Intermediate Phenotypes for Alcoholism and Whole Genome Linkage Scan

酗酒的遗传率在男性和女性中均为40-60%，然而，与其他复杂的精神疾病一样，很难确定致病基因。中间表型是相关的生物学性状，可能受到较少基因变异的影响，并可能介导疾病的不同方面。我们正在研究的酒精中毒的中间表型包括维度焦虑（避免伤害），静息EEG表型和事件相关电位（ERP）。我们有三个大型电生理中间表型数据集：247名美国白人，365名酗酒患病率高的平原美洲印第安人和198名酗酒患病率低的东南美洲印第安人。与密歇根大学的Zubietta博士和NIDA的Stein博士合作，我们还研究了成像数据（fMRI和正电子发射断层扫描（PET））作为成瘾相关表型的中间表型。 在平原印第安人样本中进行的全基因组连锁扫描没有发现酗酒的连锁信号。然而，染色体（chr）5上α、β和θ EEG功率的连锁峰收敛，LOD评分为3.5。促肾上腺皮质激素释放激素结合蛋白（CRHBP）基因位于会聚连锁峰的顶点。CRHBP与压力和成瘾有关。随后的分析表明，CRHBP单核苷酸多态性和单倍型与平原印第安人和美国高加索人的α EEG功率显著相关。此外，相同的CRHBP SNP与平原印第安人的焦虑症和美国高加索人的酒精使用障碍显著相关（以诺等人，2008）。这些结果表明CRHBP在包括酒精中毒在内的压力相关疾病中可能发挥作用。事实上，我们最近已经表明，在具有物质依赖的非裔美国男性样本中，相同的远端CRHBP SNP预测了那些暴露于严重童年创伤的个体的自杀行为（Roy等人，2012）。 CRHBP通过几个单倍型块与相邻基因缓冲，表明功能基因座可能位于该基因或其周围。我们已经证明了脑中存在替代CRHBP同种型，其中末端外显子被剪接掉，有利于两个替代外显子，导致肽序列的变化，这可能影响蛋白质折叠和稳定性，从而改变CRH结合亲和力。目前正在进行功能研究。 在chr 22上发现θ EEG功率的连锁峰，LOD评分为3.2。在第4、10和11次给药时存在提示性峰（LOD = 2.2 - 2.5）。在chr 11上的连锁峰的顶点处有三个候选基因：5-羟色胺受体3A和3B（HTR 3A和HTR 3B）和DRD 2。我们发现，在平原印第安人和美国高加索人中，HTR 3B和EEG α功率之间存在显著相关性，并且与芬兰高加索人中的反社会酒精中毒存在显著相关性（Ducci et al，2009）。此外，在药物滥用的非裔美国男性样本中，我们发现功能性HTR 3B SNP rs 1176744与酒精依赖相关（以诺等人，2011）。我们的研究表明，中间表型是特别有用的，以确定基因的酗酒在人口中的高患病率的这种疾病。 最近与Zubietta博士的合作研究表明，仅在女性中，催产素基因的遗传变异与压力诱导的多巴胺激活（通过PET测量）有关，这是酗酒的脆弱因素（Love et al，2012）。此外，编码应激反应CRH 1受体的CRHR 1基因的变异与对情绪刺激的神经反应（通过fMRI测量）的差异相关（Hsu et al，2012），这可能表明易受应激相关疾病（包括酗酒）的影响。最后，在与NIDA的Stein博士团队的合作中，我们已经证明尼古丁和COMT Val 158 Met基因型在奖赏处理过程中调节皮质纹状体网络的激活（通过fMRI测量）（Lee等人，提交）。 前题为“脑电图和事件相关电位的遗传学研究”和“与酒精中毒有关的脑电图和ERP特征的遗传学研究”。

The heritability of alcoholism is 40-60% in both men and women however, as in other complex psychiatric diseases it has proved difficult to identify causative genes. Intermediate phenotypes are associated biological traits that may be influenced by variation at fewer genes and may mediate different aspects of the disease. The intermediate phenotypes for alcoholism that we are studying include dimensional anxiety (harm avoidance), resting EEG phenotypes and event-related potentials (ERPs). We have three large electrophysiological intermediate phenotype datasets: 247 U.S. Caucasians, 365 Plains American Indians with a high prevalence of alcoholism and 198 Southeastern American Indians with a low prevalence of alcoholism. In collaboration with Dr Zubietta from the University of Michigan and Dr Stein from NIDA we are also studying imaging data (fMRI and positron emission tomography (PET)) as an intermediate phenotype for addiction-related phenotypes. A whole genome linkage scan in the Plains Indian sample did not identify a linkage signal for alcoholism. However, there was a convergence of linkage peaks for alpha, beta and theta EEG power on chromosome (chr) 5 with LOD scores of 3.5. The gene for corticotropin releasing hormone binding protein (CRHBP) was located at the apex of the convergent linkage peaks. CRHBP is implicated in stress and addiction. Subsequent analyses showed that CRHBP SNPs and haplotypes were significantly associated with alpha EEG power in the Plains Indians and also the U.S. Caucasians. Moreover, the same CRHBP SNPs were significantly associated with anxiety disorders in the Plains Indians and alcohol use disorders in the U.S. Caucasians (Enoch et al, 2008). These results suggest a likely role for CRHBP in stress-related disorders including alcoholism. Indeed, we have recently shown that in a sample of African American men with substance dependence, the same distal CRHBP SNPs predicted suicidal behavior in those individuals who had been exposed to severe childhood trauma (Roy et al, 2012). CRHBP is buffered from adjacent genes by several haplotype blocks indicating that a functional locus is likely to reside within this gene or its environs. We have demonstrated the presence of an alternative CRHBP isoform in brain in which the terminal exon is spliced out in favor of two alternative exons resulting in a change in peptide sequence that might affect protein folding and stability resulting in altered CRH binding affinity. Functional studies are currently underway. A linkage peak for theta EEG power with a LOD score of 3.2 was found on chr 22. There were suggestive peaks (LOD = 2.2 to 2.5) on chrs 4, 10 and 11. There are three candidate genes at the apex of the linkage peak on chr 11: serotonin receptors 3A and 3B (HTR3A and HTR3B) and DRD2. We found a significant association between HTR3B and EEG alpha power in both the Plains Indians and U.S. Caucasians and with antisocial alcoholism in Finnish Caucasians (Ducci et al, 2009). Moreover, in a sample of African American men with substance abuse, we found that a functional HTR3B SNP rs1176744 was associated with alcohol dependence (Enoch et al, 2011). Our studies have shown that intermediate phenotypes are particularly useful for identifying genes for alcoholism in populations with a high prevalence of this disease. Recent collaborative studies with Dr Zubietta have revealed that in women only, genetic variation in the oxytocin gene is associated with stress-induced dopamine activation (measured by PET), a vulnerability factor for alcoholism (Love et al, 2012). Also, variation in the CRHR1 gene that encodes the stress-response CRH1 receptor was associated with differences in neural responses (measured by fMRI) to emotional stimuli (Hsu et al, 2012) that may indicate vulnerability to stress-related disorders including alcoholism. Finally, in a collaboration with Dr Stein's group from NIDA we have shown that nicotine and COMT Val158Met genotype regulate activation (measured by fMRI) in a cortico-striatal network during reward processing (Lee et al, submitted). Formerly titled "Genetic studies of the electroencephalogram and event-related potentials" and "Genetic studies of EEG and ERP traits related to alcoholism".