The penetrance and variable expression of the Van der Woude syndrome: implications for genetic counseling.

The presence of congenital fistulae in the lower lip in combination with cleft lip, cleft palate, or both is diagnostic of the Van der Woude syndrome. This autosomal dominant syndrome had been reported to have a penetrance of 80% with variable expression. An analysis of eleven families with 67 affected individuals showed variable expression of clefting and lower lip pits. However, penetrance was found to be close to 100%. An approach to counseling advocates advising a 50% chance of inheriting the gene for Van der Woude syndrome.