Association of renal function and δ-aminolevulinic acid dehydratase polymorphism among Vietnamese and Singapore workers exposed to inorganic lead

Objectives: To investigate the effect of delta-aminolevulinic acid dehydratase (ALAD) polymorphisms on the association between blood lead and renal function among Vietnamese and Singaporean workers who were exposed to low to medium levels of inorganic lead, and to study the distribution of ALAD polymorphism among Vietnamese, Chinese, Malays and Indians. Methods: A total of 459 male and female workers were studied. Blood and urine were collected for each worker in order to determine ALAD genotype, blood lead, and urinary d-aminolevulinic acid (ALAU). Renal function tests included urine albumin (Ualb), urine beta 2 microglobulin (U beta 2m), urinary alpha 1 microglobulin (U alpha 1m), N-acetyl-glucosaminidas (NAG), and urine retinol blinding protein (RBP). A multiple regression model with interaction term was applied to fit the entire data and to explore the modifying effect of ALAD polymorphism on the relation of blood lead to each renal function parameter. Results: ALAD1-1 was the predominant genotype for all the ethnic groups while ALAD2-2 was the rarest. The frequency of ALAD2 allele was higher among Malays (8.8%) and Indians (10.6%) compared to the Chinese (5.0%) and Vietnamese (4.3%). The geometric mean of blood lead for all workers was 19.0 mu g/dl. The models for Ub2m, Ua1m, and NAG showed that the ALAD1-2/2-2 group had higher beta coefficients than the ALAD1-1 group. Corresponding to 10 mg/dl blood lead, ALAD1-1 homozygotes had an increment of 1.288 mu g/ g Cr, 1.175 mg/ g Cr, and 1.995 U/g Cr for U beta 2m, U alpha 1m, and NAG, respectively. ALAD1- 2/2-2 subjects had higher increments of 3.802 mu g/ g Cr, 2.138 mg/g Cr, and 3.89 U/g Cr for U beta 2m, U alpha 1m, and NAG, respectively. Conclusion: The frequency of the ALAD2 allele is as low in Vietnamese workers as in Chinese. Workers with the ALAD2 allele appeared more susceptible to the effects of lead ( especially at higher levels) on renal function.