RT Journal Article SR Electronic T1 Variability of expression in tuberous sclerosis. JF Journal of Medical Genetics JO J Med Genet FD BMJ Publishing Group Ltd SP 41 OP 43 DO 10.1136/jmg.30.1.41 VO 30 IS 1 A1 H Northrup A1 J W Wheless A1 T K Bertin A1 R A Lewis YR 1993 UL http://jmg.bmj.com/content/30/1/41.abstract AB We present three families in whom a diagnosis of tuberous sclerosis is difficult to secure and we review published reports about similar cases. Tuberous sclerosis has been reported to affect as many as 1 in 9400 subjects in the population. The manifestations of this disease vary not only between but also within families. Currently no reliable method of prenatal diagnosis is available. For these reasons, subjects known to be at 50% risk should be assessed scrupulously to clarify their status. These cases illustrate the difficulties in the clinical diagnosis of tuberous sclerosis and further reinforce the need for a molecular method of determining whether an at risk subject has the disease.