Genetics and Epigenetics of Amyotrophic Lateral Sclerosis in Mongolia, Egypt, Germany and China

肌萎缩侧索硬化症(ALS)是一种常见的、进展迅速的神经退行性疾病，累及运动皮质、脑干和脊髓的初级运动神经元。骨骼肌的相关失神经会导致肌肉萎缩、瘫痪和呼吸衰竭死亡。大约5%-10%的ALS患者报告了该病的家族史(FAL)，其中约三分之二是由20多个编码蛋白质的ALS基因中的一个突变所解释的。其余患者被认为是具有多基因和/或环境因果关系的散发性(SALS)。肌萎缩侧索硬化症的遗传学在不同种族和/或地理区域之间并不统一。例如，在欧洲血统的人群中最常见的FALS原因是C9ORF72中的六核苷酸重复扩张，在中国血统的患者中非常罕见，并且是由不同的突变创始人事件引起的。此外，表观遗传机制，如DNA甲基化，与肌萎缩侧索硬化症有遗传联系，变化在中枢神经系统和中枢神经系统外组织中都很明显，如血液样本。考虑到大约三分之一的ALS和大多数SALS患者仍未得到解释，而我们对ALS(Epi)遗传学的了解主要来自欧洲血统的患者，我们建议在研究不足的非欧洲人群中寻找新的基因原因，并定义ALS的强大表观遗传学特征。因此，我们计划对250名ALS患者和来自蒙古和埃及的现有亲属进行全基因组测序。识别候选变异，特别是隐性特征、非编码区变异和结构变异，将得到监测功能后果的血液样本的总RNA测序和有针对性的共分离分析的支持。此外，我们计划从来自蒙古、埃及和德国的100名FALS患者和对照组的血液样本中提取Infinium甲基化史诗阵列。增加遗传背景和环境因素的差异可能有助于区分与疾病相关的原发表观遗传改变和继发改变和/或可能的混杂因素。候选变异和强健的表观遗传学变化将在德国和中国的FALS和SALS患者的独立复制队列中通过有针对性的方法进一步证实/探索。考虑到目前ALS的生物标记物，即血浆和/或脑脊液中不同类型的神经丝，仅限于疾病的症状阶段，推测的表观遗传学发现也将在德国症状前突变携带者队列中得到验证，并测试生物标记物的潜力。此外，将对死后的中枢神经系统组织进行分析，以测试相关组织中血液样本变化的保守性，为推测新的疾病机制提供见解。

Amyotrophic lateral sclerosis (ALS) is a common (lifetime risk ~1/400) and rapidly progressing neurodegenerative disease affecting primary motoneurons of the motor cortex, brain stem and spinal cord. Associated denervation of skeletal muscles results in muscular atrophy, paralysis and death by respiratory failure. Roughly 5-10% of ALS patients report a family history of the disease (fALS) and about 2/3 thereof are explained by mutations in one of more than two dozen protein-coding ALS genes. The remaining patients are considered sporadic (sALS) with polygenic and/or environmental causality. Genetics of ALS is not uniform across different ethnic groups and/or geographical regions. For example, the most frequent cause of fALS in populations of European ancestry, a hexanucleotide repeat expansion in C9ORF72, is very rare in patients of Chinese origin and result from distinct mutational founder events. Additionally, epigenetic mechanisms, e.g. DNA methylation, are genetically linked to ALS, and changes are evident in the CNS but also extra-CNS tissue such as blood samples. Considering that roughly 1/3 of fALS and most sALS patients are still unexplained, and our knowledge of ALS (epi)genetics is mainly derived from patients with European ancestry, we propose to search for novel genic causes in understudied non-European populations, and to define robust epigenetic profiles of ALS. Therefore, we plan whole-genome-sequencing of 250 ALS patients and available relatives from Mongolia and Egypt. Identification of candidate variants, especially recessive traits, variations in non-coding regions and structural variants will be supported by total RNA sequencing from blood samples monitoring functional consequences, and by targeted co-segregation analyses. Furthermore, we plan Infinium Methylation EPIC arrays from blood samples of 100 fALS patients and controls from Mongolia, Egypt and Germany. Increasing the variance of genetic backgrounds and environmental factors may help discriminating primary disease-associated epigenetic changes from secondary alterations and/or possible confounders. Candidate variants and robust epigenetic changes will be further confirmed/explored by targeted approaches in independent replication cohorts of German and Chinese fALS and sALS patients. Considering that current biomarkers for ALS, i.e. different types of neurofilaments in plasma and/or cerebrospinal fluid, are restricted to the symptomatic phase of the disease, putative epigenetic findings will also be validated in a cohort of German presymptomatic mutation carriers and tested for biomarker potential. Additionally, post-mortem CNS tissue will be analyzed to test conservation of changes from blood samples in relevant tissues, providing insights into putatively novel disease mechanisms.