Risk of recurrence

The risk of recurrence for a multifactorial disorder within a
family is generally low and mainly affects first degree relatives.
In many conditions family studies have reported the rate with
which relatives of the index case have been affected. This allows
empirical values for risk of recurrence to be calculated, which
can be used in genetic counselling. Risks are mainly increased
for first degree relatives. Second degree relatives have a slight
increase in risk only and third degree relatives usually have the
same risk as the general population. The severity of the
disorder and the number of affected individuals in the family
also affect recurrence risk. The recurrence risk for bilateral
cleft lip and palate is higher than the recurrence risk for cleft
lip alone, and the recurrence risk for neural tube defect is 4%
after one affected child, but 12% after two. Some conditions
are more common in one sex than the other. In these disorders
the risk of recurrence is higher if the disorder has affected the
less frequently affected sex. As with the other examples, the
greater genetic susceptibility in the index case confers a higher
risk to relatives. A rational approach to preventing
multifactorial disease is to modify known environmental
triggers in genetically susceptible subjects. Folic acid
supplementation in pregnancies at increased risk of neural
tube defects and modifying diet and smoking habits in
coronary heart disease are examples of effective intervention,
but this approach is not currently possible for many disorders.