The common disease-common variant (often abbreviated CD-CV) hypothesis predicts that common disease-causing

allele 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 ...

s, or

variants Variant may refer to: In arts and entertainment * ''Variant'' (magazine), a former British cultural magazine * Variant cover, an issue of comic books with varying cover art * ''Variant'' (novel), a novel by Robison Wells * "The Variant", 2021 e ...

, will be found in all human populations which manifest a given disease. Common variants (not necessarily disease-causing) are known to exist in coding and regulatory sequences of genes. According to the CD-CV hypothesis, some of those variants lead to susceptibility to complex polygenic diseases. Each variant at each gene influencing a complex disease will have a small additive or multiplicative effect on the disease phenotype. These diseases, or traits, are evolutionarily neutral in part because so many genes influence the traits. The hypothesis has held in the case of putative causal variants in

apolipoprotein Apolipoproteins are proteins that bind lipids (oil-soluble substances such as fats, cholesterol and fat soluble vitamins) to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph. The lipid components of lipoproteins ...

E, including ''APOE'' ε4, associated with

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...

.Expanded high-resolution genetic study of 109 Swedish families with Alzheimer's disease, Anna Sillén, Jorge Andrade, Lena Lilius, Charlotte Forsell, Karin Axelman, Jacob Odeberg, Bengt Winblad and Caroline Graff, European Journal of Human Genetics (2008) 16, 202–208; ; published online 24 October 2007

IL23R The interleukin-23 receptor is a type I cytokine receptor. It is encoded in human by the ''IL23R'' gene. In complex with the interleukin-12 receptor β1 subunit ( IL-12Rβ1), it is activated by the cytokine interleukin 23 (IL-23). The ''IL23R'' m ...

has been found to be associated with

Crohn's disease Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any segment of the gastrointestinal tract. Symptoms often include abdominal pain, diarrhea (which may be bloody if inflammation is severe), fever, abdominal distensi ...

; the at-risk allele has a frequency 93% in the general population . One common form of variation across human genomes is called a

single nucleotide polymorphism In genetics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently larg ...

(SNP). As indicated by the name, SNPs are single base changes in the DNA. SNP variants tend to be common in different human populations. These polymorphisms have been valuable as genomic signposts, or "markers", in the search for common variants that influence susceptibility to common diseases. Research has linked common SNPs to diseases such as type 2 diabetes, Alzheimer's,

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social w ...

and

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high b ...

References

{{reflist, 35em Human genetics Statistical genetics Race and health

See also

References