ABSTRACT
Hypermetioninemia is a group of rare diseases defined by plasma methionine elevation. The causes of hypermethioninemia include genetic and non-genetic factors. Affecting the transmethylation process in the metabolic pathway between methionine and homocysteine is the common inherited methylation disorders. Most patients had completely asymptomatic and only biochemical abnormalities,others with clinical symptoms were also non-specific, such as mental retardation, cognitive impairment, moderate hepatomegaly, dystonia, Marfans syndrome type,osteoporosis,and cardiovascular disease,and etc. A low methionine diet treatment is rec-ommended,the importance of neonatal screening is emphasized and the birth defects can be reduced through pre-natal diagnosis,but the necessity remains controversial. The long-term prognosis of this disorders is unknown,the plasma of methionine should be measured at regular intervals,and the individualized follow-up is very important.