The type XI collagenopathies.

Type XI collagen is a minor component of cartilage collagen. Mutations of the three genes coding for its proteins are expressed in a peculiar phenotype. Clinical changes include facial anomalies, cleft palate and hearing defects. Ocular changes occur in some disorders. Radiographs show a spectrum of epiphyseal dysplasias with wide metaphyses and spondylar abnormalities. The pattern of clinical and radiographic changes is also found in some type II collagenopathies. On the basis of molecular studies, three type XI collagenopathies have been defined: Stickler syndrome type II, and dominant and recessive oto-spondylo-megaepiphyseal dysplasia (OSMED). Stickler syndrome I and Kniest dysplasia are type II collagenopathies with considerable clinical and radiographic overlap. Inborn errors of cartilage collagen formation lead to a family of genetically heterogeneous but pathogenetically related and hence phenotypically similar disorders. The type XI collagenopathies are part of this family.