hypermethioninemia with deficiency of S-adenosylhomocysteine hydrolase (MONDO_0013404, a Monarch Disease Ontology term) can be described as follows. Psychomotor retardation due to S-adenosylhomocysteine hydrolase deficiency is characterized by psychomotor delay and severe myopathy (hypotonia, absent tendon reflexes and delayed myelination) from birth, associated with hypermethioninaemia and elevated serum creatine kinase levels. Also known as: hypermethioninemia due to S-adenosylhomocysteine hydrolase deficiency, psychomotor retardation due to S-adenosylhomocysteine hydrolase deficiency.