Environ Health Perspect

BackgroundLead poisoning affects many organs in the body. Lead inhibits \uce\ub4-aminolevulinic acid dehydratase (ALAD), an enzyme with two co-dominantly expressed alleles, ALAD1 and ALAD2.ObjectiveOur meta-analysis studied the effects of the ALAD polymorphism on a) blood and bone lead levels and b) indicators of target organ toxicity.Data sourceWe included studies reporting one or more of the following by individuals with genotypes ALAD1-1 and ALAD1-2/2-2: blood lead level (BLL), tibia or trabecular lead level, zinc protoporphyrin (ZPP), hemoglobin, serum creatinine, blood urea nitrogen (BUN), dimercaptosuccinic acid\ue2\u20ac\u201cchelatable lead, or blood pressure.Data extractionSample sizes, means, and standard deviations were extracted for the genotype groups.Data synthesisThere was a statistically significant association between ALAD2 carriers and higher BLL in lead-exposed workers (weighted mean differences of 1.93 \uce\ubcg/dL). There was no association with ALAD carrier status among environmentally exposed adults with BLLs < 10 \uce\ubcg/dL. ALAD2 carriers were potentially protected against adverse hemapoietic effects (ZPP and hemoglobin levels), perhaps because of decreased lead bioavailability to heme pathway enzymes.ConclusionCarriers of the ALAD2 allele had higher BLLs than those who were ALAD1 homozygous and higher hemoglobin and lower ZPP, and the latter seems to be inversely related to BLL. Effects on other organs were not well delineated, partly because of the small number of subjects studied and potential modifications caused by other proteins in target tissues or by other polymorphic genes