Previously, we reported a genome-wide scan for nicotine dependence (ND) in the African American (AA) sample of the Mid-South Tobacco Family (MSTF) cohort. In this study, we conducted a genome-wide scan in 629 individuals representing 200 nuclear families of European American (EA) origin of the MSTF cohort with the goals of identifying vulnerability loci for ND in the EAs and determining converging regions across the ethnic groups. We examined 385 autosomal microsatellite markers for ND, which was assessed by smoking quantity (SQ), the Heaviness of Smoking Index (HSI) and the Fagerströ m test for ND (FTND). After performing linkage analyses using various methods implemented in the GENEHUNTER and SAGE programs, we found eight regions on chromosomes 2, 4, 9-12, 17 and 18 that met the criteria for suggestive linkage to at least one ND measure in the EA sample. Of these, the region on chromosome 4 at 43 cM showed suggestive linkage to indexed SQ, the HSI and the FTND, and the region on chromosome 9 at 24 cM showed suggestive linkage to the HSI and the FTND. To increase detection power, we analyzed a combined AA and EA sample using age, gender and ethnicity as covariates and found that the region on chromosome 12 near marker D12S372 showed significant linkage to SQ. Additionally, we found six regions on chromosomes 9-11, 13 and 18 that showed suggestive linkage to at least one ND measure in the combined sample. When we compared the linkage peaks detected for ND among the two samples and a combined sample, we found that four regions on chromosomes 9 (two regions), 11 and 18 overlapped. On the other hand, we identified five regions on chromosomes 2, 4, 10, 12 and 17 that showed linkage to ND only in the EA sample, and two regions on chromosomes 10 and 13 that showed linkage to ND only in the AA sample. For those linkages identified in only one sample, we found that the combined analysis of AA plus EA samples actually decreased the linkage signal. This indicates that some chromosomal regions may be more homogenous than others across the ethnic samples. All regions except for the one on chromosome 12 have been detected at nominally significant levels in other studies, providing independent replication of ND loci in different populations.

Our previous linkage study demonstrated that the 9q22-q23 chromosome region showed a 'suggestive' linkage to nicotine dependence (ND) in the Framingham Heart Study population. In this study, we provide further evidence for the linkage of this region to ND in an independent sample. Within this region, the gene encoding Src homology 2 domain-containing transforming protein C3 (SHC3) represents a plausible candidate for association with ND, assessed by smoking quantity (SQ), the Heaviness of Smoking Index (HSI) and the Fagerströ m Test for ND (FTND). We utilized 11 single-nucleotide polymorphisms within SHC3 to examine the association with ND in 602 nuclear families of either African-American (AA) or EuropeanAmerican (EA) origin. Individual SNP-based analysis indicated three SNPs for AAs and one for EAs were significantly associated with at least one ND measure. Haplotype analysis revealed that the haplotypes A-C-T-A-T-A of rs12519-rs3750399-rs4877042-rs2297313-rs1547696-rs1331188, with a frequency of 27.8 and 17.6%, and C-T-A-G-T of rs3750399-rs4877042-rs2297313-rs3818668-rs1547696, at a frequency of 44.7 and 30.6% in the AA and Combined samples, respectively, were significantly inversely associated with the ND measures. In the EA sample, another haplotype with a frequency of 10.6%, A-G-T-G of rs1331188-rs1556384-rs4534195-rs1411836, showed a significant inverse association with ND measures. These associations remained significant after Bonferroni correction. We further demonstrated the SHC3 contributed 40.1-59.2% (depending on the ND measures) of the linkage signals detected on chromosome 9. As further support, we found that nicotine administered through infusion increased the Shc3 mRNA level by 60% in the rat striatum, and decreased it by 22% in the nucleus accumbens (NA). At the protein level, Shc3 was decreased by 38.0% in the NA and showed no change in the striatum. Together, these findings strongly implicate SHC3 in the etiology of ND, which represents an important biological candidate for further investigation.

Cigarette smoking is the leading preventable cause of death in the US. Although smoking behavior has a significant genetic determination, the specific genes and associated mechanisms underlying smoking behavior are largely unknown. Here, we performed a genome-wide association study on smoking behavior in 840 Caucasians, including 417 males and 423 females, in which we examined ∼380,000 SNPs. We found that a cluster of nine SNPs upstream from the IL15 gene were associated with smoking status in males, with the most significant SNP, rs4956302, achieving a p value (8.80×10−8) of genome-wide significance. Another SNP, rs17354547, that is highly conserved across multiple species, achieved a p value of 5.65×10−5. These two SNPs, together with two additional SNPs (rs1402812 and rs4956396) were selected from the above nine SNPs for replication in an African-American sample containing 1,251 subjects, including 412 males and 839 females. The SNP rs17354547 was successfully replicated in the male subgroup of the replication sample; it was associated with smoking quantity (SQ), the Heaviness of Smoking Index (HSI) and the Fagerstrom Test for Nicotine Dependence (FTND), with p values of 0.031, 0.0046 and 0.019, respectively. In addition, a haplotype formed by rs17354547, rs1402812 and rs4956396 was also associated with SQ, HSI and FTND, achieving p values of 0.039, 0.0093 and 0.0093, respectively. To further confirm our findings, we performed an in silico replication study of the nine SNPs in a Framingham Heart Study sample containing 7,623 Caucasians from 1,731 families, among which, 3,491 subjects are males and 4,132 are females. Again, male-specific association with smoking status was observed, for which seven of the nine SNPs achieved significant p values (p<0.05) and two achieved marginally significant p values (p<0.10) in males. Several of the nine SNPs, including the highly conserved one across species, rs17354547, are located at potential transcription factor binding sites, suggesting transcription regulation as a possible function for these SNPs. Through this function, the SNPs may modulate gene expression of IL15, a key cytokine regulating immune function. As the immune system has long been recognized to influence drug addiction behavior, our association findings suggest a novel mechanism for smoking addiction involving immune modulation via the IL15 pathway.

A pathway-focused complementary DNA microarray and gene ontology analysis were used to investigate gene expression profiles in the amygdala, hippocampus, nucleus accumbens, prefrontal cortex (PFC) and ventral tegmental area of C3H/HeJ and C57BL/6J mice receiving nicotine in drinking water (100 μg/ml in 2% saccharin for 2 weeks). A balanced experimental design and rigorous statistical analysis have led to the identification of 3.5-22.1% and 4.1-14.3% of the 638 sequence-verified genes as significantly modulated in the aforementioned brain regions of the C3H/HeJ and C57BL/6J strains, respectively. Comparisons of differential expression among brain tissues showed that only a small number of genes were altered in multiple brain regions, suggesting presence of a brain region-specific transcriptional response to nicotine. Subsequent principal component analysis and Expression Analysis Systematic Explorer analysis showed significant enrichment of biological processes both in C3H/HeJ and C57BL/6J mice, i.e. cell cycle/proliferation, organogenesis and transmission of nerve impulse. Finally, we verified the observed changes in expression using real-time reverse transcriptase polymerase chain reaction for six representative genes in the PFC region, providing an independent replication of our microarray results. Together, this report represents the first comprehensive gene expression profiling investigation of the changes caused by nicotine in brain tissues of the two mouse strains known to exhibit differential behavioral and physiological responses to nicotine. © 2007 Blackwell Publishing Ltd

In the US, African Americans and other minority groups have longer wait times to deceased donor kidney transplantation than Caucasians. To date, the role of geographic distribution of racial and ethnic groups as a determinant of wait times has not been fully elucidated. Using the Scientific Registry of Transplant Recipients database, all registrants for kidney transplant between 2004 and 2007 (n = 126 094) were analyzed from time of waitlisting until nonzero antigen mismatched deceased donor kidney transplant. Nationally, deceased donor transplantation occurred at a lower rate for African Americans (hazard ratio [HR] 0.85, confidence interval [CI] 0.83–0.87), Hispanics (HR 0.68, CI 0.66–0.70), Asians/Pacific Islanders (HR 0.77, CI 0.73–0.80) and Other minority groups (HR 0.74, CI 0.69–0.81) compared to Caucasians. Multivariate modeling for age, gender, cause of end-stage renal disease, ABO type, panel reactive antibody, HLA-DR frequency, expanded criteria donor status and prior kidney donation only partially accounted for this difference. Adjusting for these variables and organ procurement organization of listing, African Americans (HR 1.03, CI 1.00–1.06), Hispanics (HR 1.15, CI 1.10–1.19), Asians/Pacific Islanders (HR 1.36, CI 1.30–1.43) and Other minority groups (HR 1.00, CI 0.92–1.09) were transplanted at similar or higher rates than Caucasians. Our findings show that geographic location of waitlisted candidates is the most important contributor to racial disparities in waiting times for deceased donor kidney transplantation.