Genetic disorder

A genetic disorder, or genetic disease is a disease caused by abnormal expression of one or more genes in a person causing a clinical phenotype. There are a number of possible causes for genetic defects:

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• They may be caused by a mutation in a gene, effecting its function.
• There are genetic disorders caused by the abnormal chromosome number, as in Down syndrome (extra chromosome 21) and Klinefelter's syndrome (a male with 2 X chromosomes).
• Triplet expansion repeat mutations can cause Fragile X syndrome or Huntington's disease, by modification of gene expression or gain of function, respectively.
• Defective genes are often inherited from the parents. In this case, the genetic disorder is known as a hereditary disease. This can often happen unexpectedly when two healthy carriers of a defective recessive gene reproduce, but can also happen when the defective gene is dominant.

Currently around 4,000 genetic disorders are known; new ones are constantly discovered. The vast majority of these disorders are quite rare, and affect one person in every several thousands or millions. Cystic fibrosis is the most common genetic disorder; around 5% of the population of the United States carry the defective gene.

Related Topics:
Cystic fibrosis - United States

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Genetic disorder: Single gene disorders ►