OBJECTIVES: To investigate whether (a) variants within the dopamine D2 receptor gene (DRD2) are associated with obesity and type 2 diabetes in Pima Indians, and (b) whether variation in this gene could be responsible for previously observed linkage to these phenotypes, at chromosome location 11q23 ± 24, in this population. DESIGN: Two single nucleotide polymorphisms (SNPs), Ser311Cys and TaqIA, within the DRD2 gene were genotyped by allelic discrimination PCR in subjects who had provided evidence of linkage to diabetes and obesity in an autosome-wide scan. SUBJECTS: A total of 1187 subjects were genotyped, including 947 full heritage Pima Indians (80%). Descriptive statistics for all subjects analyzed, for whom clinical data were available, were (mean AE s.d.): age at time of last exam 41 AE 15 y; birth year 1950 AE 14; age-sex-adjusted body mass index (BMI; adjusted to a mean age of 35 y) 36 AE 8 kgam 2 ; male 44%; diabetic 57%. For full heritage Pimas only: age 43 AE 15 y; birth year 1948 AE 14; sex ± age-adjusted BMI 36 AE 8 kgam 2 ; male 43%; diabetic 59%. RESULTS: Neither polymorphism was signi®cantly associated with diabetes in full heritage Pimas. Individuals with à CG' genotype at the Ser311Cys SNP had a higher BMI than those with a`CC' genotype (36.7 vs 35.5 kgam 2 , P 0.04). Linkage analysis of BMI, adjusted for either polymorphism, resulted in LOD scores that were similar to those obtained without adjustment. CONCLUSION: Heterozygotes at the Ser311Cys DRD2 polymorphism had a slightly higher BMI than homozygotes, however neither the Ser311Cys nor the TaqIA polymorphism accounted for the linkage with BMI on chromosome 11 in Pima Indians.

OBJECTIVE: To investigate whether the neuropeptide Y receptor 5 gene (NPY5R) is associated with obesity in humans. DESIGN: The NPY5R gene was screened for polymorphisms by direct sequencing in two groups of Pima Indians, selected for extremes of body mass index (BMI). Genotype frequencies were analyzed for association with BMI extreme. SUBJECTS: Full-heritage Pima Indians, non-diabetic and not ®rst degree relatives. Obese group: 19 Ma24 F, BMI 49 AE 7 kgam 2 (mean AE s.d.) age 24 AE 2 y, lean group: 16 Ma16 F, BMI 23 AE 2 kgam 2 , age 27 AE 3 y. MEASUREMENTS: Initially, the entire gene (proximal promoter, exon 1A, coding sequence, 5 H and 3 H UTRs) was sequenced in a subset of 20 individuals. No variants were found in the coding sequence, however three novel single nucleotide polymorphisms were detected in the non-coding regions: (1) a C?T transition located within the promoter 28 bp upstream of the exon 1A transcription start site; (2) a T?C transition 94 bp downstream of the stop codon; and (3) a G?A transition 432 bp downstream of the stop codon. The polymorphisms were then screened in all 75 subjects. RESULTS: The polymorphisms had mean heterozygosities of 0.34 ± 0.50 and were in strong linkage disequilibrium (P`0.001). Genotype frequencies differed signi®cantly in lean and obese Pimas for P2 (P 0.04) and for a triple haplotype (P 0.02, Bonferroni corrected). CONCLUSION: Considering the importance of this gene in regulation of body weight, the association of these polymorphisms with extremes of BMI in Pima Indians indicates that NPY5R, or a locus nearby, may contribute to susceptibility to obesity in this population.

Prior results from our genomic scan in Pima Indians indicated an obesity locus in a region on chromosome 11q23‐24 that was also linked to diabetes. Bivariate linkage analysis for the combined phenotype “diabesity” gave the strongest evidence for linkage (LOD = 5.2). Our aim is to positionally clone the gene(s) responsible for the linkage. Linkage disequilibrium mapping is being used to narrow the chromosomal region. Single nucleotide polymorphisms (SNPs) are being systematically identified and genotyped at 50‐kb intervals across the region of linkage. To date, 455 SNPs have been genotyped in 1229 Pimas. A region containing a cluster of SNPs strongly associated with BMI and a second region, approximately 2 Mb telomeric, containing a cluster of SNPs associated with diabetes have been preliminarily identified.