Ethnic variation in genotype frequencies of delta-aminolevulinic acid dehydratase (ALAD)

Delta-aminolevulinic acid dehydratase (ALAD) is a cytosolic enzyme in the heme biosynthetic pathway. The ALAD is controlled by two codominant alleles (ALAD1 and ALAD2), which result in a Asn-Lys substitution at amino acid position 59 of the mature enzyme based on a single nucleotide polymorphism (SNP) (G177C) leading three phenotypes (ALAD1-1, ALAD1-2, and ALAD2-2). Previous studies have shown that this polymorphism is related to lead toxicity. There is little evidence showing interethnic differences in the distribution of this polymorphism. We examined the distribution of genetic variants of the ALAD G177C polymorphism in four Asians, three Africans, and three Mexicans. Genomic DNA was extracted from blood or bloodstain, and the genotypes for the ALAD polymorphism were determined by PCR followed by RFLP digestion and gel electrophoresis. We found a notable interethnic disparity in the distribution of ALAD G177C genotypes and alleles. The frequencies of ALAD2 in Asian populations were comparable to those in Caucasians, while Africans had no mutation allele. These findings may help us understand the interethnic disparities in susceptibility to lead toxicity.