A mitochondrial complex III deficiency characterized by onset at birth of lactic acidosis, hypotonia, hypoglycemia, failure to thrive, encephalopathy, and delayed psychomotor development and that has_material_basis_in homozygous or compound heterozygous mutation in the nuclear-encoded BCS1L gene on chromosome 2q35. [ url:http://omim.org/entry/124000?search=124000&highlight=124000 http://purl.obolibrary.org/obo/ECO_0007636 ]