MTHFR is a key enzyme in folate metabolism. Some genetic polymorphisms code for a less efficient enzyme, increasing serum concentrations of homocysteine. This has been associated with inadequate feto-maternal circulation and increased risk of spontaneous abortion. Paroxonase 1 (PON1) is a multifunctional enzyme that can detoxify homocysteine through its homocysteine thiolactonase activity. We evaluate the association between MTHFR 677 C>T polymorphisms and non-recurrent spontaneous abortion and its interaction with PON1 polymorphisms involved in homocysteine metabolism in women living in floricultural areas in Mexico. Sociodemographic, reproductive history, folic acid consumption during pregnancy and environmental exposure data of 264 women who had been pregnant sometime during the 10 years prior to study enrolment were collected. MTHFR 677 C>T, PON1 192Q>R and PON1 55L>M genotypes were determined by PCR amplification. Information on pregnancy outcome and maternal genotypes was obtained for 484 pregnancies: 34 non-recurrent spontaneous abortions (gestational age < 20 weeks) and 450 controls. GEE models were used to evaluate the association between MTHFR polymorphism and non-recurrent spontaneous abortion, and its interaction with PON1 polymorphisms.
After adjusting for potential confounders, no significant association was found between the MTHFR 677 C>T maternal polymorphism and non-recurrent spontaneous abortion (OR CT vs CC= 0.39, 95% CI: 0.14-1.05; OR TT vs CC = 0.63, 95% CI: 1.22–1.80). No interactions with PON1 192Q>R or PON1 55L>M polymorphisms were identified (p for interaction = 0.88 and 0.41, respectively). PON1 55L>M maternal polymorphism was associated with higher risk of spontaneous abortion (OR LM/MM vs LL = 4.14, 95% CI: 1.49–11.54).
Our results do not demonstrate an interaction between the MTHFR 677 C>T and PON1 192Q>R or PON1 55L>M maternal polymorphisms neither an independent association of MTHFR 677 C>T polymorphism with non-recurrent spontaneous abortion, whereas PON1 55LM/MM maternal genotype increase the odds of this event.