The NM_001100.4(ACTA1):c.685A>G (p.Met229Val) variant in ACTA1 is a missense variant predicted to cause a substitution of methionine by valine at amino acid 229 (p.Met229Val). This variant is absent from gnomAD v4.1.0 (PM2_Supporting). ACTA1, in which the variant was identified, is defined by the ClinGen Congenital Myopathies VCEP as a gene that has a low rate of benign missense variation and where pathogenic missense variants are a common mechanism of dominant disease (PP2). The computational predictor REVEL gives a score of 0.854, which is above the threshold of 0.7, evidence that correlates with impact to ACTA1 function (PP3). Six different missense variants, [c.685A>T (p.Met229Leu), c.686T>G (p.Met229Arg), c.686T>C (p.Met229Thr), c.687G>A (p.Met229Ile), c.687G>C (p.Met229Ile), c.687G>T (p.Met229Ile)], in the same codon have been reported in patients with congenital myopathies (PMIDs: 12921789, 19562689, VCEP internal contributor], of which at least one has met the criteria to be classified as pathogenic by the ClinGen Congenital Myopathies VCEP (PM5). This variant has been observed in the heterozygous state in 4 individuals including a de novo occurrence in twins with clinical and histological features compatible with ACTA1-related myopathy including presence of numerous nemaline bodies (PS2, PS4_Moderate, PP4; PMIDs: 19562689, 15236405, 12921789). In summary, this variant meets the criteria to be classified as pathogenic for autosomal dominant alpha-actinopathy based on the ACMG/AMP criteria applied, as specified by the ClinGen Congenital Myopathies VCEP: PS2, PS4_Moderate, PM5, PM2_Supporting, PP2, PP3, PP4 (ClinGen Congenital Myopathies VCEP specifications version 2.0.0).