Hypermethioninemia with S-adenosylhomocysteine hydrolase deficiency is an autosomal recessive severe neurometabolic disorder affecting the muscles, liver, and nervous system, resulting in death in infancy (summary by Bas et al., 2020). Other causes of hypermethioninemia include hereditary tyrosinemia (276700), cystathionine beta-synthase deficiency (236200), and methionine adenosyltransferase deficiency (250850).