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Omodysplasia is a rare skeletal dysplasia characterized by severe limb shortening and facial dysmorphism. Two types of omodysplasia have been described: an autosomal recessive or generalized form (also referred to as micromelic dysplasia with dislocation of radius) marked by severe micromelic dwarfism with predominantly rhizomelic shortening of both the upper and lower limbs, and an autosomal dominant form in which stature is normal and shortening is limited to the upper limbs.
ORPHA:2733Classification level: Disorder
In total, less than 40 cases of omodysplasia have been described in the literature so far, with the majority of reported cases concerning the autosomal recessive form of the disease.
The facial dysmorphism is characterized by frontal bossing, a depressed nasal bridge with a short nose and a long and prominent philtrum. Decreased mobility of the elbows and knees is also a common feature. Other less frequent manifestations include midline hemangiomas, congenital heart defects, craniosynostosis and cryptorchidism in males.
The etiology remains unknown but a paternally-inherited paracentric inversion of 15q13 to q21.3 has been detected in one family.
Diagnosis is based on the clinical and radiological phenotype with major radiological findings including shortening and club-like tapering of the humeri and femora, proximal radioulnar diastasis and proximal radial head dislocation. Although the hands are generally considered to be normal in omodysplasia, short first metacarpals have been reported in the majority of patients with the autosomal dominant form.
The differential diagnosis for the autosomal recessive form should include diastrophic dysplasia, atelosteogenesis and Larsen syndrome (see these terms), whereas the major differential diagnosis for the autosomal dominant form is Robinow syndrome (see this term).
For affected families, detection of long bone anomalies by ultrasonography may allow prenatal diagnosis as early as at 13 weeks of gestation.
Genetic counseling should be recommended.
Management and treatment
Treatment is symptomatic only, involving mainly orthopedic management for recurrent joint dislocation.
The prognosis is variable.