A genetic disorder
, or genetic disease
is a disease
caused, at least in part, by the genes of the person with the disease. There are a number of possible causes for genetic defects:
- They may be caused by an unwelcome mutation, as are most cancers.
- There are genetic disorders caused by the accidental duplication of a chromosome, as in Down syndrome, or repeated duplication of part of a chromosome as in Fragile X syndrome.
- The defective genes are often inherited from the person's parents. In this case, the genetic disorder is known as a hereditary disease. This can often happen unxpectedly when two healthy carriers of a defective recessive gene reproduce, but can also happen when the defective gene is dominant.
Genetic disorders can frequently be explained as due to the change of a single DNA
base in a gene
, resulting in an enzyme
or other protein
either not being produced, or having altered functionality. This can be trivial and relatively harmless in its effects, such as color blindness
, or lethal such as Tay-Sachs. Other disorders, though harmful to those afflicted with them, appear to offer some advantage to carriers; as in carriers of sickle cell anemia
appearing to have enhanced resistance to malaria
Several hereditary diseases are sex-linked, meaning that they afflict one sex much more common than the other because the mutation is located on the X (or, rarely, on the Y) chromosome.