Revisão sistemática e metanálise da associação entre polimorfismos genéticos maternos envolvidos no metabolismo do folato e o nascimento de indivíduos com Síndrome de Down

Abstract

Introduction Down syndrome (DS) is caused by the presence of three copies of chromosome 21 in consequence to chromosome nondisjunction in maternal meiosis observed in about 95% of cases. Genetic polymorphisms involved in folate metabolism were associated with the maternal risk for DS. However, the results are contradictories. Objectives To perform a systematic review and meta-analysis in order to evaluate the association between Methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, Methionine synthase reductase (MTRR) A66G, Methionine synthase (MTR) A2756G, Reduced folate carrier 1 (RFC1) A80G, Cystathionine β-synthase (CβS) 844ins68, Methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) G1958A and Transcobalamin 2 (TC2) C776G genetic polymorphisms and the maternal risk for DS. Methods Studies were searched up to May 2014 on MEDLINE, EMBASE, LILACS, hand searched reference lists of published articles and conference meetings and personal communication. Case-control studies that evaluated the association between genetic polymorphisms in case mothers (DSM) and controls mothers (CM) were included. DSM are considered mothers that have gave birth to children with free trisomy of 21 chromosome and CM are considered mothers that have gave birth to children without chromosomal abnormality, syndrome or malformation. Studies with mothers of DS individuals with translocation or mosaicism, case reports, editorials and review articles were excluded. Data extraction and quality assessment were performed independently by two investigators. Meta-analysis assesses the associations between each genetic polymorphism and maternal risk for DS by dominant, recessive, codominant and allelic genetic models. Dichotomous outcome measures were pooled using fixed and random effects models and the results were expressed by odds ratio (OR) with 95% confidence intervals (95% CI). Heterogeneity between studies was evaluated using Q test and the I2 and subgroup and sensitivity analyses were performed in order to investigate the potential sources of heterogeneity. Publication bias was estimated using funnel plot and linear regression test. Results Collectively, 30 case-control studies including 3,101 DSM and 3,967 CM were included. Significant association between MTHFR C677T and MTRR A66G polymorphisms and maternal risk for DS was found when all population is considered. Subgroup and sensitivity analyses according ethnicity showed significant associations for the MTHFR C677T polymorphism in Caucasians, Brazilians and Asians and for the MTRR A66G polymorphism in Caucasians. Additionally, the results of the RFC1 A80G polymorphism demonstrated significant association, it was also found in Asians and maternal age less than 35 years at conception subgroups analyses. Finally, MTHFD1 1958GA genotype was revealed as maternal risk factor for DS when only studies with control group in Hardy-Weinberg equilibrium were considered. No association among MTHFR A1298C, MTR A2756G, CβS 844ins68 and TC2 C776G polymorphisms and maternal risk for DS was found. Conclusions MTHFR C677T, MTRR A66G, RFC1 A80G and MTHFD1 1958GA polymorphisms are associated with maternal risk for DS.