Diastrophic dysplasia: extreme variability within a sibship.

Three sibs were eventually diagnosed as having diastrophic dysplasia. The firstborn, a male, lacked many of the clinical manifestations and radiological abnormalities of the hands, such that the diagnosis of diastrophic dysplasia could not be made. Subsequently, his twin sisters were born with more severe skeletal involvement, but not many additional clinical findings, until one of his sisters (patient 2) developed a left ear cyst at age 2 months. Some cases of diastrophic dysplasia may be mild enough not to allow for a secure diagnosis, particularly in a neonate or infant occurring as the first affected person in the family.