Choline metabolic pathway gene polymorphisms and risk for Down syndrome: An association study in a population with folate-homocysteine metabolic impairment.

BACKGROUND/OBJECTIVES: Choline is an essential nutrient involved in one-carbon metabolism, but its role in mechanisms underlying meiotic non-disjunction is poorly known. The relationship between folate-homocysteine metabolic pathway gene polymorphism and Down syndrome (DS) risk has been widely analyzed, but there are limited reports on its correlation with choline metabolism. In the present case-control association study, we investigated the relationship of three single-nucleotide polymorphisms (SNPs) (phosphatidylethanolamine N-methyltransferase (PEMT) rs12325817, choline dehydrogenase (CHDH) rs12676 and homocysteine methyltransferase (BHMT) rs3733890) of choline metabolism with risk for DS. SUBJECT/METHODS: Genotyping of 228 mothers of a down syndrome child (DSM) and 200 control mothers (CMs) for all SNPs was performed by PCR coupled with restriction fragment length polymorphism method. RESULTS: A significantly increased risk for BHMT +742AA genotype with an odds ratio of 4.96 (95% confidence interval (CI): 1.66-14.88, P=0.0036) was observed. For PEMT rs12325817 and CHDH rs12676, no significant difference in allelic and genotypic frequencies was observed. In genotypic combination analysis considering PEMT -744GG/CHDH +432GG/BHMT +742GG as the reference combination, PEMT -744GC/CHDH +432GG/BHMT +742GG genotypic combination was significantly higher in DSM compared with that in CMs with an odds ratio of 2.061 (95% CI: 1.10-3.86, P=0.0342). We also observed an epistatic interaction between methylenetetrahydrofolate reductase (MTHFR) rs1801133 and choline metabolic pathway gene variants. CONCLUSIONS: Our findings indicate impaired choline metabolism showing a greater risk for DS, especially in a population associated with homocysteine-folate impairment. Further studies are required to confirm our findings.

Role of folate-homocysteine pathway gene polymorphisms and nutritional cofactors in Down syndrome: A triad study.

STUDY QUESTION: Do gene-gene and gene-environment interactions in folate-homocysteine (Hcy) pathway have a predisposing role for Down syndrome (DS)? SUMMARY ANSWER: The study provides evidence that in addition to advanced age, maternal genotype, micronutrient deficiency and elevated Hcy levels, individually and in combination, are risk factors for Down syndrome. WHAT IS KNOWN ALREADY: Polymorphisms in certain folate-Hcy-pathway genes (especially the T allele of MTHFR C677T), elevated Hcy and poor folate levels in mothers during pregnancy have been shown to be risk factors for Down syndrome in certain Asian populations (including the eastern region of India), while the same SNPs are not a risk factor in European populations. This conflicting situation alludes to differential gene-environment (nutrition) interactions in different populations which needs to be explored. STUDY DESIGN, SIZE, DURATION: Between 2008 and 2012, 151 Down syndrome triads and 200 age-matched controls (Control mothers n = 186) were included in the study. Seven polymorphisms in six genes of folate-Hcy metabolic pathway, along with Hcy, cysteine (Cys), vitamin B12 (vit-B12) and folate levels, were analysed and compared among the case and control groups. PARTICIPANTS/MATERIALS, SETTING, METHODS: Genotyping was performed by the PCR-RFLP technique. Levels of homocysteine and cysteine were measured by HPLC while vitamin B12 and folate were estimated by chemiluminescence. MAIN RESULTS AND THE ROLE OF CHANCE: We demonstrate that polymorphisms in the folate-Hcy pathway genes in mothers collectively constitute a genotypic risk for DS which is effectively modified by interactions among genes and by the environment affecting folate, Hcy and vitamin B12 levels. The study also supports the idea that these maternal risk factors provide an adaptive advantage during pregnancy supporting live birth of the DS child. LIMITATIONS AND REASONS FOR CAUTION: Our inability to obtain genotype and nutritional assessments of unaffected siblings of the DS children was an important limitation of the study. Also, its confinement to a specific geographic region (the eastern part) of India, and relatively small sample size is a limitation. A parallel investigation on another population could add greater authenticity to the data. WIDER IMPLICATIONS OF THE FINDINGS: For mothers genetically susceptible to deliver a DS child (particularly in South Asia), peri-conceptional nutritional supplementation and antenatal care could potentially reduce the risk of a DS child. Additionally, nutritional strategies could possibly be used for better management of the symptoms of DS children. STUDY FUNDING/COMPETING INTERESTS: The work is funded through Programme support for Genetic disorders by Department of Biotechnology, Government of India to R.R. The authors declare no conflict of interest.

Association of MTHFR and RFC1 gene polymorphism with hyperhomocysteinemia and its modulation by vitamin B12 and folic acid in an Indian population.

BACKGROUND/OBJECTIVES: Unlike most Western populations, MTHFR 677T is a rare allele and a risk factor for a variety of disorders in India. What kind of nutritional (environmental) and/or genetic factors could contribute to the genetic risk is not known. To assess the incidence of hyperhomocysteinemia and its correlation with the polymorphism in homocysteine (Hcy)-pathway genes and associated cofactors in the native populations of eastern India. SUBJECTS/METHODS: Healthy population from four eastern states of India. Genotyping of SNPs, HPLC and chemiluminescence-based assay for homocysteine, vitamin B12 and folic acid. RESULTS: Approximately 30% of the population has hyperhomocysteinemia (>15 µmol/lit; hypHcy) with varying frequencies in the four states from where samples were collected (n=1426). Polymorphisms of MTR and CBS do not affect hypHcy. 677T and 1298C alleles of MTHFR and G80 RFC-1 show association with hypHcy. In contrast, RFC-1 80AA is protective even in presence of 677T MTHFR. Addition of each mutant allele has an additive effect on Hcy level. Vitamin B12 (cofactor in methionine synthesis) clearly modulates the genotypic effect on Hcy level. Although frequency of individuals with low folic acid is ≈11, 49% of the population is vitamin B12 deficient (<220 pg/lit) and has a significant negative correlation with Hcy. Individuals with optimum vitamin B12 and folic acid generally have low Hcy, even in risk genotypes. CONCLUSIONS: One of the plausible reasons for susceptibility of individuals with MTHFR C677T in the studied population to various disorders is the high frequency of hyperhomocysteinemia and vitamin B12 deficiency in the 'healthy population'. Apparently, supplementation of vitamin B(12) to this health-impoverished community may help lessen the risk of several multifactorial disorders.