A de novo dominant mutation in ACTA1 causing congenital nemaline myopathy associated with a milder phenotype: expanding the spectrum of dominant ACTA1 mutations.

We describe the presentation and six-year follow up of a child with nemaline myopathy due to a de novo mutation in the skeletal muscle α-actin gene (ACTA1) characterized by dramatic improvement during the early childhood years. The presentation in this female patient was infantile-onset weakness in the facial, bulbar, respiratory and neck flexor muscles. A six-year follow-up revealed continued progressive improvement in her muscle strength. Based upon the histopathologic and ultrastructural features of nemaline rod disease, ACTA1 was sequenced. This revealed a mutation in exon 4 of ACTA1 (c.557A>G). Our report further expands the phenotypic spectrum associated with ACTA1 mutations. Although it is difficult to infer any genotype-phenotype correlation, this report stimulates the discussion regarding the pathophysiologic mechanism of the clinical improvement seen in some patients with ACTA1 mutations.