Delta-Aminolevulinic Acid Dehydratase Genotype and Its Relationship with Blood Lead and Zinc Protoporphyrin Levels in Lead-Exposed Children Living in a Smelter Community in Northern Mexico

摘要

The implications of delta-aminolevulinic acid dehydratase (ALAD) polymorphism for lead kinetics and toxicity have been mainly studied in occupationally exposed adults. Therefore, our purpose was to evaluate the distribution of ALAD genotype and its association with biomarkers of exposure (PbB levels) and effect (Blood ZPP) among children living in a smelter community in Mexico. We recruited 569 children from nine elementary schools close to a smelter site. PbB was determined by electrothermal atomic absorption spectrometry. A polymerase chain reaction (PCR)-based protocol was used for ALAD genotyping. Zinc protoporphyrin (ZPP) in blood was measured by direct fluorometry. Most children (93.15%) were homozygous for ALAD1"1, 6.67% were heterozygous for ALAD for1 2, and one child was homozygous for ALAD22. There was an increased proportion of ALAD12/2"2 genotype with respect to PbB levels. The ZPP geometric mean was slightly higher in ALAD1"1 genotype children (63.48 /Ltmol ZPP/mol Hb) than in those having the ALAD-2 genotype (58.22 ^tmol ZPP/mol Hb; p = 0.051). Linear and quadratic models showed significant relationships between ZPP and PbB. A significant increase in the odds ratio (OR) for the effect of lead exposure on ZPP levels was observed for ALAD11 children having PbB values above 20 fig/dh, as compared to those having PbB levels below 10 mug/dL (OR = 2.95, 95% CI = 1.45-5.97; p = 0.003), whereas no significant increases were observed for the ALAD1"2/2"2 children. In summary, our results suggest that heme biosynthesis was less affected in ALAD12/2"2 lead-exposed children than in those carrying the ALAD1"1 genotype.