Newborn MTHFR rs1801133 Variant and Extremely Low Birth Weight: A Case-Control Study and Meta-Analysis.

Background: Extremely low birth weight (ELBW) and extremely low gestational age (ELGA) remain major challenges in neonatology, contributing to neonatal morbidity and mortality. This study aims to examine the association between functional variants of MTHFR and PON1, genes involved in homocysteine metabolism, and the risk of ELGA, ELBW, and other complications of prematurity. A meta-analysis was also conducted to integrate literature data with the results of this study. Methods: The study included 377 premature infants, 164 mothers, and a population-based sample of 404 individuals. Genotyping was performed using TaqMan assays. Results: The fetal, but not maternal, MTHFR rs1801133 genotype was associated with ELBW (OR = 1.65; 95% CI: 1.09-2.51; p = 0.017, dominant model), bronchopulmonary dysplasia (p = 0.028), patent ductus arteriosus (p = 0.017), and neonatal mortality. The meta-analysis, which included five studies spanning 1156 cases and 1124 controls, confirmed the association between the neonatal MTHFR genotype and low birth weight (LBW), demonstrating an association of the rs1801133T allele with LBW in the TT homozygote model (vs. CT: OR = 1.41; 95% CI: 1.08-1.80; p = 0.0097). Subgroup analyses indicated that the rs1801133T allele is a protective factor against LBW in more developed countries, such as Canada and the UK (dominant model), whereas in other countries, such as China, Turkey, and Poland, it is a risk factor for LBW (recessive model). No association with PON1 variants with ELBW or ELGA was found. Conclusions: This study provides the first global evidence confirming that the neonatal MTHFR genotype contributes to LBW, underscoring the population-specific effects of this genetic variant.