Novel autosomal dominant TNNT1 mutation causing nemaline myopathy

Area of Science:

• Genetics
• Molecular Biology
• Neuromuscular Disorders

Background:

• Nemaline myopathy (NEM) is a congenital myopathy characterized by muscle weakness and nemaline rods.
• Mutations in the troponin T1 (TNNT1) gene are a known cause of NEM.
• Previously identified TNNT1 mutations were typically homozygous nonsense or compound heterozygous truncating/deletion mutations.

Observation:

• A large family exhibited autosomal dominant nemaline myopathy.
• Genetic analysis revealed a novel heterozygous missense mutation (c.311A>T, p.E104V) in the TNNT1 gene.
• Muscle biopsies showed nemaline rods and type 1 fiber hypotrophy.

Findings:

• The identified TNNT1 mutation segregated in an autosomal dominant pattern.
• This mutation affects a highly conserved residue.
• No other causative mutations were found in known NEM genes.

Implications:

• This study identifies a new mechanism for NEM inheritance: autosomal dominant.
• The novel TNNT1 mutation likely functions through a dominant-negative effect.
• This expands the spectrum of TNNT1 mutations associated with nemaline myopathy.