精神分裂症是一种复杂的重性精神疾病，病因不清且功能预后差。Lancet于2017年9月发布了全球195个国家的328种疾病负担调查报告。报告指出精神分裂症是中国第九大疾病负担源。有数据显示，我们每年用于精神分裂症治疗的相关费用高达数百亿。加之，该病病程迁延，患者存在多方面障碍，这对患者和家庭以及社会都是沉重的负担。因此，研究其发病机制具有重大的现实意义。 Sullivan等人（2003）对在此之前的双生子研究进行了荟萃分析，结果提示精神分裂症遗传度约为81%。近期，Hilker等人（2018）完成的一项迄今为止最大规模的双生子研究也指出精神分裂症遗传度高达79%。这些证据均提示进行精神分裂症分子遗传学研究寻找其易感基因的重要性。近十年迅速发展起来的大样本全基因组关联研究（GWAS）在精神分裂症中获得了广泛开展。最近一项来自PGC（Psychiatric Genomics Consortium）的研究使用GWAS数据进行估计，发现单核苷酸多态性（Single Nucleotide Polymorphisms，SNP）可以解释23%的精神分裂症易感变异。虽然由此引发了人们关于缺失的遗传度（Missing Heritability）的讨论，但也同时提示了SNP研究的重大意义。 在所有关于精神分裂症的GWAS中，第一个被报道也是被重复次数最多的精神分裂症风险基因多态性是ZNF804A基因rs1344706多态性。但该风险基因的功能尚不清楚。本论文在“基因-脑-行为-疾病”大框架的指导下开展系列研究，综合使用认知心理行为测查、磁共振脑功能激活区检测、基于种子点的局部脑区间功能连接、基于体素水平的全脑功能网络、基于体素水平的脑形态学测量、脑区间白质纤维连接重建等技术，来探讨ZNF804A基因rs1344706多态性与精神分裂症相关的脑机制。本论文共包括以下四个研究。 研究一:ZNF804A基因rs1344706多态性与精神分裂症及其认知障碍的相关性研究。自ZNF804A基因rs1344706多态性作为首个可经受全基因组多重比较校正的精神分裂症易感基因多态性被报道以来，多个欧洲样本均重复了二者之间的相关性。但这种相关性在中国汉族人群中的研究结果却很不一致。本研究首先使用1105例精神分裂症患者和916例健康受试者对rs1344706与精神分裂症的关联性进行分析。结果显示在中国汉族人群中二者显著相关（χ2 = 8.62；P = 0.013）。接下来，我们还进一步对精神分裂症患者和健康对照的认知行为数据（包括测查工作记忆能力的N-back和DPX任务以及测查执行控制功能的ANT和Stroop任务）进行了研究，但并未发现rs1344706多态性与上述认知功能的相关性（所有P > 0.05）。 研究二:ZNF804A基因rs1344706多态性对脑局部功能连接的影响。既往针对ZNF804A基因rs1344706多态性的磁共振研究中重复率最高的研究结果是它虽然与N-back任务期间的脑激活不相关，但与N-back任务期间右侧背外侧前额叶（DLPFC）与左侧海马（HF）之间的功能连接显著相关。然而，一方面这一相关性仅存在于N-back任务态，在其它任务态或静息态中相关性消失，另一方面，右侧DLPFC和左侧HF之间并无直接白质纤维结构连接。因此，本研究使用fMRI和DTI数据联合分析的方法，希望找到在各种模态数据中均与rs1344706显著相关的局部连接。本研究共采集了87例健康受试者的多模态磁共振数据。首先，以右侧DLPFC为种子点，在N-back任务态fMRI数据中重复出了rs1344706多态性与右侧DLPFC-左侧HF功能连接之间的相关性（Alphasim校正后P = 0.013）。随后，重建右侧DLPFC和左侧HF之间的白质纤维结构连接，共包括三个子连接：右侧DLPFC-前扣带皮层/内侧前额叶（ACC/MPFC）、ACC/MPFC-后扣带皮层/楔前叶（PCC/PCU）和PCC/PCU-左侧HF。提取每个子连接的平均各向异性分数（FA）后发现rs1344706与PCC/PCU-左侧HF子连接的FA值显著相关（P = 0.011），风险等位基因纯合子（AA）的FA值减低。最后，以左侧海马作为种子点，分析N-back任务态和静息态fMRI数据发现，风险等位基因纯合子（AA）在左侧HF-PCC/PCU的功能连接强度同样显著减低（N-back任务态fMRI，Alphasim校正后P = 0.001；静息态fMRI，Alphasim校正后P = 0.01）。综上所述，左侧HF-PCC/PCU的功能和结构“失连接”是rs1344706多态性与精神分裂症相关的可能的脑机制之一。 研究三：ZNF804A基因rs1344706多态性对脑功能连接网络的影响。以往的多项研究均采用基于种子点的功能连接计算方法并一致地发现rs1344706多态性与特定脑区之间的功能连接显著相关。本论文的研究二也得到相似结论。然而，这种计算方法会受到所选取的种子点的影响，因而存在很大局限性。研究三使用图论度中心度指标构建全脑功能连接网络，并在全脑范围内无偏地寻找ZNF804A基因rs1344706多态性发挥作用的靶向脑区。共计55例精神分裂症患者和137例健康受试者的静息态fMRI数据进入到最后的分析。对全脑全距离脑网络的分析发现楔前叶（PCU）存在显著的rs1344706基因型×诊断交互作用（FWE校正后P < 0.001）。精神分裂症组中rs1344706风险等位基因纯合子（AA）携带者PCU区域的全距离度中心度指标升高（FWE校正后P = 0.042），健康对照组中未发现二者显著的相关性（FWE校正后P > 0.05）。进一步根据解剖距离划分为长距离和短距离两种全脑连接网络，并将分析局限在PCU后，只在短距离连接中发现该区域存在显著的rs1344706基因型×诊断交互作用（FWE校正后P < 0.001）。具体表现为精神分裂症组中rs1344706风险等位基因纯合子（AA）携带者PCU区域的短距离度中心度指标升高（FWE校正后P < 0.001），健康对照组中未发现二者显著的相关性（FWE校正后P > 0.05）。在长距离连接中未发现类似结果。研究三的这一结果阐释了rs1344706多态性对脑功能连接网络的贡献，并进一步提示PCU是rs1344706发挥作用的关键大脑节点。这对我们了解该风险基因在精神分裂症“功能失连接”中的作用具有重要意义。 研究四：ZNF804A基因rs1344706多态性对大脑灰质结构形态的影响。既往研究已经提示脑功能连接与脑灰质体积之间的密切关系。为了佐证本论文研究三的结果，本研究使用基于体素的形态学测量方法（VBM）对66例精神分裂症患者和179例健康受试者的结构磁共振图像进行分析。我们同样在PCC/PCU区域发现显著的rs1344706基因型×诊断交互作用（GRF校正后P < 0.05）。精神分裂症风险等位基因纯合子（AA）在PCC/PCU区域的灰质体积减小（GRF校正后P < 0.05）。而在健康对照组中却获得相反的相关性，即风险等位基因纯合子（AA）在PCC/PCU区域的灰质体积增大（GRF校正后P < 0.05）。该研究再次证实了PCC/PCU在rs1344706与精神分裂症相关性中的重要作用。 综上所述，本研究秉承“基因-脑-行为-疾病”的研究框架，通过在行为水平和脑影像水平对ZNF804A基因rs1344706多态位点进行的系列性研究阐明，PCC/PCU区域的功能和结构异常是rs1344706与精神分裂症显著相关的重要脑机制之一。

Schizophrenia is a complex and severe mental illness, however its etiology was still unknown. Schizophrenia poses a heavy burden on patient, his families and society. Data shows that the annual costs associated with the treatment of schizophrenia are as high as tens of billions. Therefore, it is of great practical significance to study the pathogenesis of schizophrenia. Sullivan and his colleagues’ meta-analysis on more than 12 twin studies have estimated heritability of schizophrenia at about 81%, which indicated an importance of molecular genetic study in elucidating the etiology of schizophrenia. Recently, many GWAS has been done in schizophrenia across the whole world. A study did by Psychiatric Genomics Consortium estimated that common single nucleotide polymorphisms (SNPs) alone could explain about 23% of the variance in schizophrenia liability. Although most heritability of schizophrenia remains unexplained (it was called “missing heritability”), the importance of SNP study was undeniable. In the GWAS of schizophrenia, a SNP (rs1344706) within ZNF804A (zinc-finger protein 804A) gene was reported to be the first one that was significantly associated with schizophrenia after whole-genome multiple comparison correction. However, the mechanism underlying this association was still unknown. This Thesis aimed to investigate the brain mechanisms of rs1344706. Following the framework of the “Gene-Brain-Behavior-Disease”, this thesis conducted a series of studies involving comprehensive technology within the field of cognitive neuroscience and magnetic resonance imaging (brain activation detection, seed-based functional connectivity, and voxel-based function network, Voxel-based morphometry, and fiber tracking). This thesis included the following four studies. Study 1. Association of ZNF804A Gene rs1344706 Polymorphism with Schizophrenia and Its Cognitive Impairment. Since a SNP (rs1344706) within ZNF804 gene was reported to be the first one that was significantly associated with schizophrenia after whole-genome multiple comparison correction, many European samples replicated the same association. However, the association in Chinese Han population are inconsistent. In this study, we tried to replicate this association within 1105 schizophrenic patients and 916 healthy controls. The results showed significant associaiton between rs1344706 and schizophrenia (χ2 = 8.62, P = 0.013). Next, we tested the association between rs1344706 and cognitive functions as measured by four tasks. However, none of significant association was found for any task performance (all P > 0.05). So, this study suggested that rs1344706 may be a risky polymorphism in the genetic etiology of schizophrenia although did not support the association between rs1344706 and cognitive functions. Study 2. Effect of rs1344706 in the ZNF804A Gene on the Connectivity between the Hippocampal Formation and Posterior Cingulate Cortex/Precuneus. Previous fMRI studies in healthy controls have repeatedly shown an association of rs1344706 with the functional connectivity between the right dorsolateral prefrontal cortex (DLPFC) and the left hippocampal formation (HF) during a N-back task. However, on the one side, this association existed only during N-back task however not during other task or resting state; On the other side, there is no direct fiber connections between the right DLPFC and the left HF. This study used a combined analysis on both fMRI (for N-back fMRI, 81 healthy controls were involved; for resting-state fMRI, 84 healthy controls were involved) and DTI data (87 healthy controls were involved) to find the connections that were affected by rs1344706 but not state-dependent. First, using the right DLPFC as seed, we replicated the association between rs1344706 and the right DLPFC-left HF functional connectivity during N-back task (corrected P = 0.013). Next, we reconstructed fiber connections between the right DLPFC and the left HF using our DTI data, which included three subconnections: between the right DLPFC and the anterior cingulated cortex/medial prefrontal cortex (ACC/MPFC), between the ACC/MPFC and the posterior cingulate cortex/precuneus (PCC/PCU), between the PCC/PCU and the left HF. We extracted the fractional anisotropy (FA) of each subconnection and found that rs1344706 only showed significant association with the mean FA of the left HF-PCC/PCU tract (P = 0.011). Finally, we analyzed the fMRI data on both of the N-back task and the resting state and consistently found significant associations between rs1344706 and left HF-PCC/PCU functional connectivity (for N-back, corrected P = 0.001; for resting state, corrected P = 0.01). Taken together, the disconnectivity (both functional and structural) between the left HF and the PCC/PCU seems to be an important brain mechanism for the association between rs1344706 and schizophrenia. Study 3. Effect of rs1344706 in the ZNF804A Gene on the Brain Network. Recent studies have linked rs1344706 to functional connectivity between specific brain regions using seed-based functional connectivity, which was also supported by our Study 2. One limitation of the previous functional connectivity studies is that they relied on a priori selection of seeds. No study thus far has examined the role of this SNP in the entire functional connectome. In this study, we test the role of rs1344706 polymorphism in the whole-brain voxel-wise functional connectome during the resting state. 137 healthy controls and 55 schizophrenia patients were involved in our final data analysis. In our whole-brain analysis, we found a significant interaction effect of genotype × diagnosis at the precuneus (PCU) (corrected P < 0.001). We found significantly increased degree centrality within PCU in the risk allele homozygotes (AA genotype) in schizophrenia (corrected P = 0.042) however not in healthy controls (corrected P > 0.05). When we subdivided the degree centrality network according to anatomical distance, we only found a significant interaction effect of genotype × diagnosis at the PCU in the short-range degree centrality network (corrected P < 0.001 ) however not in the long-range degree centrality network (corrected P > 0.05). The risk allele homozogotes (AA genotype) again showed significantly increased degree centrality within the PCU in schizophrenia only (corrected P < 0.001). No significant association was find in healthy controls (corrected P > 0.05). Our results suggested that PCC/PCU may be an important brain hub underlying the association between rs1344706 and schizophrenia. Study 4. Effect of rs1344706 in the ZNF804A Gene on Brain Morphology. Previous studies have suggested the close relationship between functional connections and gray matter volume in brain. In order to support the results of Study 3, we analysed effects of rs1344706 on grey matter using voxel-based morphometry (VBM) in high-resolution T1-weighted magnetic resonance imaging scans of 66 schizophrenia patients and 179 healthy controls. We limited our analysis to the PCC/PCU region and found a significant interaction effect of genotype × diagnosis (corrected P < 0.05) at PCC/PCU. In the schizophrenia patients, we observed significantly decreased gray matter volume within PCC/PCU in the risk allele homozygotes (AA genotype) comparing with non-risk allele carriers (CC/CA genotype) (corrected P <0.05). However, reversed association was observed in healthy controls (corrected P <0.05). So, this VBM analysis also supported a significant role of PCC/PCU in the mechanisms underlying the association between rs1344706 and schizophrenia. In summary, this thesis followed the “gene-brain-behavior-disease” research framework. Through a series of brain imaging toward ZNF804A single nucleotide polymorphism rs1344706, it was clarified that functional and structural abnormalities of the PCC/PCU region may be important brain mechanisms linking rs1344706 polymorphism and schizophrenia.