rs1801394, also known as A66G or Ile22Met, is a SNP in the methionine synthase MTRR gene. This gene encodes one of the two enzymes involved in the production of methionine (the other is MTR). The protein encoded by an rs1801394 allele has a lower affinity for MTR ([PMID 12416982]) and is inconsistently associated with homocysteine level, although it is a risk factor for neural tube defects ([PMID 10444342]) and Down syndrome ([PMID 10930360]) in conditions of higher homocysteine.
Based on a study of British patients with primary brain tumors, (1,005 glioma cases and 631 meningioma cases), rs1801394(G;G) individuals were at higher risk for meningioma (odds ratio 1.41, CI: 1.02-1.94). In general, genotypes associated with increased 5,10-methylenetetrahydrofolate levels are associated with elevated risk for these types of brain cancer.[PMID 18483342]
|Disease Association||Defects in MTRR are the cause of methylcobalamin deficiency type E (cblE) (MIM:236270); also known as vitamin B12- responsive homocystinuria or homocystinuria-megaloblastic anemia complementation type E. Patients who are defective in reductive activation of methionine synthase exhibit megaloblastic anemia, developmental delay, hypomethioninemia, and hyperhomocysteinemia, a risk factor in cardiovascular disease and neural tube defects. It is an autosomal recessive disease.|
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|Disease||Neural tube defects, Down syndrome|
|CLNDBN||Neural tube defects, folate-sensitive, susceptibility to, Down syndrome, susceptibility to|
|CLNSRC||OMIM Allelic Variant|
|qualified_impact||Low clinical importance, Likely pathogenic|
|summary||This common variant (HapMap allele frequency of 31.3%) in a protein involved in folate (B9) and cobalamin (B12) metabolism and is often reported as "MTRR I22M" (an alternative transcript position). Mothers homozygous for this variant are associated with having around a increased chance of a child with Down syndrome (risk of 0.4%, average risk in population is 0.25%). Notably, age plays a far larger role in the rate of Down syndrome (risk is 4.5% for a mother 45-years-of-age), and it is unknown how this variant may combine with the effect of age. There are conflicting reports associating this variant with incidence of neural tube defects, possibly when combined with MTHFR A222V.|
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