P.4.8 X-linked benign form of myotubular myopathy (XLMTM) with necklace fibres: A case report

Abstract

X-linked myotubular myopathy (XLMTM) is usually a severe condition caused by mutations in myotubularin gen MTM1, (Xq28), a lipid inositide phosphatase acting in remodeling of membranes. Most of the affected patients present a severe neonatal form with hypotonia, weakness, facial diplegia, difficulties in sucking in addition to other symptoms dying within the first months. The biopsy features are consistent with the presence of central nuclei in most fibres. However, a more benign phenotype with a distinctive hallmark has recently been described. Herein, we present a four year old boy affected by this benign form. Patient was born by urgent caesarean section due to foetal bradycardia. He weighted 3.030 g. Presented axial hypotonic, scarce movements and respiratory distress, needing CPAP for few days. No tube feeding was required. Motor development was delayed. He had always difficulties in getting up from the floor. At 4 years he showed, facial weakness, weak cry, axial and head flexor muscles weakess. Cough was ineffective but no hypercapnia was detected. CK was normal. EMG was myopathic. Muscle biopsy showed two population of fibres. Most of the smaller one, revealed a “necklace” appearance. Genetic studies confirmed c.605T > C in exon 8 leading to p.I202S mutation in MTM1 gene. Necklace fibres constitute a hallmark for suspect diagnosis of this benign phenotype of XLMTM associated with mutation in the MTM1 gene. X-linked myotubular myopathy (XLMTM) is usually a severe condition caused by mutations in myotubularin gen MTM1, (Xq28), a lipid inositide phosphatase acting in remodeling of membranes. Most of the affected patients present a severe neonatal form with hypotonia, weakness, facial diplegia, difficulties in sucking in addition to other symptoms dying within the first months. The biopsy features are consistent with the presence of central nuclei in most fibres. However, a more benign phenotype with a distinctive hallmark has recently been described. Herein, we present a four year old boy affected by this benign form. Patient was born by urgent caesarean section due to foetal bradycardia. He weighted 3.030 g. Presented axial hypotonic, scarce movements and respiratory distress, needing CPAP for few days. No tube feeding was required. Motor development was delayed. He had always difficulties in getting up from the floor. At 4 years he showed, facial weakness, weak cry, axial and head flexor muscles weakess. Cough was ineffective but no hypercapnia was detected. CK was normal. EMG was myopathic. Muscle biopsy showed two population of fibres. Most of the smaller one, revealed a “necklace” appearance. Genetic studies confirmed c.605T > C in exon 8 leading to p.I202S mutation in MTM1 gene. Necklace fibres constitute a hallmark for suspect diagnosis of this benign phenotype of XLMTM associated with mutation in the MTM1 gene.