Charcot-Marie-Tooth disease: data for genetic counseling relating age to risk.

One hundred and nine individuals from complete sibships at risk for autosomal dominant Charcot-Marie-Tooth (CMT) disease in 15 unrelated families were evaluated by physical examination and motor nerve conduction studies. Penetrance of the gene was 28% in the first decade, but was essentially complete by the middle of the third decade. The average age of onset of symptoms was 12.2 y, with a standard deviation of 7.3. Persons at risk who have no clinical manifestations and who are over age 27 have less than a 3% probability of having inherited the CMT gene.