The value of investigation for genetic counselling in tuberous sclerosis

Forty sets of parents and 24 sibs of patients with tuberous sclerosis were investigated by an extensive protocol, including clinical examination of skin, hair, and oral cavity, direct and indirect ophthalmoscopy, cranial CT scan, renal ultrasound, and a radiological skeletal survey. None of the clinical examinations provided evidence that any of the subjects was affected. Similarly, the cranial CT scan, renal ultrasound, and skeletal survey failed to identify any occult gene carriers. All of these investigations showed abnormalities in some parents but none was diagnostic. This study shows the difficulties in interpretation that these investigations may produce with consequent problems for genetic counselling. The study does not support the routine use of these tests. There are published reports where the diagnosis of tuberous sclerosis has been made in adults exclusively on a CT scan and an argument can be made for including this investigation. There is no indication for performing renal ultrasound nor skeletal x rays in parents who have normal clinical examinations.