Résumé :
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X-linked myotubular myopathy is a rare disease, characterised by neonatal hypotonia, muscle weakness and respiratory distress in affected males, leading often to early death. It is caused by mutations in the MTM1gene, localised on the long arm of the X chromosome (Xq28), which encodes a phosphatase called myotubularin. To date, around 200 different mutations have been reported in the MTM1 gene, and most of them are private mutations. We report a novel MTM1 gene mutation in a neonate with X-linked myotubular myopathy. The boy was the first child of healthy non-consanguineous parents. There was no family history of neurological diseases. Pregnancy was characterized by reduction of fetal movements in the last months. At birth, he presented generalized muscle hypotonia, lack of spontaneous movements, respiratory insufficiency and he was intubated. Muscle biopsy revealed the typical features of myotubular myopathy. Molecular analysis of MTM1 gene revealed a novel MTM1 mutation in exon 14 (c.1481-1482delG, p.R494RfsX7). This mutation is predicted to result in the truncation of myotubularin, introducing a stop codon due to a frame shift, and were not detected in 100 healthy chromosomes. The mother did not carry the mutation supporting a de novo origin of this mutation. He was placed on ventilator since two months of age, and underwent a percutaneous endoscopic gastrostomy (PEG) at age of 5 months. He is currently 10 months-old with good respiratory monitor, progressive improvement of his nutritional indices and no complications to date. Since germline mosaicism has been described in several cases, prenatal diagnosis has been proposed to the family.
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