A single patient with hypertrophic cardiomyopathy carried a nonsense mutation in MTATP8 [130], whereas few patients with hypertrophic cardiomyopathy and heart failure [131] or ataxia and peripheral neuropathy [132] harbored a heteroplasmic mtDNA variant, resulting in concurrent substitutions in the overlapping MTATP6 and MTATP8 genes. The gene discussed is MT-ATP6; the disease is cerebellar ataxia.