Inheriting a disease, condition, or trait depends on the type of chromosome affected (autosomal or sex chromosome). It also depends on whether the trait is dominant or recessive.
A single abnormal gene on one of the first 22 nonsex (autosomal) chromosomes from either parent can cause an autosomal disorder.
Dominant inheritance means an abnormal gene from one parent can cause disease, even though the matching gene from the other parent is normal. The abnormal gene dominates.
An autosomal dominant disease can also occur as a new condition in a child when neither parent has the abnormal gene.
A parent with an autosomal dominant condition has a 50% chance of having a child with the condition. This is true for each pregnancy. It means that each child's risk for the disease does not depend on whether their sibling has the disease. Children who do not inherit the abnormal gene will not develop or pass on the disease.
If someone is diagnosed with an autosomal dominant disease, that person's parents should also be tested for the abnormal gene.
Examples of autosomal dominant disorders include Huntington's disease and neurofibromatosis type 1.