Part II. Amyoplasia: twinning in amyoplasia--a specific type of arthrogryposis with an apparent excess of discordantly affected identical twins.

We report on 11 cases of amyoplasia in one of identical twins. In total, 135 patients with amyoplasia were ascertained from a study of 350 patients with multiple congenital joint contractures (arthrogryposis). These 11 cases of identical twins with amyoplasia represent 8% of our patients with amyoplasia. At least 18 sets of twins with congenital contractures have been reported previously. However, only four of these appear to involve identical twins discordant for amyoplasia. Thus, 15 cases in which only one of identical twins are affected with amyoplasia have been identified.