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

We conducted family studies of a rare congenital myopathic pseudo-obstructi on to provide recurrence risks to families of affected children. This infan tile visceral myopathy (IVM) involves the smooth muscles of the digestive t ract and frequently the urinary bladder. Family and pregnancy histories fro m 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 th e status of one was unknown. The sex ratio was 5 females to 11 males. The p regnancy histories provided no evidence of a teratogenic cause. In one fami ly, the disorder passed from parent to child. There mere no consanguineous matings, no similarly affected sibs, and except for one case, the family hi stories did not suggest affected relatives. We suspect a new dominant mutat ion may be responsible for some cases of IVM, whereas in others, IVM may be caused from a dominant gene with variable expressivity and incomplete pene trance. Therefore, me predict the recurrence risk of severely affected chil dren is much less than the 25 or 50% risk sometimes given families based on the assumption of autosomal recessive or autosomal dominant inheritance. W hen counseling IVM families, a thorough family history is essential. Subseq uent pregnancies should be monitored by ultrasound for megacystis that was detected prenatally in seven of these cases. (C) 1999 Wiley-Liss, Inc.