We describe an atypical case of nemaline myopathy with an unusual distribution of muscle weakness who presented at 14 years of age with kyphoscoliosis. In this patient, we demonstrate heterozygosity for a de novo CGT-CAT (Arg167His) mutation in a constitutively expressed exon (exon 5) of slow alpha-tropomyosin (TPM3). This is the first mutation identified in a constitutively expressed exon of TPM3 in a nemaline myopathy patient, but is similar to recently described mutations in beta-tropomyosin (TPM2) associated with nemaline myopathy and mutations in fast alpha-tropomyosin (TPM1) which cause hypertrophic cardiomyopathy.