Family studies of infantile visceral myopathy: a congenital myopathic pseudo-obstruction syndrome.

Abstract

We conducted family studies of a rare congenital myopathic pseudo-obstruction to provide recurrence risks to families of affected children. This infantile visceral myopathy (IVM) involves the smooth muscles of the digestive tract and frequently the urinary bladder. Family and pregnancy histories from 16 families were evaluated to identify possible environmental or genetic components. The families were ethnically and geographically diverse within the United States. Eleven of the children were alive, four had died, and the status of one was unknown. The sex ratio was 5 females to 11 males. The pregnancy histories provided no evidence of a teratogenic cause. In one family, the disorder passed from parent to child. There were no consanguineous matings, no similarly affected sibs, and except for one case, the family histories did not suggest affected relatives. We suspect a new dominant mutation may be responsible for some cases of IVM, whereas in others, IVM may be caused from a dominant gene with variable expressivity and incomplete penetrance. Therefore, we predict the recurrence risk of severely affected children is much less than the 25 or 50% risk sometimes given families based on the assumption of autosomal recessive or autosomal dominant inheritance. When counseling IVM families, a thorough family history is essential. Subsequent pregnancies should be monitored by ultrasound for megacystis that was detected prenatally in seven of these cases.