Effects of ALAD genotype on the relationship between lead exposure and anthropometry in a Cohort of Mexican children

Abstract

ObjectivesLead exposure is associated with children's growth, but this relationship may depend on the presence of susceptibility factors, including genetic variation. Blood lead levels (BLL) differ by ALAD (aminolevulinic acid dehydratase) genotype. We investigated the association between BLL and growth in Mexican first-graders with different ALAD genotypes. MethodsChildren between the ages of 6–8 years (n = 602) attending first grade in schools within the vicinity of a metal foundry in Torreón, Mexico were enrolled into a randomized controlled trial (RCT) testing the efficacy of iron and/or zinc supplementation on blood lead levels (BLL) and cognition. BLL and anthropometry were assessed at baseline (height, height-for-age z-score (HAZ), knee height, head circumference), after 6 (head circumference) and 12 months (height, HAZ, knee height). Children with ALAD1–1 and ALAD1–2/2–2 were compared. The study sample included 538 and 470 participants who had complete data at baseline and follow-up, respectively. Separate multivariable linear regression models adjusted for covariates were used to test the association between BLL at baseline and each anthropometric measure. Covariates included age, sex, hemoglobin, crowding, and maternal education. BLL x ALAD genotype interaction term was tested. ResultsMedian BLL (10.1 μg/dL) did not differ by ALAD genotype. After covariate adjustment, baseline BLL was inversely associated with baseline height, HAZ, and knee height. The association (β [95% CI]) between BLL and baseline height (−0.38[−0.68, −0.09]), HAZ (−0.07[−0.12, −0.02]) and knee height (−0.14[−0.25, −0.02]), was somewhat stronger in children with ALAD1–2/2–2 than ALAD1–1 (−0.09[−0.16, −0.02], −0.02[−0.03, −0.004] and −0.04[−0.06, −0.01], respectively). No associations between BLL and growth at 6 or 12 months were detected irrespective of ALAD genotype. ConclusionsBLL was adversely associated with anthropometric measures among Mexican children. ALAD genotype may be a susceptibility factor for the effects of lead on child growth.