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Methylenetetrahydrofolate reductase deficiency is the most common genetic cause of elevated serum levels of homocysteine (hyperhomocysteinemia). It is caused by genetic defects in MTHFR, which is an important enzyme in the methyl cycle. [1] Common variants of MTHFR deficiency are asymptomatic and have only minor effects on disease risk. [2]
Methylenetetrahydrofolate reductase (MTHFR) is the rate-limiting enzyme in the methyl cycle, and it is encoded by the MTHFR gene. [5] Methylenetetrahydrofolate reductase catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate , a cosubstrate for homocysteine remethylation to methionine .
Vitamin B 12 deficiency prevents the 5-methyltetrahydrofolate (5-MTHF) form of folate from being converted into THF due to the "methyl trap". [18] This disrupts the folate pathway and leads to an increase in homocysteine which damages cells (for example, damage to endothelial cells can result in increased risk of thrombosis).
5,10-Methenyltetrahydrofolate (5,10-CH=THF) is a form of tetrahydrofolate that is an intermediate in metabolism. 5,10-CH=THF is a coenzyme that accepts and donates methenyl (CH=) groups. It is produced from 5,10-methylenetetrahydrofolate by either a NAD+ dependent methylenetetrahydrofolate dehydrogenase , or a NADP+ dependent dehydrogenase . [ 1 ]
5,10-Methenyltetrahydrofolate synthetase deficiency (MTHFS deficiency) is a rare neurodevelopmental disorder caused by mutations affecting the MTHFS gene, which encodes the enzyme 5,10-Methenyltetrahydrofolate synthetase. [2] The disease starts at birth or in early infancy and presents with microcephaly, short stature, and developmental delay.
5,10-Methylenetetrahydrofolate (N5,N10-Methylenetetrahydrofolate; 5,10-CH 2-THF) is cofactor in several biochemical reactions. It exists in nature as the diastereoisomer [6R]-5,10-methylene-THF. As an intermediate in one-carbon metabolism, 5,10-CH 2 -THF converts to 5-methyltetrahydrofolate , 5-formyltetrahydrofolate , and methenyltetrahydrofolate.
The systematic name of this enzyme class is 5,10-methylenetetrahydrofolate,FADH2:dUMP C-methyltransferase. Other names in common use include Thy1 , and ThyX . This enzyme participates in pyrimidine metabolism and one carbon pool by folate .
This methionine can then be converted back to SAM, completing the cycle. [5] In the rate-limiting step of the SAM cycle, MTHFR (methylenetetrahydrofolate reductase) irreversibly reduces 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. [6]