Characterization of mutations in the myotubularin gene in twenty six patients with X-linked myotubular myopathy |
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Authors: | de Gouyon BM; Zhao W; Laporte J; Mandel JL; Metzenberg A; Herman GE |
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Institution: | Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA. |
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Abstract: | A candidate gene, myotubularin, involved in the pathogenesis of X- linked
myotubular myopathy (MTM1) was isolated recently. Mutations originally were
identified in 12% of patients examined for 40% of the coding sequence,
raising the possibility that additional genes could be responsible for a
proportion of X-linked cases. We report here the identification of
mutations in 26 of 41 independent male patients with muscle biopsy-proven
MTM, by direct genomic sequencing of 92% of the known coding sequence of
the myotubularin gene. Eighteen patients had point mutations, including one
A/G transition found in four patients which alters a splice acceptor site
in exon 12 and leads to a three amino acid insertion. Six patients had
small deletions involving <6 bp, while two larger deletions encompassed
two or six exons, respectively. No differences were noted among the types
of mutations between familial and sporadic cases. However, all of the five
patients with a mild phenotype had missense mutations. While 50% of the
mutations were found in exons 4 and 12, and three distinct mutations were
found in more than one patient, no single mutation accounted for more than
10% of the cases. The low frequency of large deletions and the varied
mutations identified suggest that direct mutation screening for molecular
diagnosis may require gene sequencing.
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