The delta-aminolevulinate dehydratase polymorphism: higher blood lead levels in lead workers and environmentally exposed children with the 1-2 and 2-2 isozymes.

The erythrocyte delta-aminolevulinate dehydratase (ALAD) isozyme phenotypes and the blood lead levels were determined in a population of 202 lead factory workers in Germany and an environmentally exposed population of 1278 children in New York who had elevated free protoporphyrin levels. In both population, individuals with the ALAD 1-2 or 2-2 isozyme phenotype had levels of blood lead statistically higher than those individuals with the ALAD 1-1 isozyme phenotype (lead workers: P greater than 0.004; children: P greater than 0.0001). Homozygotes and heterozygotes for the ALAD2 allele who expressed the 2-2 or 1-2 isozyme phenotype had median blood lead levels that were about 9 to 11 micrograms/dl greater than similarly exposed individuals who were homozygous for the ALAD1 allele. These findings support the hypothesis that the ALAD2 polypeptide binds lead more effectively, and therefore that individuals with the ALAD2 allele may be more susceptible to lead poisoning.