Genetic disorder

Genetic disorder
A boy with Down syndrome, one of the most common genetic disorders
Specialty	Medical genetics

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 are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome.^[1][2] The mutation responsible can occur spontaneously before embryonic development (a de novo mutation), or it can be inherited from two parents who are carriers of a faulty gene (autosomal recessive inheritance) or from a parent with the disorder (autosomal dominant inheritance). When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA (due to their size).^[3]

There are well over 6,000 known genetic disorders,^[4] and new genetic disorders are constantly being described in medical literature.^[5] More than 600 genetic disorders are treatable.^[6] Around 1 in 50 people are affected by a known single-gene disorder, while around 1 in 263 are affected by a chromosomal disorder.^[7] Around 65% of people have some kind of health problem as a result of congenital genetic mutations.^[7] Due to the significantly large number of genetic disorders, approximately 1 in 21 people are affected by a genetic disorder classified as "rare" (usually defined as affecting less than 1 in 2,000 people). Most genetic disorders are rare in themselves.^[5][8]

Genetic disorders are present before birth, and some genetic disorders produce birth defects, but birth defects can also be developmental rather than hereditary. The opposite of a hereditary disease is an acquired disease. Most cancers, although they involve genetic mutations to a small proportion of cells in the body, are acquired diseases. Some cancer syndromes, however, such as BRCA mutations, are hereditary genetic disorders.^[9]