A dual diagnosis was obtained in a child with clinically diagnosed atypical Down syndrome (P41), which included long myopathic facies, scapular winging, tapered calves, infantile spasms, severe muscle weakness, and hypotonia, who was found to harbor both trisomy 21 and a maternally inherited, likely pathogenic ACTA1 SNV associated with nemaline myopathy. The gene discussed is ACTA1; the disease is Down syndrome.