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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.
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. [9] There are two common variants of MTHFR deficiency. In the more significant of the two, the individual is homozygous for the 677T polymorphism.
Co-expression of this mutation and the 677T polymorphism in methionine tetrahydrofolate reductase (MTHFR) Methylenetetrahydrofolate reductase act to further the extent of DNA damage. [36] Hypomethylation due to impaired methylation up regulates atherosclerotic susceptible genes whilst down regulating atherosclerosis protective genes. [36]
Mutations in this gene can lead to reduced methylation at CpG sites, and these changes in methylation patterns may increase susceptibility for type 2 diabetes. The most common at the gene encoding MTHFR is the C677t mutation. This is not a spontaneous mutation; it is actually hereditary.
A functional single-nucleotide polymorphism (a common normal variant) of the gene for catechol-O-methyltransferase results in a valine to methionine mutation at position 158 (Val 158 Met) rs4680. [15] In vitro, the homozygous Val variant metabolizes dopamine at up to four times the rate of its methionine counterpart. [22]
There are two different forms of the estrogen receptor, usually referred to as α and β, each encoded by a separate gene (ESR1 and ESR2, respectively).Hormone-activated estrogen receptors form dimers, and, since the two forms are coexpressed in many cell types, the receptors may form ERα (αα) or ERβ (ββ) homodimers or ERαβ (αβ) heterodimers. [3]
They are named because of sequence homology with estrogen receptors, but do not appear to bind estrogens or other tested steroid hormones. There are three human estrogen related receptors: ERRα ; ERRβ ; ERRγ ; ERRs bind enhancers throughout the genome where they exert effects on gene regulation.
Mutations in ERβ have been shown to influence cardiomyocytes, the cells that comprise the largest part of the heart, and can lead to an increased risk of cardiovascular disease (CVD). There is a disparity in prevalence of CVD between pre- and post-menopausal women, and the difference can be attributed to estrogen levels.