Monarch Disease Ontology id MONDO_0017051 (classic maple syrup urine disease) (classic MSUD) is the most severe and probably common form of MSUD characterized by a maple syrup odor in the cerumen at birth, poor feeding, lethargy and focal dystonia, followed by progressive encephalopathy and central respiratory failure if untreated. Also known as: classic BCKD deficiency, classic MSUD, classic branched-chain 2-ketoacid dehydrogenase deficiency, classic branched-chain alpha-ketoacid dehydrogenase deficiency, classic branched-chain ketoaciduria.