Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 109

The SMN1 gene and, to a lesser extent, the SMN2 gene are responsible for the production of survival motor neuron proteins, which inhibit degradation of anterior horn cells and motor nuclei. Most cases of spinal muscular atrophy are caused by a deletion or mutation in SMN1, found on chromosome 5, resulting in deficient protein production. In a noncarrier, there is typically one copy of SMN1 per chromosome, although rarely two copies can be present on the same chromosome. The number of copies of SMN2 per chromosome ranges from zero to three. In affected individuals, SMN2 copy number modifies the overall production of the protein, with a greater copy number corresponding to milder clinical phenotypes (types 3 and 4).