D2 dopamine receptor gene polymorphisms among African-Americans and Mexican-Americans: a lung cancer case-control study.

Recent research suggests that variant alleles (A1 and B1) of the DRD2 gene play a role in determining smoking status. However, no studies have evaluated these variant alleles in African-Americans and Mexican-Americans. The primary objective of this study, therefore, was to test the hypothesis that ever smokers in these ethnic groups are more likely than never smokers to have the DRD2 alleles associated with tobacco use (A1 and B1). Furthermore, because of a predicted higher prevalence of smokers in a family because of the patterns of inheritance of the genotypes associated with tobacco use, we also anticipated that individuals with these at-risk DRD2 alleles would be more likely to have a family history of smoking-related cancers. Because other inherited genetic variants may interact with smoking on cancer risk, we also hypothesized that this association might differ between cancer patients and control subjects. PCR was used to perform genotyping on peripheral WBC DNA from 140 lung cancer patients (43 Mexican-Americans and 97 African-Americans) and 222 age-, sex-, and ethnicity-matched controls (111 Mexican-Americans and 111 African-Americans). A personal family history was obtained from each participant. There were no statistically significant differences in the distribution of the DRD2 genotypes between cases and controls, although the frequency of the B1 genotype significantly differed by ethnicity (P = 0.002 for controls and P = 0.001 for cases). The DRD2 genotypes and smoking status showed a correlation among Mexican-American controls, although not among African-American controls. The cigarette pack-years in control subjects for the two ethnic groups combined were 30.8, 21.9, and 18.6 for the A1A1, A1A2, and A2A2 genotypes and 36.5, 20.8, and 18.5 for the B1B1, B1B2, and B2B2 genotypes, respectively. Similar trends were found for the number of cigarettes smoked per day among control subjects. From the standpoint of polymorphisms, however, there was a borderline significantly increased (3.6 times greater) frequency of smoking-related cancers among the first-degree relatives of case subjects with an A1 allele than among those without an A1 allele. There was also an elevated (1.8 times greater) frequency of smoking-related cancer among first-degree relatives of case subjects with a B1 allele compared with patients without a B1 allele, but this finding was not statistically significant. This phenomenon was not observed among control subjects. We noted a trend toward interaction of DRD2 A1 genotypes and case status for increased risk of smoking-related cancer among first-degree relatives. These findings suggest that the variant DRD2 genotypes are associated with a greater likelihood to smoke and a greater smoking intensity, as well as with a familial aggregation of smoking-related cancers. However, a large study is needed to confirm this finding.