Non-penetrance in tuberous sclerosis.

As a result of extreme clinical variability in tuberous sclerosis, with one well-documented example of non-penetrance, phenotypically normal siblings or children of patients with tuberous sclerosis are thought to be at increased risk of having children with the disease. We report that the case of apparent non-penetrance that was previously described is the result of two independent tuberous-sclerosis mutations in the same family.