ASSOCIATIONS OF DELTA-AMINOLEVULINIC-ACID DEHYDRATASE GENOTYPE WITH PLANT, EXPOSURE DURATION, AND BLOOD LEAD AND ZINC PROTOPORPHYRIN LEVELSIN KOREAN LEAD WORKERS

Previous studies have suggested that polymorphisms in delta-aminolevul inic acid dehydratase (ALAD), a heme synthetic enzyme, may be associat ed with differences in blood lead levels, perhaps due to differential binding of lead in erythrocytes. The authors examined associations of ALAD genotype with blood lead and zinc protoporphyrin (ZPP) levels, ex posure duration, sex, and plant in 308 currently exposed lead workers in three lead storage battery manufacturing plants in the Republic of Korea in 1993. The overall prevalence of the variant allele, ALAD(2), was 11%, but prevalence varied by plant (p = 0.02: 8.6% in plant A, 20 % in plant B, and 22% in plant C). While ALAD(2) was not associated wi th mean blood lead levels, the allele was associated with blood lead l evels greater than or equal to 40 mu g/dl (crude odds ratio (OR) = 2.6 , 95% confidence interval (Cl) 1.1-6.3; adjusted OR = 2.3, 95% Cl 0.8- 6.2, with adjustment for sex, plant, and exposure duration) and with e xposure durations greater than 6 years (adjusted OR = 2.5, 95% Cl 1.2- 5.4, with adjustment for blood lead, sex, and plant). Among workers in plant C, the highest exposure plant, ALAD(2) was associated with lowe r ZPP levels when controlling for blood lead levels. These data sugges t that lead toxicokinetics may be modified by ALAD genotype and that A LAD(2) may be protective for the health effects of lead. ALAD genotype also appears to have been a selection factor for current lead exposur e status in the studied workers.