What causes nemaline myopathy 5 (NEM5)?

Updated: Mar 11, 2019
  • Author: Matthew Harmelink, MD; Chief Editor: Amy Kao, MD  more...
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Answer

NEM5 is due to an autosomal recessive mutation in the gene for troponin T1 (TNNT1) and has been described only in the Old Order Amish. [20]  The mutation causes a premature stop codon. The truncated protein removes the principal site of binding to troponin C and troponin I. It is hypothesized that the mutation results in mutant message undergoing nonsense-mediated decay or an unstable protein that is degraded. There is therfore a complete loss of troponin T1. Early compensation at birth may be due to fetal transcription of TNNT2 and TNNT3. [21]

Onset is during  the first few months of life with hypotonia, proximal weakness as well as jaw and limb tremors that resolve over a few months. Death occurs before age 2 years from respiratory failure. Other features include shoulder and hip contractures and pectus carinatum.


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