Recurrent de novo interstitial deletion of 16q in two mentally retarded sisters

Two sisters with similar clinical features are described. Their clinical manifestations include mental retardation, delayed speech development, low percentiles for height, weight and head circumference, dysmorphic ears, cubitus valgus, pseudoclubbing of fingers, flexion deformity of toes, small kidneys, elevated serum creatinine and blood urea nitrogen (BUN). High resolution chromosome analysis revealed a complete deletion of 16qh with a concurrent small deletion of the adjacent euchromatic segment 16q12.1 in one of the no. 16 chromosomes of both sisters, whereas the parents had normal no. 16 chromosomes. Length polymorphism of the 16qh regions appeared to indicate a maternal origin of the deleted no. 16 chromosome in both sisters. The clinical features of both sisters were attributed to the 16q12.1 deletion. Since both parents were cytogenetically normal, the two sisters were considered as a recurrence of a similar de novo interstitial deletion. Possible mechanisms which could lead to recurrence of a seemingly de novo event are discussed.