Congenital absence of gluteal muscles. Report of two sibs.

A family is described with the following features: 1) Two propositi, a male and a female, with congenital absence of gluteal muscles and with spina bifida occulta. 2) Both parents and two apparently normal siblings with sacral spina bifida occulta. 3) Two siblings of the propositi who died soon after birth, one with anencephaly and the other with a probable spina bifida. Two alternative hypotheses for the etiology of these malformations are suggested: first, the muscular defect could be caused by an autosomal recessive gene independent of the open neural-tube defects; second, both types of malformations could be due to the same autosomal recessive gene. Then compensatory muscular changes which allow the propositi to walk are discussed.