Hypermethioninemia due to methionine adenosyltransferase deficiency is a very rare metabolic disorder resulting in isolated hepatic hypermethioninemia that is usually benign due to partial inactivation of enzyme activity. Rarely patients have been found to have an odd odor or neurological disorders such as brain demyelination. The disease is Monarch Disease Ontology id MONDO_0009607 (methionine adenosyltransferase deficiency). Also known as: MAT I/III deficiency, MAT deficiency, brain demyelination due to methionine adenosyltransferase deficiency, hypermethioninemia, persistent, autosomal dominant, due to methionine adenosyltransferase I/III deficiency, isolated persistent hypermethioninemia, methionine adenosyltransferase deficiency, autosomal recessive.