A recurrent ACTA1 amino acid change in mosaic form causes milder asymmetric myopathy

Vilma Lotta Lehtokari, Lydia Sagath, Mark Davis, Desiree Ho, Kirsi Kiiski, Kaisa Kettunen, Matthew Demczko, Riki Stein, Matteo Vatta, Thomas L. Winder, Adi Shohet, Naama Orenstein, Peter Krcho, Peter Bohuš, Sanna Huovinen, Bjarne Udd, Katarina Pelin, Nigel G. Laing, Carina Wallgren-Pettersson

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We describe three patients with asymmetric congenital myopathy without definite nemaline bodies and one patient with severe nemaline myopathy. In all four patients, the phenotype had been caused by pathogenic missense variants in ACTA1 leading to the same amino acid change, p.(Gly247Arg). The three patients with milder myopathy were mosaic for their variants. In contrast, in the severely affected patient, the missense variant was present in a de novo, constitutional form. The grade of mosaicism in the three mosaic patients ranged between 20 % and 40 %. We speculate that the milder clinical and histological manifestations of the same ACTA1 variant in the patients with mosaicism reflect the lower abundance of mutant actin in their muscle tissue. Similarly, the asymmetry of body growth and muscle weakness may be a consequence of the affected cells being unevenly distributed. The partial improvement in muscle strength with age in patients with mosaicism might be due to an increased proportion over time of nuclei carrying and expressing two normal alleles.

Original languageEnglish
Pages (from-to)32-40
Number of pages9
Early online dateNov 2023
Publication statusPublished - Jan 2024
Publication typeA1 Journal article-refereed


  • ACTA1
  • Congenital myopathy
  • Genetic mosaicism
  • Nemaline myopathy
  • Skeletal muscle alpha-actin

Publication forum classification

  • Publication forum level 1

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Neurology
  • Clinical Neurology
  • Genetics(clinical)


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