA- or DNA-targeting enzymes, with which it forms complexes. Very often these enzymes will delete, insert or otherwise alter the targeted RNA or DNA. They occur naturally, se ...
(gRNA). The gRNA contains a Cas-binding sequence and a ~20
nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecule ...
spacer sequence, which is specific and complementary to the target sequence on the DNA of interest. Editing specificity can therefore be changed by modifying this spacer sequence. Upon system delivery to a cell, Cas9 and the gRNA bind, forming a
ribonucleoprotein Nucleoproteins are proteins conjugated with nucleic acids (either DNA or RNA). Typical nucleoproteins include ribosomes, nucleosomes and viral nucleocapsid proteins. Structures Nucleoproteins tend to be positively charged, facilitating int ...
complex. This causes a conformational change in Cas9, allowing it to cleave DNA if the gRNA spacer sequence binds with sufficient homology to a particular sequence in the host genome. When the gRNA binds to the target sequence, Cas will cleave the
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award' ...
, causing a
double-strand break DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...
(DSB). The resulting DSB can be repaired by one of two mechanisms – *
Non-Homologous End Joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology direc ...
(NHEJ) - an efficient but error-prone mechanism, which often introduces insertions and deletions ( indels) at the DSB site. This means it is often used in knockout experiments to disrupt genes and introduce loss of function mutations. * Homology Directed Repair (HDR) - a less efficient but high-fidelity process which is used to introduce precise modifications into the target sequence. The process requires adding a DNA repair template including a desired sequence, which the cell's machinery uses to repair the DSB, incorporating the sequence of interest into the genome. Since NHEJ is more efficient than HDR, most DSBs will be repaired ''via'' NHEJ, introducing gene knockouts. To increase frequency of HDR, inhibiting genes associated with NHEJ and performing the process in particular
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and sub ...
phases (primarily S and G2) appear effective. CRISPR/Cas9 is an effective way of manipulating the genome ''
in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
'' in animals as well as in human cells ''in vitro'', but some issues with the efficiency of delivery and editing mean that it is not considered safe for use in viable human embryos or the body's germ cells. As well as the higher efficiency of NHEJ making inadvertent knockouts likely, CRISPR can introduce DSBs to unintended parts of the genome, called off-target effects. These arise due to the spacer sequence of the gRNA conferring sufficient sequence homology to random loci in the genome, which can introduce random mutations throughout. If performed in germline cells, mutations could be introduced to all the cells of a developing embryo. There are developments to prevent unintended consequences otherwise known as off-target effects due to gene editing. There is a race to develop new gene editing technologies that prevent off-target effects from occurring with some of the technologies being known as biased off-target detection, and Anti-CRISPR Proteins. For biased off-target effects detection, there are several tools to predict the locations where off-target effects may take place. Within the technology of biased off-target effects detection, there are two main models, Alignment Based Models that involve having the sequences of gRNA being aligned with sequences of genome, after which then the off-target locations are predicted. The second model is known as the Scoring-Based Model where each piece of gRNA is scored for their off-target effects in accordance with their positioning.


Regulation on CRISPR use

In 2015, the International Summit on Human Gene Editing was held in
Washington D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, Na ...
, hosted by scientists from China, the UK and the U.S.. The summit concluded that genome editing of somatic cells using CRISPR and other genome editing tools would be allowed to proceed under FDA regulations, but human germline engineering would not be pursued. In February 2016, scientists at the Francis Crick Institute in
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
were given a license permitting them to edit human embryos using CRISPR to investigate early development. Regulations were imposed to prevent the researchers from implanting the embryos and to ensure experiments were stopped and embryos destroyed after seven days. In November 2018, Chinese scientist
He Jiankui He Jiankui (; ; born 1984) is a Chinese biophysics researcher who was an associate professor in the Department of Biology of the Southern University of Science and Technology (SUSTech) in Shenzhen, China. Earning his Ph.D. from Rice University ...
announced that he had performed the first germline engineering on viable humans embryos, which have since been brought to term. The research claims received significant criticism, and Chinese authorities suspended He's research activity. Following the event, scientists and government bodies have called for more stringent regulations to be imposed on the use of CRISPR technology in embryos, with some calling for a global moratorium on germline genetic engineering. Chinese authorities have announced stricter controls will be imposed, with
Communist Party A communist party is a political party that seeks to realize the socio-economic goals of communism. The term ''communist party'' was popularized by the title of ''The Manifesto of the Communist Party'' (1848) by Karl Marx and Friedrich Engels. ...
general secretary
Xi Jinping Xi Jinping ( ; ; ; born 15 June 1953) is a Chinese politician who has served as the general secretary of the Chinese Communist Party (CCP) and chairman of the Central Military Commission (CMC), and thus as the paramount leader of China, ...
and
government A government is the system or group of people governing an organized community, generally a state. In the case of its broad associative definition, government normally consists of legislature, executive, and judiciary. Government is ...
premier Li Keqiang calling for new gene-editing legislations to be introduced. As of January 2020, germline genetic alterations are prohibited in 24 countries by law and also in 9 other countries by their guidelines. The Council of Europe's Convention on Human Rights and Biomedicine, also known as the Oviedo Convention, has stated in its article 13 "Interventions on the human genome" as follows: "An intervention seeking to modify the human genome may only be undertaken for preventive, diagnostic or therapeutic purposes and only if its aim is not to introduce any modification in the genome of any descendants". Nonetheless, wide public debate has emerged, targeting the fact that the Oviedo Convention Article 13 should be revisited and renewed, especially due to the fact that it was constructed in 1997 and may be out of date, given recent technological advancements in the field of genetic engineering.


Lulu and Nana controversy

The Lulu and Nana controversy refers to the two Chinese twin girls born in November 2018, who had been genetically modified as embryos by the Chinese scientist He Jiankui. The twins are believed to be the first genetically modified babies. The girls' parents had participated in a clinical project run by He, which involved IVF, PGD and genome editing procedures in an attempt to edit the gene
CCR5 C-C chemokine receptor type 5, also known as CCR5 or CD195, is a protein on the surface of white blood cells that is involved in the immune system as it acts as a receptor for chemokines. In humans, the ''CCR5'' gene that encodes the CCR5 p ...
. CCR5 encodes a protein used by
HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
to enter host cells, so by introducing a specific mutation into the gene CCR5 Δ32 He claimed that the process would confer innate resistance to HIV. The project run by He recruited couples wanting children where the man was
HIV-positive The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immun ...
and the woman uninfected. During the project, He performed IVF with sperm and eggs from the couples and then introduced the CCR5 Δ32 mutation into the genomes of the embryos using CRISPR/Cas9. He then used PGD on the edited embryos during which he sequenced biopsied cells to identify whether the mutation had been successfully introduced. He reported some
mosaicism Mosaicism or genetic mosaicism is a condition in multicellular organisms in which a single organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized ...
in the embryos, whereby the mutation had integrated into some cells but not all, suggesting the offspring would not be entirely protected against HIV. He claimed that during the PGD and throughout the pregnancy, foetal DNA was sequenced to check for off-target errors introduced by the CRISPR/Cas9 technology, however the NIH released a statement in which they announced "the possibility of damaging off-target effects has not been satisfactorily explored". The girls were born in early November 2018, and were reported by He to be healthy. His research was conducted in secret until November 2018, when documents were posted on the Chinese clinical trials registry and ''
MIT Technology Review ''MIT Technology Review'' is a bimonthly magazine wholly owned by the Massachusetts Institute of Technology, and editorially independent of the university. It was founded in 1899 as ''The Technology Review'', and was re-launched without "The" in ...
'' published a story about the project. Following this, He was interviewed by the ''
Associated Press The Associated Press (AP) is an American non-profit news agency headquartered in New York City. Founded in 1846, it operates as a cooperative, unincorporated association. It produces news reports that are distributed to its members, U.S. ne ...
'' and presented his work on 27 November and the Second International Human Genome Editing Summit which was held in
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delta i ...
. Although the information available about this experiment is relatively limited, it is deemed that the scientist erred against many ethical, social and moral rules but also China's guidelines and regulations, which prohibited germ-line genetic modifications in human embryos, while conducting this trial. From a technological point of view, the CRISPR/Cas9 technique is one of the most precise and least expensive methods of gene modification to this day, whereas there are still a number of limitations that keep the technique from being labelled as safe and efficient. During the First International Summit on Human Gene Editing in 2015 the participants agreed that a halt must be set on germline genetic alterations in clinical settings unless and until: "(1) the relevant safety and efficacy issues have been resolved, based on appropriate understanding and balancing of risks, potential benefits, and alternatives, and (2) there is broad societal consensus about the appropriateness of the proposed application". However, during the second International Summit in 2018 the topic was once again brought up by stating: "Progress over the last three years and the discussions at the current summit, however, suggest that it is time to define a rigorous, responsible translational pathway toward such trials". Inciting that the ethical and legal aspects should indeed be revisited G. Daley, representative of the summit's management and Dean of Harvard Medical School depicted Dr. He's experiment as "a wrong turn on the right path". The experiment was met with widespread criticism and was very controversial, globally as well as in China. Several
bioethicists Bioethics is both a field of study and professional practice, interested in ethical issues related to health (primarily focused on the human, but also increasingly includes animal ethics), including those emerging from advances in biology, med ...
, researchers and medical professionals have released statements condemning the research, including Nobel laureate
David Baltimore David Baltimore (born March 7, 1938) is an American biologist, university administrator, and 1975 Nobel laureate in Physiology or Medicine. He is President Emeritus and Distinguished Professor of Biology at the California Institute of Technol ...
who deemed the work "irresponsible" and one pioneer of the CRISPR/Cas9 technology, biochemist
Jennifer Doudna Jennifer Anne Doudna (; born February 19, 1964) is an American biochemist who has done pioneering work in CRISPR gene editing, and made other fundamental contributions in biochemistry and genetics. Doudna was one of the first women to share a ...
at
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...
. The director of the NIH, Francis S. Collins stated that the "medical necessity for inactivation of CCR5 in these infants is utterly unconvincing" and condemned He Jiankui and his research team for 'irresponsible work'. Other scientists, including
geneticist A geneticist is a biologist or physician who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a scientist or a lecturer. Geneticists may perform general research on genetic processes ...
George Church of
Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of high ...
suggested gene editing for disease resistance was "justifiable" but expressed reservations regarding the conduct of He's work. The Safe Genes program by DARPA has the goal to protect soldiers against gene editing war tactics. They receive information from ethical experts to better predict and understand future and current potential gene editing issues. The
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...
has launched a global registry to track research on human genome editing, after a call to halt all work on genome editing. The
Chinese Academy of Medical Sciences Peking Union Medical College (), founded in 1906, is a selective public medical college based in Dongcheng, Beijing, China. It is a Chinese Ministry of Education Double First Class University Plan university. The school is tied to the Peking Un ...
responded to the controversy in the journal ''Lancet'', condemning He for violating ethical guidelines documented by the government and emphasising that germline engineering should not be performed for reproductive purposes. The academy ensured they would "issue further operational, technical and ethical guidelines as soon as possible" to impose tighter regulation on human embryo editing.


Ethical considerations

Editing embryos, germ cells and the generation of designer babies is the subject of ethical debate, as a result of the implications in modifying genomic information in a heritable manner. This includes arguments over unbalanced gender selection and gamete selection. Despite regulations set by individual countries' governing bodies, the absence of a standardized regulatory framework leads to frequent discourse in discussion of germline engineering among scientists, ethicists and the general public.
Arthur Caplan Arthur L. Caplan (born 1950) is the Drs. William F. and Virginia Connolly Mitty Professor of Bioethics at New York University Grossman School of Medicine and the founding director of the Division of Medical Ethics. Caplan has made many contribut ...
, the head of the Division of Bioethics at
New York University New York University (NYU) is a private research university in New York City. Chartered in 1831 by the New York State Legislature, NYU was founded by a group of New Yorkers led by then- Secretary of the Treasury Albert Gallatin. In 1832, th ...
suggests that establishing an international group to set guidelines for the topic would greatly benefit global discussion and proposes instating "religious and ethics and legal leaders" to impose well-informed regulations. In many countries, editing embryos and germline modification for reproductive use is illegal. As of 2017, the U.S. restricts the use of germline modification and the procedure is under heavy regulation by the FDA and NIH. The American National Academy of Sciences and
National Academy of Medicine The National Academy of Medicine (NAM), formerly called the Institute of Medicine (IoM) until 2015, is an American nonprofit, non-governmental organization. The National Academy of Medicine is a part of the National Academies of Sciences, Eng ...
indicated they would provide qualified support for human germline editing "for serious conditions under stringent oversight", should safety and efficiency issues be addressed. In 2019, World Health Organization called human germline genome editing as "irresponsible". Since genetic modification poses risk to any
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
, researchers and medical professionals must give the prospect of germline engineering careful consideration. The main ethical concern is that these types of treatments will produce a change that can be passed down to future generations and therefore any error, known or unknown, will also be passed down and will affect the offspring. Some bioethicists, including Ronald Green of
Dartmouth College Dartmouth College (; ) is a private research university in Hanover, New Hampshire. Established in 1769 by Eleazar Wheelock, it is one of the nine colonial colleges chartered before the American Revolution. Although founded to educate Native ...
, raise concern that this could result in the accidental introduction of new diseases in future. When considering support for research into germline engineering, ethicists have often suggested that it can be considered unethical not to consider a technology that could improve the lives of children who would be born with
congenital disorders A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...
. Geneticist George Church claims that he does not expect germline engineering to increase societal disadvantage, and recommends lowering costs and improving education surrounding the topic to dispel these views. He emphasizes that allowing germline engineering in children who would otherwise be born with congenital defects could save around 5% of babies from living with potentially avoidable diseases. Jackie Leach Scully, professor of social and
bioethics Bioethics is both a field of study and professional practice, interested in ethical issues related to health (primarily focused on the human, but also increasingly includes animal ethics), including those emerging from advances in biology, m ...
at Newcastle University, acknowledges that the prospect of designer babies could leave those living with diseases and unable to afford the technology feeling marginalized and without medical support. However, Professor Leach Scully also suggests that germline editing provides the option for parents "to try and secure what they think is the best start in life" and does not believe it should be ruled out. Similarly, Nick Bostrom, an
Oxford Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...
philosopher known for his work on the risks of
artificial intelligence Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech r ...
, proposed that "super-enhanced" individuals could "change the world through their creativity and discoveries, and through innovations that everyone else would use", highlighting not only a personal but societal benefit. Many bioethicists emphasize that germline engineering is usually considered in the best interest of a child, therefore associated should be supported. Dr James Hughes, a bioethicist at
Trinity College, Connecticut Trinity College is a Private university, private Liberal arts colleges in the United States, liberal arts college in Hartford, Connecticut. Founded as Washington College in 1823, it is the second-oldest college in the state of Connecticut. Coed ...
, suggests that the decision may not differ greatly from others made by parents which are well accepted – choosing with whom to have a child and using contraception to denote when a child is conceived. Julian Savulescu, a bioethicist and philosopher at Oxford University believes parents "should allow selection for non‐disease genes even if this maintains or increases social inequality", coining the term ''procreative beneficence'' to describe the idea that the children "expected to have the best life" should be selected. The
Nuffield Council on Bioethics The Nuffield Council on Bioethics is a UK-based independent charitable body, which examines and reports on bioethical issues raised by new advances in biological and medical research. Established in 1991, the Council is funded by the Nuffield Fo ...
said in 2017 that there was "no reason to rule out" changing the DNA of a human embryo if performed in the child's interest, but stressed that this was only provided that it did not contribute to societal inequality. Furthermore, Nuffield Council in 2018 detailed applications, which would preserve equality and benefit humanity, such as elimination of hereditary disorders and adjusting to warmer climate. Philosopher and Director of Bioethics at non-profit Invincible Wellbeing David Pearce argues that "the question f designer babiescomes down to an analysis of risk-reward ratios - and our basic ethical values, themselves shaped by our evolutionary past." According to Pearce,"it's worth recalling that each act of old-fashioned sexual reproduction is itself an untested genetic experiment", often compromising a child's wellbeing and pro-social capacities even if the child grows in a healthy environment. Pearce thinks that as technology matures, more people may find it unacceptable to rely on "genetic roulette of natural selection". Conversely, several concerns have been raised regarding the possibility of generating designer babies, especially concerning the inefficiencies currently presented by the technologies. Bioethicist Ronald Green stated that although the technology was "unavoidably in our future", he foresaw "serious errors and health problems as unknown genetic side effects in 'edited' children" arise. Furthermore, Green warned against the possibility that "the well-to-do" could more easily access the technologies "..that make them even better off". This concern regarding germline editing exacerbating a societal and financial divide is shared amongst other researches, with the chair of the Nuffield Bioethics Council Professor Karen Yeung stressing that if funding of the procedures "were to exacerbate social injustice, in our view that would not be an ethical approach". Social and religious worries also arise over the possibility of editing human embryos. In a survey conducted by the
Pew Research Centre The Pew Research Center is a nonpartisan American think tank (referring to itself as a "fact tank") based in Washington, D.C. It provides information on social issues, public opinion, and demographic trends shaping the United States and the ...
, it was found that only a third of the Americans surveyed who identified as strongly Christian approved of germline editing. Catholic leaders are in the middle ground. This stance is because, according to Catholicism, a baby is a gift from God, and Catholics believe that people are created to be perfect in God's eyes. Thus, altering the genetic makeup of an infant is unnatural. In 1984, Pope John Paul II addressed that genetic manipulation in aiming to heal diseases is acceptable in the Church. He stated that it "will be considered in principle as desirable provided that it tends to the real promotion of the personal well-being of man, without harming his integrity or worsening his life conditions". However, it is unacceptable if designer babies are used to create a super/superior race including cloning humans. The Catholic Church rejects human cloning even if its purpose is to produce organs for therapeutic usage. The Vatican has stated that "The fundamental values connected with the techniques of artificial human procreation are two: the life of the human being called into existence and the special nature of the transmission of human life in marriage". According to them, it violates the dignity of the individual and is morally illicit. A survey conducted by the Mayo Clinic in the Midwestern United States in 2017 saw that most of the participants agreed against the creation of designer babies with some noting its eugenic undertones. The participants also felt that gene editing may have unintended consequences that it may be manifested later in life for those that undergo gene editing. Some that took the survey worried that gene editing may lead to a decrease in the genetic diversity of the population in societies. The survey also noted how the participants were worried about the potential socioeconomic effects designer babies may exacerbate. The authors of the survey noted that the results of the survey showed that there is a greater need for interaction between the public and the scientific community concerning the possible implications and the recommended regulation of gene editing as it was unclear to them how much those that participated knew about gene editing and its effects prior to taking the survey. In Islam, the positive attitude towards genetic engineering is based on the general principle that Islam aims at facilitating human life. However, the negative view comes from the process used to create a Designer baby. Oftentimes, it involves the destruction of some embryos. Muslims believe that "embryos already has a soul" at conception. Thus, the destruction of embryos is against the teaching of the Qur'an, Hadith, and Shari'ah law, that teaches our responsibility to protect human life. To clarify, the procedure would be viewed as "acting like God/Allah". With the idea, that parents could choose the gender of their child, Islam believes that humans have no decision to choose the gender, and that "gender selection is only up to God". In 2020, There has been discussion about American studies that used embryos without embryonic implantation with the CRISPR/Cas9 technique that had been modified with HDR (homology-directed repair) and the conclusions from the results were that gene editing technologies are not mature enough currently for real world use and that there is a need for more studies that generate safe results over a longer period of time. An article in the journal, ''Bioscience Reports,'' discussed how health in terms of genetics is not straightforward and thus there should be extensive deliberation for operations involving gene editing when the technology gets mature enough for real world use where all of the potential effects are known on a case-by-case basis to prevent undesired effects on the subject or patient being operated on. Social aspects also raise concern, as highlighted by Josephine Quintavelle, director of ''Comment on Reproductive Ethics'' at
Queen Mary University of London , mottoeng = With united powers , established = 1785 – The London Hospital Medical College1843 – St Bartholomew's Hospital Medical College1882 – Westfield College1887 – East London College/Queen Mary College , type = Public researc ...
, who states that selecting children's traits is "turning parenthood into an unhealthy model of self-gratification rather than a relationship". One major worry among scientists, including Marcy Darnovsky at the Center for Genetics and Society in
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
, is that permitting germline engineering for correction of disease phenotypes is likely to lead to its use for cosmetic purposes and enhancement. Meanwhile, Henry Greely, a bioethicist at Stanford University in California, states that "almost everything you can accomplish by gene editing, you can accomplish by embryo selection", suggesting the risks undertaken by germline engineering may not be necessary. Alongside this, Greely emphasizes that the beliefs that genetic engineering will lead to enhancement are unfounded, and that claims that we will enhance intelligence and personality are far off – "we just don't know enough and are unlikely to for a long time – or maybe for ever".


See also

*
Biohappiness Biohappiness, or bio-happiness, is the elevation of wellbeing in humans through biological methods, including germline engineering through screening embryos with genes associated with a high level of happiness, or the use of drugs intended to raise ...
* Directed evolution (transhumanism) * Epidemiology of genetic disorder *
Eugenics Eugenics ( ; ) is a fringe set of beliefs and practices that aim to improve the genetic quality of a human population. Historically, eugenicists have attempted to alter human gene pools by excluding people and groups judged to be inferior o ...
*
Eugenics in the United States Eugenics, the set of beliefs and practices which aims at improving the Genetics, genetic quality of the human population, played a significant role in the history and culture of the United States from the late 19th century into the mid-20th c ...
* Genetically modified organism *
Human enhancement Human enhancement (HE) can be described as the natural, artificial, or technological alteration of the human body in order to enhance physical or mental capabilities. Technologies Existing technologies Three forms of human enhancement curre ...
* Human genetic engineering * Human germline engineering * Liberal eugenics * Lulu and Nana (Gene edited babies in China 2018) * Moral enhancement *
Reprogenetics Assisted reproductive technology (ART) includes medical procedures used primarily to address infertility. This subject involves procedures such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), cryopreservation of gametes ...
*
Transhumanism Transhumanism is a philosophical and intellectual movement which advocates the enhancement of the human condition by developing and making widely available sophisticated technologies that can greatly enhance longevity and cognition. Transhuma ...


References


Further reading

* * * * * A non-fiction account of Strongin's pioneering use of IVF and PGD to have a healthy child whose cord blood could save the life of her son Henry {{refend 1989 introductions 2018 introductions Bioethics Emerging technologies Ethically disputed medical practices Fertility medicine Genetic engineering Genome editing Human reproduction Transhumanism