Otospondylomegaepiphyseal dysplasia (OSMED) is an autosomal recessive skeletal dysplasia accompanied by severe hearing loss. The phenotype overlaps that of the autosomal dominant disorders-Stickler and Marshall syndromes-but can be distinguished by disproportionately short limbs, severe hearing loss, and lack of ocular involvement. In one family with OSMED, a homozygous Gly-->Arg substitution has been described in COL11A2, which codes for the alpha2 chain of type XI collagen. We report seven further families with OSMED. All affected individuals had a remarkably similar phenotype: profound sensorineural hearing loss, skeletal dysplasia with limb shortening and large epiphyses, cleft palate, an extremely flat face, hypoplasia of the mandible, a short nose with anteverted nares, and a flat nasal bridge. We screened affected individuals for mutations in COL11A2 and found different mutations in each family. Individuals from four families, including three with consanguineous parents, were homozygous for mutations. Individuals from three other families, in whom parents were nonconsanguineous, were compound heterozygous. Of the 10 identified mutations, 9 are predicted to cause premature termination of translation, and 1 is predicted to cause an in-frame deletion. We conclude that the OSMED phenotype is highly homogenous and results from homozygosity or compound heterozygosity for COL11A2 mutations, most of which are predicted to cause complete absence of alpha2(XI) chains.

Cleft palate is a common birth defect, but its etiopathogenesis is mostly unknown. Several studies have shown that cleft palate has a strong genetic component. Robin sequence consists of three of the following four findings: micrognathia, glossoptosis, obstructive apnea, and cleft palate. While cleft palate is mainly nonsyndromic, about 80 percent of Robin sequence cases are associated with syndromes. Mutations in genes coding for cartilage collagens II and XI, COL2A1, COL11A1 and COL11A2, have been shown to cause chondrodysplasias that are commonly associated with Robin sequence, micrognathia or cleft palate. We therefore analyzed a cohort of 24 patients with nonsyndromic Robin sequence, 17 with nonsyndromic cleft palate and 21 with nonsyndromic micrognathia for mutations in COL11A2. A total of 23 Robin sequence patients were also analyzed for mutations in COL2A1 and COL11A1. We detected two disease-associated mutations in patients with Robin sequence, an Arg to stop codon mutation in COL11A2 and a splicing mutation in COL11A1. Two putatively disease-associated sequence variations were found in COL11A1 in Robin sequence patients, one in COL11A2 in a patient with micrognathia and one in COL2A1 in two patients with Robin sequence. The results showed that sequence variations in these genes can play a role in the etiology of Robin sequence, cleft palate and micrognathia but are not common causes of these phenotypes.

Early-onset OA demonstrates locus and allelic heterogeneity since the identified variations were in three different collagen genes and each of the six probands had a different mutation. It is also possible that some OA cases represent the mild end of the chondrodysplasia phenotypic spectrum. The major susceptibility alleles in this form of OA, however, remain to be identified.

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