Hypermethioninemia with deficiency of S-adenosylhomocysteine hydrolase

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.