Two Cases of X-Linked Myotubular Myopathy with Novel MTM1 Mutations

BACKGROUND: Myotubular myopathy (MTM) is a congenital myopathy characterized by centrally placed nuclei in muscle fibers. Mutations in the myotubularin 1 gene (MTM1) have been identified in the most of the patients with the X-linked recessive form. CASE REPORT: This report describes two male infants with X-linked MTM (XLMTM). Both patients presented with generalized hypotonia and respiratory difficulties since birth. We did not perform a muscle biopsy in either patient, but their conditions were diagnosed by genetic testing of MTM1. One splicing mutation, c.63+1G>C, and a frame-shift mutation, c.473delA (p. Lys158SerfxX28), were identified. Neither mutation has been reported previously. CONCLUSIONS: Genetic testing for MTM1 is helpful for the differential diagnosis of floppy male infants. We suggest that advanced molecular genetic testing may permit a correct diagnosis while avoiding invasive procedures.

Mutation studies in x-linked myotubular myopathy in three indian families.

Congenital myopathies are a group of genetic disorders characterized by generalised muscle hypotonia and weakness of varying severity. They are distinct entities and do not include muscular dystrophies, metabolic myopathies and mitochondrial disorders. Myotubular myopathy is a rare sub type within this group of disorders. Clinical differentiation of the various types is difficult and requires muscle biopsy with histopathological and immunohistochemical studies for specific diagnosis. Gene studies are a prerequisite for genetic counseling adn prenatal diagnosis. Here presented three cases of X-linked myotubular myopathy in three Indian families where the diagnosis was established by mutation analysis in the MTM1 gene in all, and supported his histopathology in two. All three families had history of previous male neontal deaths with similar complaints. Molecular analysis revealed hemizygous mutations in the MTM1 gene including c.1261-10A>G in case, 1, c.70C>T (R24X) in case 2, and a previously unreported mutation, c.924_926delCTT(p. F308del), in case 3. Genetic counseling was performed regarding the X-linked inheritance, their 50% risk of recurrence in boys in subsequent pregnancies, and a feasibility of prenatal diagnosis. This is the first report of cases of X-linked Myotubular myopathy from India.

A Genome-Wide Screening in Saccharomyces cerevisiae for Suppressor Genes of MTM1 / 生物化学与生物物理进展

MTM1 gene is essential for SOD2 activity and normal mitochondrial function. MTM1 deletion results in decreased SOD2 activity, impaired mitochondrial function and growth defect on nonfermentable carbon source. A yeast genomic library was transformed into mtm1 deletion mutant to screen for suppressor genes of MTM1. The damage caused by MTM1 deletion is irreversible and even overexpression of MTM1 can not rescue the growth defect of mtm1 deletion mutant. Another screening strategy was adopted: a plasmid overexpressing MTM1 was transformed into wild type before the MTM1 gene on chromosome was deleted. The resulting strain, designated YES2MTM1, was transformed with a yeast genomic library. Transformants lost the plasmid overexpressing MTM1 after 5-FOA treatment. Yeast strains able to grow on nonfermentable carbon source with MTM1 deletion and overexpression of some DNA fragments were picked up and candidate suppressor genes were identified. Overexpression of five genes were identified to be able to rescue the growth defect on nonfermentable carbon source. The study will provide reference for MTM1 gene function and screening for suppressor of genes whose deletion result in irreversible damage.