Comparison of a hypervariable segment in the human dopamine D4 receptor (DRD4) gene between the Japanese and Mongolian populations.

Amplifiable length polymorphism (AmpFLP) genotyping and direct sequencing of a hypervariable segment in the human dopamine D4 receptor (DRD4) gene were performed from genomic DNA of 100 unrelated Japanese and Mongolian individuals. The 4-repeat allele (314 bp) was the most prevalent and appeared at 0.88 and 0.82 in the Japanese and Mongolian populations, respectively. Homogeneity test of distribution showed no significant deviation from the observed frequencies of genotypes between the Japanese and Mongolian populations, but sequence analysis of the 4-repeat allele indicated that there could be ethnic differences between the two populations at the nucleotide level. The DRD4 allele and genotype frequencies in 10 patients with Parkinson's disease did not differ from those in the control Japanese population. In one Parkinsonian patient, however, a nucleotide change in one of the 4-repeat alleles was discovered. These results suggest that there could be ethnic and/or individual differences in the specific nucleotide changes within the repeat sequence because some alleles with the same number of repeat units had sequence variations. Thus, the DRD4 polymorphism exists at two levels and therefore could be a useful marker for forensic identification and anthropological studies.