Risk calculation of autosomal dominant inheritance

In diseases following autosomal dominant inheritance, the disease is manifesting in individuals carrying one allele with the disease-causing mutation, and one normal allele of the gene. These patients are heterozygous for the mutation. When one of the parents is affected by the disease each of their offspring have a 50% risk of inheriting the mutation and the disease. An exception to this rule is in the cases where the disease displays reduced penetrance: this means that individuals carrying the disease-causing mutation do not necessarily develop the disease symptoms, however, they may still pass on the mutation to their offspring, and they may become affected.

Figure 1. A pedigree showing autosomal dominant inheritance.