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What is Methylenetetrahydrofolate reductase deficiency and explain in detail?
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.Common variants of MTHFR deficiency are asymptomatic and have only minor effects on disease risk. Severe variants (from nonsense mutations) are vanishingly rare.

Symptoms
The common MTHFR deficiencies are usually asymptomatic, although the 677T variant can cause a mildly increased risk of some diseases.
For individuals homozygous in the 677T variant, there is a mildly elevated risk of thromboembolism (odds ratio 1.2), and stroke (odds ratio 1.26). There is also an elevated risk of neural tube defects among children of individuals with the C677T polymorphism (odds ratio 1.38).For cardiovascular risk, common MTHFR deficiencies were once thought to be associated but meta-analyses indicate that correlation this was an artifact of publication bias.

Causes
MTHFR is the rate-limiting enzyme in the methyl cycle, which includes the conversion of homocysteine into methionine. Defects in variants of MTHFR can therefore lead to hyperhomocysteinemia.There are two common variants of MTHFR deficiency. In the more significant of the two, the individual is homozygous for the 677T polymorphism. This variant in particular is the most common genetic cause of hyperhomocysteinemia. The resulting enzyme is thermolabile and in homozygotes, enzymatic activity is depressed to 35% of its usual level. The second variant is a milder one, caused by a homologous 1298C polymorphism