Mitochondrial DNA depletion, encephalomyopathic form, with methylmalonic aciduria is associated with mutations in SUCLA2, the gene encoding a beta subunit of succinate-CoA ligase, where 17 patients have been reported. Mutations in SUCLG1, encoding the alpha subunit of the enzyme, have been reported in only one family, where a homozygous 2 bp deletion was associated with fatal infantile lactic acidosis. We here report a patient with a novel homozygous missense mutation in SUCLG1, whose phenotype is similar to that of patients with SUCLA2 mutations.