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Otospondylomegaepiphyseal dysplasia (OSMED) is a genetic disorder of bone growth that results in skeletal abnormalities, severe hearing loss, and distinctive facial features. The name of the condition indicates that it involves the ears (oto-), affects the bones of the spine (spondylo-), and enlarges the ends (epiphyses) of long bones in the arms and legs. The features of OSMED are similar to those of another skeletal disorder, Weissenbacher-Zweymüller syndrome.
People with this condition are often shorter than average because the bones in their arms and legs are unusually short. Other skeletal features include enlarged joints, short hands and fingers, and flattened bones of the spine (platyspondyly). People with the disorder often experience back and joint pain, limited joint movement, and arthritis that begins early in life.
Severe high-tone hearing loss is common in people with OSMED. Typical facial features include protruding eyes; a sunken bridge of the nose; an upturned nose with a large, rounded tip; and a small lower jaw. Virtually all affected infants are born with an opening in the roof of the mouth (a cleft palate). The skeletal features of OSMED tend to diminish during childhood, and jaw growth catches up with age.
The frequency of this disorder is unknown, but it is very rare. Only a few families with the condition have been reported.
Mutations in the COL11A2 gene cause otospondylomegaepiphyseal dysplasia.
The COL11A2 gene is one of several genes that provide instructions for the production of type XI collagen. This type of collagen is important for the normal development of bones and other tissues that form the body's supportive framework (connective tissues). Mutations in the COL11A2 gene that cause OSMED disrupt the production or assembly of type XI collagen molecules. The loss of type XI collagen prevents bones and other connective tissues from developing properly.
OSMED is likely inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.