A rare disorder leading to a deficiency of complex I of the respiratory chain and is characterized by neurological dysfunction, hepatic failure and cardiomyopathy. The disease is acyl-CoA dehydrogenase 9 deficiency (MONDO_0012624, a Monarch Disease Ontology identifier). Also known as: ACAD9 deficiency, mitochondrial complex I deficiency due to ACAD9 deficiency, mitochondrial complex I deficiency, nuclear type 20.