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Distal hereditary motor neuropathy, type V is a progressive disorder that affects nerve cells in the spinal cord and weakens muscles in the hands and feet.
Symptoms of distal hereditary motor neuropathy, type V usually begin during adolescence, but onset varies from infancy to the mid-thirties. Cramps in the hand induced by the cold are often the initial symptom. The main characteristics of this disorder are weakness and wasting away (atrophy) of hand muscles, specifically on the thumb side of the index finger and in the palm at the base of the thumb. Foot abnormalities, such as a high arch (pes cavus), are also common. People with this disorder lead active lives and have normal life expectancies.
The incidence of distal hereditary motor neuropathy, type V is unknown; only a small number of cases have been reported.
Mutations in the BSCL2 and GARS genes cause distal hereditary motor neuropathy, type V.
The BSCL2 gene provides instructions for making a protein called seipin, whose function is unknown. Mutations in the BSCL2 gene likely alter the shape and structure of seipin. It is unclear how the altered seipin protein impairs nerves that control muscles in the hands and feet.
The GARS gene provides instructions for making an enzyme that is involved in the production (synthesis) of proteins. It remains unclear how GARS mutations lead to distal hereditary motor neuropathy, type V. GARS mutations may disrupt protein synthesis in nerve cells, which impairs the function of the nerve fiber (axon) that transmits nerve impulses. As a result, nerve cells slowly lose the ability to communicate with muscles in the hands and feet.
This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.