Nominal association with CHRNA4 variants and nicotine dependence.

Nicotine binds to nicotinic acetylcholine receptors and studies in animal models have shown that α4ß2 receptors mediate many behavioral effects of nicotine. Human genetics studies have provided support that variation in the gene that codes for the α4 subunit influences nicotine dependence (ND), but the evidence for the involvement of the ß2 subunit gene is less convincing. In this study, we examined the genetic association between variation in the genes that code for the α4 (CHRNA4) and ß2 (CHRNB2) subunits of the nicotinic acetylcholine receptor and a quantitative measure of lifetime DSM-IV ND symptom counts. We performed this analysis in two longitudinal family-based studies focused on adolescent antisocial drug abuse: the Center on Antisocial Drug Dependence (CADD, N = 313 families) and Genetics of Antisocial Drug Dependence (GADD, N = 111 families). Family-based association tests were used to examine associations between 14 single nucleotide polymorphisms (SNPs) in CHRNA4 and CHRNB2 and ND symptoms. Symptom counts were corrected for age, sex and clinical status prior to the association analysis. Results, when the samples were combined, provided modest evidence that SNPs in CHRNA4 are associated with ND. The minor allele at both rs1044394 (A; Z = 1.988, P = 0.047, unadjusted P-value) and rs1044396 (G; Z = 2.398, P = 0.017, unadjusted P-value) was associated with increased risk of ND symptoms. These data provide suggestive evidence that variation in the α4 subunit of the nicotinic acetylcholine receptor may influence ND liability.

Using linkage information to weight a genome-wide association of bipolar disorder.

Issues of multiple-testing and statistical significance in genomewide association studies (GWAS) have prompted statistical methods utilizing prior data to increase the power of association results. Using prior findings from genome-wide linkage studies on bipolar disorder (BPD), we employed a weighted false discovery approach (wFDR; [Roeder et al. 2006. Am J Hum Genet 78(2): 243­252]) to previously reported GWAS data drawn from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD). Using this method, association signals are up or down-weighted given the linkage score in that genomic region. Although no SNPs in our sample reached genome-wide significance through the wFDR approach, the strongest single SNP result from the original GWAS results (rs4939921 in myosin VB) is strongly up-weighted as it occurs on a linkage peak of chromosome 18. We also identify regions on chromosome 9, 17, and 18 where modestly associated SNP clusters coincide with strong linkage scores, implicating them as possible candidate regions for further analysis. Moving forward, we believe the application of prior linkage information will be increasingly useful to future GWAS studies that incorporate rarer variants into their analysis.

SNPs in CHRNA6 and CHRNB3 are associated with alcohol consumption in a nationally representative sample.

The CHRNA6 and CHRNB3 genes have been associated with nicotine dependence and early subjective response to nicotine. Here we present evidence, using a nationally representative sample of adults, that this region is also associated with alcohol behaviors. Six SNPs (single nucleotide polymorphisms) spanning the CHRNB3/A6 genes were analyzed using the statistical genetics software FBAT-PC, which allows one to examine a collection of multiple phenotypes to generate a maximally heritable composite phenotype for each SNP. The six SNPs were tested using FBAT-PC including four alcohol phenotypes: average number of drinks, blackouts, total number of DSM-IV abuse and dependence symptoms endorsed, and quit attempts. Three SNPs in CHRNA6 (rs1072003, P = 0.015; rs892413, P = 0.0033 and rs2304297, P = 0.012) and one SNP in CHRNB3 (rs13280604, P = 0.0053) were associated with a composite of the alcohol phenotypes. The association was primarily driven by the average number of drinks.

Whole-genome association study of bipolar disorder.

We performed a genome-wide association scan in 1461 patients with bipolar (BP) 1 disorder, 2008 controls drawn from the Systematic Treatment Enhancement Program for Bipolar Disorder and the University College London sample collections with successful genotyping for 372,193 single nucleotide polymorphisms (SNPs). Our strongest single SNP results are found in myosin5B (MYO5B; P=1.66 x 10(-7)) and tetraspanin-8 (TSPAN8; P=6.11 x 10(-7)). Haplotype analysis further supported single SNP results highlighting MYO5B, TSPAN8 and the epidermal growth factor receptor (MYO5B; P=2.04 x 10(-8), TSPAN8; P=7.57 x 10(-7) and EGFR; P=8.36 x 10(-8)). For replication, we genotyped 304 SNPs in family-based NIMH samples (n=409 trios) and University of Edinburgh case-control samples (n=365 cases, 351 controls) that did not provide independent replication after correction for multiple testing. A comparison of our strongest associations with the genome-wide scan of 1868 patients with BP disorder and 2938 controls who completed the scan as part of the Wellcome Trust Case-Control Consortium indicates concordant signals for SNPs within the voltage-dependent calcium channel, L-type, alpha 1C subunit (CACNA1C) gene. Given the heritability of BP disorder, the lack of agreement between studies emphasizes that susceptibility alleles are likely to be modest in effect size and require even larger samples for detection.

Further evidence for LBP-1c/CP2/LSF association in Alzheimer's disease families.

OBJECTIVES: Several studies suggested chromosome 12 harbours an Alzheimer's disease (AD) risk factor gene. Significant association of a single nucleotide polymorphism (SNP) in the 3' UTR of transcription factor CP2 (LBP-1c/CP2/LSF or TFCP2) at 12q13 was reported in three independent case-control studies, but no family based analyses have been performed to date. METHODS: Genotypes for three SNPs were generated in two independent AD family samples. A meta-analysis on all published case-control studies was also performed. RESULTS: The A allele of the 3' UTR SNP was associated with increased risk for AD in one sample (odds ratio (OR) 2.1, 95% confidence interval (95% CI) 1.1 to 4.3), but not in the other, possibly due to low power. Haplotype analyses showed that this allele is part of a putative risk-haplotype overtransmitted to affected individuals in one sample and in both samples combined. Meta-analysis of the previously associated 3' UTR SNP showed a trend towards a protective effect of the A allele in AD (OR 0.73, 95% CI 0.5 to 1.1). CONCLUSIONS: This is the first study to examine LBP-1c/CP2/LSF in AD families, and the fifth to independently show significant association. While our results support a role of this gene in AD pathogenesis, the direction of the effect remains uncertain, possibly indicating linkage disequilibrium with another variant nearby.

Opioid-dependent effects of inescapable shock on escape behavior and conditioned fear responding are mediated by the dorsal raphe nucleus.

Manipulations of the dorsal raphe nucleus (DRN) modulate the behavioral effects of exposure to inescapable shock (IS). Opiate agonists and antagonists also influence the impact of IS, but the role of the DRN in mediating these effects is unknown. The opiate antagonist naltrexone micro-injected into the region of the DRN immediately prior to IS prevented both the escape deficit and the enhancement of fear conditioning that occur 24 h later. Intra-DRN naltrexone administered at the time of later behavioral testing reduced, but did not eliminate, these effects of prior IS. Conversely, the opiate agonist morphine, in combination with a subthreshold number of 20 IS trials, induced an escape deficit and enhanced conditioned fear 24 h later. Microinjections of naltrexone into the dorsolateral periaqueductal gray area did not alter the effects of IS and electrolytic lesions of the DRN prevented the effect of the morphine-20 IS trial combination. The role of opioids in mediating the behavioral effects of IS is discussed.

Activation of serotonin-immunoreactive cells in the dorsal raphe nucleus in rats exposed to an uncontrollable stressor.

The dorsal raphe nucleus (DRN) and its serotonergic terminal regions have been suggested to be part of the neural substrate by which exposure to uncontrollable stressors produces poor escape responding and enhanced conditioned fear expression. Such stressor exposure is thought to selectively activate DRN serotonergic neurons in such a way as to render them transiently sensitized to further input. As a result of this sensitized state, behavioral testing procedures are thought to cause excess serotonergic activity in brain regions that control these behaviors. The present studies were conducted to investigate activity in the DRN following exposure to escapable and yoked, inescapable tailshock. Neural activity was characterized using immunohistochemistry to detect the immediate early gene product Fos in serotonin-immunoreactive cells in the DRN. Inescapable tailshock led to greater serotonergic neural activity than did escapable tailshock, supporting the hypothesis that uncontrollable stressors preferentially activate serotonergic neurons in the DRN.