Autosomal dominant inheritance
Eg Huntington disease, most familial cancers
Figure 4
Huntington disease: autosomal dominant inheritance
- When a condition follows an autosomal dominant pattern of inheritance, the family tree will usually reveal
multiple affected members on one side of the family.
- The condition is usually inherited on one side of the family and present down multiple generations.
- Wide variability in clinical expression is common in many autosomal dominant conditions, even within the same family. Severely affected offspring may be born to minimally affected adults and thus careful examination of a child's parents can be important (eg neurofibromatosis type 1 and type 2, see Neurofibromatosis).
- Early onset of conditions such as cancer can be indicative of autosomal dominant inheritance within a family.
- Not all autosomal dominant conditions show 100% penetrance (eg BRCA1 gene mutations; see Cancer in the family). Penetrance describes the extent to which characteristics controlled by the gene, or mutation within the gene, will be expressed. Consequently, people who carry the autosomal dominant mutation may not always develop the condition – this would demonstrate incomplete penetrance. Other genes and lifestyle factors such as diet, exercise and smoking may also affect the onset of some conditions.
- An autosomal dominant condition cannot be ruled out just because there is only one affected family member. Isolated cases of dominant conditions may be the result of a spontaneous (de novo) gene mutation.
- If you notice a family history of a dominant condition, and would like more information on the condition and/or recurrence risks, contact Genetics Services (see Contacts, support and testing).