Nemaline myopathy is a rare disorder of varying severity and genetic etiology. We present two cases, a father and son, with a novel missense mutation in the alpha actin gene. Both have a history of early motor impairment, with the son's course being considerably more severe. This pair illustrates the clinical variability of nemaline myopathy, highlighting the possible influence of environmental and epigenetic factors. Implications for the current classification system and prognosis are discussed.