Myopathy in a woman and her daughter associated with a novel splice site MTM1 mutation.

• We have investigated a woman and her daughter with an early onset, slowly progressive myopathy. Muscle biopsy showed in both cases severe atrophy with marked fatty replacement. Frequent fibers with internalized nuclei were present but no typical features of centronuclear myopathy. There were also many fibers with deep invaginations of the plasma membrane. The presence of necklace fibers provided clue to correct genetic diagnosis. Both patients had a novel heterozygous splice site mutation in the myotubularin gene, MTM1 (c.867+1G>T). Analysis of MTM1 cDNA revealed that the mutation resulted in aberrant splicing with variable exon skipping. The expression of normal transcripts was markedly reduced and there was reduced expression of myotubularin protein. Although the expression of the allele without the mutation was reduced we did not obtain evidence of skewed X-chromosome inactivation. Other factors than skewed X-inactivation may cause allele inactivation and manifestation of severe myopathy in heterozygous carriers of pathogenic MTM1 mutations.

Subject headings

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine (hsv//eng)

Keyword

Aged

Exons

genetics

Family Health

Female

Genetic Association Studies

Humans

Microscopy

Electron

Transmission

Middle Aged

Mothers

Muscle

Skeletal

pathology

ultrastructure

Muscular Diseases

genetics

pathology

Mutation

genetics

Nuclear Family

Protein Tyrosine Phosphatases

Non-Receptor

genetics

metabolism

RNA Splicing

genetics

Publication and Content Type

ref (subject category)

art (subject category)