Myotubular myopathy , X - linked (X-linked myotubular myopathy) - Gen MTM1.
Myotubular X - linked myopathy is a disease that mainly affects skeletal muscles and affects almost exclusively in males. People with this disorder have myopathy and hypotonia, which are usually evident at birth. Muscle problems myotubular X - linked myopathy impair the development of motor skills such as sitting, standing and walking. Because muscle weakness, affected individuals may have difficulty with feeding, lack of muscle strength to breathe, ophthalmoplegia and areflexia. Often, muscle weakness disrupts the normal development of bones and can lead to brittle bones, scoliosis and deformities of the joints of the hips and knees.
Other signs and symptoms of the disease may include a large head with a long , narrow face, liver disease, respiratory infections and recurrent ear and seizures. Due to severe respiratory problems, those affected usually survive only in early childhood however, some people with this condition have lived to adulthood.
Myotubular myopathy , X - linked is caused by mutations in the gene MTM1, located on the long arm of chromosome X (Xq28). This gene encodes a myotubularin l enzyme. It is believed that this enzyme is involved in the development and maintenance of muscle cells. This enzyme acts as a phosphatase, removing phosphate groups from other molecules phosphatidylinositol phosphate and phosphatidylinositol 3 molecules -bifosfato 3.5. These molecules are found in cell membranes and is likely involved in transporting molecules into cells.
There are more than 200 mutations in the gene cause the disease MTM1. Some mutations change the amino acid myotubularin enzyme, while other mutations result in an abnormally short nonfunctional enzyme. These mutations alter the function of the enzyme in the maintenance and development of muscle cells, causing muscle weakness and other signs and symptoms of the disease.
This disease is inherited in a recessive X - linked pattern. The gene associated with the disease is on the X chromosome in males, an altered copy of the gene in each cell is sufficient to cause disease. In women, a mutation must be present in both copies of the gene to cause the disorder. Because it is unlikely that women have two altered copies of this gene, males are affected by recessive X - linked disorders much more frequently than women. A feature of the X - linked inheritance is that fathers can not pass X - linked traits to their sons chromosome. Myotubular in X - linked myopathy, the affected male inherits an altered copy of her mother in the 80 to 90 percent of cases. In the remaining 10 to 20 percent of cases, the disorder results from a new mutation in the gene that occurs during the formation of the reproductive cells of parental or early embryonic development. Women with an altered copy of the gene MTM1 generally have no signs and symptoms of the disease. However, in rare cases, women with an altered copy of the gene have some mild muscle weakness.
Tests performed in IVAMI: in IVAMI perform detection of mutations associated with X - linked myotubular myopathy, by complete PCR amplification of exons MTM1 gene, and subsequent sequencing.
Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).