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Otospondylomegaepiphyseal dysplasia (OSMED) is an inborn error of cartilage collagen formation characterized by sensorineural hearing loss, enlarged epiphyses, skeletal dysplasia with disproportionately short limbs, vertebral body anomalies and a characteristic facies.
ORPHA:1427Classification level: Disorder
The prevalence is unknown but less than 30 cases have been described in the literature so far.
Typical facial features include midface hypoplasia, a short nose with anteverted nares and a flat nasal bridge, a long philtrum, cleft palate/bifid uvula, micrognathia, and hypertelorism. Joint pain and restricted mobility of the metacarpophalangeal joints appear during the second decade of life. The sensorineural hearing loss is generally described as moderate and nonprogressive. Early onset of osteoarthritis has also been reported.
OSMED is classed among the type XI collagenopathies as the majority of reported cases have been associated with homozygous mutations in the COL11A2 gene (6p21.3), encoding the alpha2 chain of type XI collagen.
Diagnosis is made on the basis of the clinical phenotype and typical radiographic findings: shortening of the long bones (humerus, radius, ulna, tibia, and fibula) with large epiphyses and metaphyseal flaring, coronal clefting and mild to moderate platyspondyly.
OSMED shows significant clinical overlap with Weissenbacher-Zweymuller syndrome (WZS) and Stickler syndrome (see these terms). Whilst OSMED and Stickler syndrome can be distinguished early in life due to the absence of ocular anomalies in OSMED, differentiation of OSMED and WZS (also associated with heterozygous mutations in the COL11A2 gene) may be more problematic.
OSMED is inherited as an autosomal recessive trait.
Management and treatment
Treatment is symptomatic only, involving closure of the cleft palate, audiometry and adapted management of the hearing loss, and treatment of the joint pain.
The prognosis depends on the severity of the osteoarthritis (which may require early joint replacement), hearing loss and joint pain.