A case of congenital fiber-type disproportion syndrome presenting dilated cardiomyopathy with ACTA1 mutation

Abstract

Background: Actin, alpha, skeletal muscle 1 (ACTA1) is one of the causative genes of nemaline myopathy (NM) and congenital fiber-type disproportion (CFTD). CFTD is characterized by type 1 fiber atrophy and distinguished from NM in the absence of rods. Eight patients with CFTD, including one patient with dilated cardiomyopathy (DCM), have previously been reported. Herein, we report the case of a 10-year-old boy presenting with CFTD and DCM.

Methods: We performed exome sequencing and analyzed the effect of Met327Lys mutations on cultured C2C12 muscle cells compared with that seen in the wild type (WT, ACTA1) and previously identified Asp294Val mutations associated with a severe phenotype of CFTD without cardiomyopathy.

Results: Exome sequencing revealed a de novo mutation, c.980 T > A, p.(Met327Lys), in ACTA1 (NM_001100.4). C2C12 cells transfected with the WT plasmid expressed ACTA1 in the nucleus and cytoplasm. Cells with the Asp294Val mutant showed needle-like structures in the cytoplasm, whereas the expression of the Met327Lys mutant resulted in few aggregations but many apoptotic cells.

Conclusion: Apoptosis induced in Met327Lys-transfected muscle cells supports the pathogenicity of the mutation and can be implicated as one of the histopathological features associated with CFTD, as in NM.

Keywords: actin; alpha; apoptosis; congenital fiber-type disproportion; dilated cardiomyopathy; skeletal muscle 1.

FIGURE 1

WT and mutant ACTA1 proteins were expressed in C2C12 cells. The nucleus is stained by Fluoro‐KEEPER Antifade Reagent Nonhardening Type with DAPI (Nacalai Tesque), and F‐actin is stained by ActinRed™555 (Invitrogen). pAcGFP‐N1 plasmids with ACTA1‐WT, ACTA1‐Asp294Val, and ACTA1‐Met327Lys are transfected into C2C12 cells. The yellow bar indicates 20 μm. WT ACTA1 is expressed in the nucleus and cytoplasm with few aggregations (a, b). Asp294Val mutation (previously reported), positive control, shows needle‐like structures in the cytoplasm (c, d). Met327Lys mutation, as found in our case here, shows few aggregations in the cytoplasm and numerous apoptotic cells (e–h). White arrows indicate apoptotic cells (e, g), and the arrowhead indicates aggregations (e).

FIGURE 2

Clinical features of cardiomyopathy with ACTA1 mutations (a), schematic representation of the ACTA1 gene (b), and three‐dimensional (3D) model of the ACTA1 monomer (c). (b)The hinge domains are at 137–150 amino acids (AA) and 333–338 AA. Two actin‐binding sites are at 112–125 AA and 360–372 AA. Sites of actin‐binding to cytosolic chaperonin containing TCP‐1 (CCT) are at 30–34 AA, 135–139 AA, 170–174 AA, 240–254 AA, 265–274 AA, and 340–349 AA. (b, c) Arrows indicate the mutations in Figure 2a. The mutations written in red are associated with congenital fiber‐type disproportion (CFTD). Asterisk indicates our patient. The ACTA1 monomer has been illustrated by AlphaFold Protein Structure Database (https://alphafold.ebi.ac.uk/).