Brain demyelination due to methionine adenosyltransferase deficiency OMIM:250850 MAT deficiency ICD10:E72.1 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. orphanet Methionine adenosyltransferase deficiency MAT I/III deficiency Rare genetic neurological disorder Disorder of methionine cycle and sulfur amino acid metabolism