title: Polymorphisms in MTHFR, MS and CBS genes and homocysteine levels in a Pakistani population.
abstract: BACKGROUND
  Hyperhomocysteinemia (>15 µmol/L) is highly prevalent in South Asian populations including Pakistan. In order to investigate the genetic determinants of this condition, we studied 6 polymorphisms in genes of 3 enzymes--methylenetetrahydrofolate reductase (MTHFR; C677T; A1298C), methionine synthase (MS; A2756G), cystathionine-β-synthase (CBS; T833C/844ins68, G919A) involved in homocysteine metabolism and investigated their interactions with nutritional and environmental factors in a Pakistani population.
  
  
  RESULTS
  In a cross-sectional survey, 872 healthy adults (355 males and 517 females; age 18-60 years) were recruited from a low-income urban population in Karachi. Fasting venous blood was obtained and assessed for plasma/serum homocysteine; folate, vitamin B12, pyridoxal phosphate and blood lead. DNA was isolated and genotyping was performed by PCR-RFLP (restriction-fragment-length-polymorphism) based assays. The average changes in homocysteine levels for MTHFR 677CT and TT genotypes were positive [β(SE β), 2.01(0.63) and 16.19(1.8) µmol/L, respectively]. Contrary to MTHFR C677T polymorphism, the average changes in plasma homocysteine levels for MS 2756AG and GG variants were negative [β(SE β), -0.56(0.58) and -0.83(0.99) µmol/L, respectively]. The average change occurring for CBS 844ins68 heterozygous genotype (ancestral/insertion) was -1.88(0.81) µmol/L. The combined effect of MTHFR C677T, MS A2756G and CBS 844ins68 genotypes for plasma homocysteine levels was additive (p value <0.001). Odds of having hyperhomocysteinemia with MTHFR 677TT genotype was 10-fold compared to MTHFR 677CC genotype [OR (95%CI); 10.17(3.6-28.67)]. Protective effect towards hyperhomocysteinemia was observed with heterozygous (ancestral/insertion) genotype of CBS 844ins68 compared to homozygous ancestral type [OR (95% CI); 0.58 (0.34-0.99)]. Individuals with MTHFR 677CT or TT genotypes were at a greater risk of hyperhomocysteinemia in folate and vitamin B12 deficiencies and high blood lead (p value <0.05) level.
  
  
  CONCLUSIONS
  Gene polymorphism (especially MTHFR C677T transition), folate and vitamin B12 deficiencies, male gender and high blood lead level appear to be contributing towards the development of hyperhomocysteinemia in a Pakistani population.
authors.affiliation: Department of Biological and Biomedical Sciences, Aga Khan University, Karachi, Pakistan.
authors.forename: Mohsin
authors.initials: M
authors.lastname: Yakub
authors.forename: Naushad
authors.initials: N
authors.lastname: Moti
authors.forename: Siddiqa
authors.initials: S
authors.lastname: Parveen
authors.forename: Bushra
authors.initials: B
authors.lastname: Chaudhry
authors.forename: Iqbal
authors.initials: I
authors.lastname: Azam
authors.forename: Mohammad Perwaiz
authors.initials: MP
authors.lastname: Iqbal
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D003541:Cystathionine beta-Synthase / Q000235:genetics*; D005260:Female; D005492:Folic Acid / Q000097:blood; D005838:Genotype; D006579:Heterozygote; D006710:Homocysteine / Q000097:blood*; D006720:Homozygote; D006801:Humans; D020138:Hyperhomocysteinemia / Q000235:genetics; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics*; D008875:Middle Aged; D016017:Odds Ratio; D010154:Pakistan; D020641:Polymorphism, Single Nucleotide; D011732:Pyridoxal Phosphate / Q000097:blood; D012307:Risk Factors; D012737:Sex Factors; D014805:Vitamin B 12 / Q000097:blood; D055815:Young Adult
chemical_list: D006710:Homocysteine; D011732:Pyridoxal Phosphate; D005492:Folic Acid; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D003541:Cystathionine beta-Synthase; D014805:Vitamin B 12