A lipid storage disorder (or lipidosis) is any one of a group of inherited

metabolic Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the ...

disorders in which harmful amounts of fats or

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

s accumulate in some body cells and tissues. People with these disorders either do not produce enough of one of the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s needed to metabolize and break down lipids or, they produce enzymes that do not work properly. Over time, the buildup of fats may cause permanent cellular and tissue damage, particularly in the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

spleen The spleen (, from Ancient Greek '' σπλήν'', splḗn) is an organ (biology), organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The spleen plays important roles in reg ...

, and

bone marrow Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...

. Inside cells under normal conditions,

lysosome A lysosome () is a membrane-bound organelle that is found in all mammalian cells, with the exception of red blood cells (erythrocytes). There are normally hundreds of lysosomes in the cytosol, where they function as the cell’s degradation cent ...

s convert, or metabolize, lipids and proteins into smaller components to provide energy for the body.

Classification

Disorders that store this

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

material are part of the lysosomal storage diseases family of disorders.

Sphingolipidoses

Many lipid storage disorders can be classified into the subgroup of sphingolipidoses, as they relate to

sphingolipid Sphingolipids are a class of lipids containing a backbone of sphingoid bases, which are a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extracts in the 1870s and were named after the mythological sp ...

metabolism. Members of this group include Niemann-Pick disease, Fabry disease, Krabbe disease, Gaucher disease,

Tay–Sachs disease Tay–Sachs disease is an Genetic disorder, inherited fatal lysosomal storage disease that results in the destruction of nerve cells in the brain and spinal cord. The most common form is infantile Tay–Sachs disease, which becomes apparent arou ...

, metachromatic leukodystrophy, multiple sulfatase deficiency, and Farber disease. They are generally inherited in an

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

fashion, but Fabry disease is

X-linked Sex linkage describes the sex-specific patterns of inheritance and expression when a gene is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome). Genes situated on the X-chromosome are thus termed X-linked, and ...

. Taken together, sphingolipidoses have an incidence of approximately 1 in 10,000. Enzyme replacement therapy is available mainly to treat Fabry disease and Gaucher disease and people with these types of sphingolipidoses may live well into adulthood. Generally, the other types are fatal by age 1 to 5 years for infantile forms, but progression may be mild for juvenile-onset or adult-onset forms. Alternatively, some of the sphingolipidoses may be classified into either GM1 gangliosidoses or GM2 gangliosidoses.

belongs to the latter.

Other

Other lipid storage disorders that generally are not classified as sphingolipidoses include fucosidosis, Schindler disease, and Wolman disease.

Genetics

Lipid storage diseases can be inherited two ways:

Autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

inheritance occurs when both parents carry and pass on a copy of the faulty gene, but neither parent show signs and symptoms of the condition and is not affected by the disorder. Each child born to these parents have a 25 percent chance of inheriting both copies of the defective gene, a 50 percent chance of being a carrier, and a 25 percent chance of not inheriting either copy of the defective gene. Children of either gender may be affected by an autosomal recessive this pattern of inheritance.

X-linked recessive ''Main Article'': Sex linkage X-linked recessive inheritance is a mode of Mendelian inheritance, inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males (who are necessarily hemizygous for ...

(or sex linked) inheritance occurs when the mother carries the affected gene on the X chromosome that has determined the child's gender and passes it to her son. Sons of carriers have a 50 percent chance of inheriting the disorder. Daughters have a 50 percent chance of inheriting the X-linked chromosome, but usually are not severely affected by the disorder. Affected men do not pass the disorder to their sons, but their daughters will be carriers for the disorder.

Diagnosis

Diagnosis of the lipid storage disorders can be achieved through the use of several tests. These tests include clinical examination, biopsy,

genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

, molecular analysis of cells or tissues, and enzyme assays. Certain forms of this disease also can be diagnosed through urine testing, which detects the stored material.

Prenatal testing Prenatal testing is a tool that can be used to detect some birth defects at various stages prior to birth. Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problem ...

also is available to determine whether the fetus will have the disease or is a carrier.

Treatment

There are no specific treatments for lipid storage disorders; however, there are some highly effective enzyme replacement therapies for people with type 1 Gaucher disease and some patients with type 3 Gaucher disease. There are other treatments such as the prescription of certain drugs such as phenytoin and carbamazepine to treat pain for patients with Fabry disease. Furthermore, gene therapies and bone marrow transplantation may prove to be effective for certain lipid storage disorders. Diet restrictions do not help prevent the buildup of lipids in the tissues because the cells in the tissues synthesize lipids from any precursor readily available (such as amino acids or carbohydrates).

References

External links

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