精神分裂症（Schizophrenia，SCZD；OMIM：181500）是一类以思维和情感缺陷为主要表型的复杂重症精神疾患。患者通常于青少年发病，表现出妄想、幻觉、偏执、思维和语言混乱以及社交障碍等症状。该病在全球人群中的终身发病率高达1%，是严重的全球性公共卫生问题。精神分裂症的发病机制目前尚无定论，一些研究者把它归类于神经系统发育疾病，也有人把其划分为神经递质通路疾病，还有一些研究人员把该病称为线粒体脑病的一种。本文集中从线粒体的角度出发，探讨了线粒体DNA（mitochondrial DNA，mtDNA）以及线粒体相关蛋白与国人精神分裂症发病的相关性。 大脑是人体耗能最多（约消耗人体20~25%左右的能量）且对能量供应最为敏感的器官，线粒体作为细胞的能量工厂，它的功能异常被认为会对大脑相关疾病有着重要的影响。mtDNA作为母系单一传递的遗传物质，编码13个线粒体呼吸链相关蛋白、22个线粒体tRNA和2个线粒体rRNA。临床上也不乏家族史表现出母系遗传特征的精神分裂症家系，提示mtDNA的特定突变可能在疾病的发生过程中起到了影响。我们对1212个湖南汉族精神分裂症患者和1005个湖南汉族无关对照个体进行了mtDNA控制区（D-loop region）测序和单倍型类群（haplogroup）的划分，继而对患者组和对照组单倍型类群的频率分布展开统计分析，结果显示单倍型类群B5a的频率在患者群体中显著升高（P=0.02; odds ratio=1.67; 95% confidence interval=1.09-2.56）。进一步对部分B5a类群的患者进行mtDNA全序列测定，并无发现可能致病的枝端私有变异。对患者组和对照组的B5a类群分别进行年龄估算，发现患者组中B5a类群的分化年龄（18 317±3 271 years before present [YBP] ）比对照组年轻（21 403±5 295 YBP），提示两个B5a群体可能经历了不同的进化历程。经与相关地质历史事件进行比较，发现患者组中B5a类群的分化始于末次盛冰期晚期，彼时北半球正经历太阳曝晒导致的冰川融化和海平面不断上升等气候环境的剧烈变化，因此我们推测在病例-对照分析中观察到B5a类群的频率分布差异是由患者组和对照组对外界气候环境剧烈变化的不同应对导致的。 我们还对10个表现出母系遗传特征的精神分裂症家系进行了研究，对各家系的先证者进行了mtDNA全序列测定，目的在于检测是否有可能的枝端私有致病突变存在。研究结果显示，在其中六个先证者中共发现共13个非同义私有变异、1个线粒体tRNA变异和1个线粒体rRNA变异。经过数据库检索和软件预测，认为其中的m.15395A>G（p.K217E of MT-CYB）存在一定的致病性。而同素异位表达实验显示m.3523A>G（p.T73A of MT-ND1）和m.8536A>G（p.N4D of MT-ATP6）都能显著下调细胞ATP的产率，提示这两个变异可能影响精神分裂症的发病。 NADH脱氢酶（泛醌）黄素蛋白2（NADH dehydrogenase [ubiquinone] flavoprotein 2，NDUFV2）是线粒体复合物I的核心组分之一，之前已有多个关于该基因与精神类疾病的阳性关联报道，我们针对该基因的启动子区域约1kb左右的序列进行测序分析，发现日本人中报道过的与精神分裂症相关的两个SNP位点在中国汉族人群中与该疾病并不存在相关性。结合HapMap的数据分析，提示不一致的关联分析结果可能是由群体遗传结构差异造成的。 综上所述，基于关联分析结果的群体遗传学和进化医学分析，为我们从多角度了解精神分裂症这个复杂重症精神疾患提供了新的视角和思路，亦为从进化医学角度探究疾病的发生发展提供了一个经典范例。并且以上结果显示，在mtDNA与精神分裂症相互关系的遗传模式中，常见疾病-稀有变异假说在我们的样本中显示出更好的适用性，接下来收集更多的具母系遗传特征的精神分裂症家系进行扩大研究，有可能会挖掘到一些高外显和高致病性的枝端私有非同义变异，为该病的临床诊断和临床遗传咨询提供宝贵的基础知识。
其他摘要
Schizophrenia (SCZD; OMIM: 181500) is a worldwide prevalent major psychosis, whose lifetime prevalence estimates reach 1% of world population. It is characterized by a breakdown of thought processes and by poor emotional responsiveness. The onset of schizophrenia usually occurs in young adulthood with typical symptoms like hallucinations, delusions, paranoid behaviorals, disorganized speech and thinking, and significant social or occupational dysfunction. There are many hypotheses for disease mechanism of schizophrenia such as neuro-developmental dysfunction hypothesis, neuro-transmitter hypothesis and schizophrenia is regarded as one of mitochondrial brain disease. In this thesis, we dissected the matrilineal components of well-matched Han Chinese with or without schizophrenia from Hunan Province, China, to discern mtDNA haplogroup, mtDNA private variants and mitochondrial protein effect on this disease. A total of 1212 schizophrenia patients and 1005 matched healthy controls, all of Han Chinese origin, were recruited in Hunan Province, China. We classified haplogroup for each participant based on mtDNA sequence variations. Fisher’s exact test and permutation tests were performed to show the statistical significance. Age estimation and phylogeographic analyses were conducted for the mtDNA haplogroup showing a significant difference between cases and controls. Haplogroup B5a presented a statistical significance between the case and control groups (P=0.02; odds ratio=1.67; 95% confidence interval=1.09-2.56). Age estimation of haplogroup B5a in cases revealed a much younger age (18 317±3 271 years before present [YBP]) than that of controls (21 403±5 295 YBP), which was coincident with the Northern Hemisphere deglaciation at the end of the Last Glacial Maximum. To test whether private/rare mtDNA variant confers to genetic susceptibility of schizophrenia in Han Chinese patients, we sequenced the entire mitochondrial genomes of ten probands from families with a family history and a seemingly maternal inheritance pattern of schizophrenia. Besides the haplogroup-specific variants of each proband, we found thirteen non-synonymous private variants, one mt-tRNA variant, and one mt-rRNA variant in six of the evlven probands. Among these non-synonymous private variants, m.15395A>G in the MT-CYB gene was suggested to be harmful through database retrieving and software prediction. Variants m.8536A>G in the MT-ATP6 gene and m.3523A>G in the MT-ND1 gene were tested to reduce the efficiency of ATP production by the allotopic expression assay. Our results revealed that mitochondrial variants to some extent may be responsible for the maternal inheritance of schizophrenia in certain pedigrees. The NADH-ubiquinone oxidoreductase flavoprotein gene (NDUFV2), which encodes a 24 kD mitochondrial complex I subunit, has been reported to be positively associated with schizophrenia and bipolar disorder in different populations. We genotyped the promoter variants of this gene (rs6506640 and rs1156044) by direct sequencing of 529 unrelated Han Chinese schizophrenia patients and 505 matched controls. Fisher’s Exact test was performed to assess whether these two reported single nucleotide polymorphisms (SNPs) confer susceptibility to schizophrenia in Chinese. Allele, genotype and haplotype comparison between the case and control groups showed no statistical significance, suggesting no association between the NDUFV2 gene promoter variants and schizophrenia in Han Chinese. The role of NDUFV2 played in schizophrenia needs to be further studied. Different racial background and/or population substructure might account for the inconsistent results between studies. In conclusion, we systematically dissected the mitochondrial background influence on schizophrenia from an evolutionary medicine perspective on the basis of association study. This study offered us new insights into complex diseases and provides a paradigm for investigating disease history through an evolutionary medicine point of view. Our results suggested that common disease-rare variant (CDRV) model is more suitable for schizophrenia-mtDNA studies. Future investigation based on more maternal inherited pedigrees would unravel more pathogenic private mutations and provide valuable information for clinical diagnosis and genetic couselling of schizophrenia.
修改评论