Two Cases of X-Linked Myotubular Myopathy with Novel MTM1 Mutations
A 6-month-old male infant was transferred to our hospital due to failure to extubate. He was born at 38 weeks of gestation with a birth weight of 2590 g. His Apgar scores were 2 and 4 at 1 and 5 minutes, respectively. He was the third baby of non-consanguineous parents, and his two female siblings were reported to be healthy. No history of maternal disease or family history of neuromuscular diseases was reported by the parents. Reduced fetal movements or polyhydramnios were not noticed during pregnancy. At birth he was severely hypotonic with poor respiration, and required immediate ventilator support. He experienced 10 episodes of extubation failure up to 6 months of age. On admission to our hospital at the age of 6 months, the baby was extremely floppy with an absence of deep tendon reflexes. He had a characteristic myopathic face with paucity of facial expression. A high arched palate was also noted, but tongue fasciculation was not observed. His serum creatine kinase level was 31 IU/L. Brain magnetic resonance imaging revealed nonspecific findings, and so we suspected that the patient had peripheral hypotonia. Molecular genetic tests were performed for the diseases that can cause peripheral types of congenital hypotonia, including congenital type of muscular dystrophy type 1, spinal muscular atrophy, and Prader-Willi syndrome; all of the results were negative, whereas the study for MTM1 revealed a novel deletion mutation, c.473delA (p. Lys158SerfxX28) (), which is presumed to result in the premature truncated myotubularin protein. A muscle biopsy was refused by the parents. His mother is a carrier for this mutation. The patient is now 9 months old and is being maintained on a home ventilator.