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 increa sed risk of having children with the disease. We report that the case of ap parent non-penetrance that was previously described is the result of two in dependent tuberous-sclerosis mutations in the same family.