Studies Of Hereditary Neurological Disease: Disease Gene Identification

这项研究计划的目的是调查遗传性神经疾病的原因，目的是为这些疾病开发有效的治疗方法。遗传外展计划允许识别和描述患有遗传性神经疾病的患者和家庭的特征。过去一年的具体研究成果包括(1)在马里发现了一种新的远程共济失调突变，(2)在遗传性痉挛截瘫患者(SPG43)中发现了C19orf12的突变，(3)在Cowchock综合征(CMTX4)患者中发现了AIFM1的突变，(4)制定了夏科-玛丽-图斯病的新的基因诊断指南，以及(5)在轴索性神经病患者中发现了组氨酸氨酰tRNA合成酶(HARS)的序列变体。 共济失调毛细血管扩张症是一种罕见的儿童常染色体隐性遗传性疾病，其特征是进行性小脑性共济失调、毛细血管扩张和免疫缺陷，由ATM基因突变引起。这种疾病在世界各地都有报道，但来自非洲的报道很少，而且往往仅限于临床描述。我们描述了一个有父母血缘关系的马里家庭，十分之三的儿童出现小脑症状。对ATM基因的遗传分析确定了一种新的纯合子单核苷酸替代，预测了氨基酸替代V2662D。V2662残基位于预测的ATP结合区，在广泛的脊椎动物物种中保守。此外，在种族匹配的对照组中没有发现这种酸性变化，这表明这种突变可能是有害的。 Charcot Marie Tooth病(CMT)是指遗传性周围神经病变。虽然已发现四个基因(PMP22、GJB1、MPZ、Mfn2)导致了90%以上的CMT，但至少有51个基因和基因座在突变时导致CMT，这给临床医生寻找家系的基因亚型带来了困难。我们描述了CMT的经典特征和最常见的CMT亚型的特征，以及缩小可能亚型的方法。确定了CMT人群特有的心理社会问题。其结果是出版了一本关于CMT特定遗传咨询的包容性出版物。 我们确定了SPG43的遗传基础，这是一种我们之前在两个马里姐妹中描述的进行性遗传性痉挛截瘫的形式。外显子序列分析显示，C19orf12存在一个纯合子错义变异(A63P)，该基因最近与神经退行性变伴脑铁蓄积(NBIA)有关。随后在一个具有NBIA特征的巴西家庭中也发现了相同的突变，我们发现了另一名具有三核苷酸缺失(G66del)的NBIA患者。单倍型分析显示，A63P突变具有共同的来源，但MRI扫描显示，马里SPG43受试者没有脑铁沉积。这些SPG43和NBIA变异体的异源表达导致C19orf12的亚细胞分布发生类似的变化。本文报道的SPG43和NBIA变异体以及在NBIA患者中报道的最常见的C19orf12错义突变在C19orf12的一个高度保守的、延伸的疏水结构域中被发现，这突显了该结构域的功能重要性。 Cowchock综合征(CMTX4)是一种进展缓慢的X连锁隐性疾病，伴有轴突神经病变、耳聋和认知障碍。该疾病位点先前被定位在染色体Xq24-Q26上的11 cM区域。对最初描述的家系中的一个受影响个体的外显子组测序发现了凋亡抑制因子(AIFM1)的错义变化(E493V)。这种变化是高度保守的残基，并与该家族的表型共分离。AIF是一种依赖FAD的NADH氧化酶，被输入到线粒体中。在细胞凋亡的作用下，N-末端的跨膜连接物被切割，产生一个可溶片段，释放到胞浆中，然后运输到细胞核，在那里它触发caspase不依赖于caspase的凋亡。另一个AIFM1突变，R201del，最近被认为与两个婴儿的严重线粒体脑肌病有关，因为它损害了氧化磷酸化。我们发现的E493V突变改变了AIF蛋白的氧化还原特性，并通过细胞凋亡导致细胞死亡增加，而不影响呼吸链复合体的活性。我们的发现扩大了AIF相关疾病的范围，并为AIFM1突变的影响提供了洞察力。 氨基酰-tRNA合成酶是一种普遍表达的酶，负责将氨基酸连接到同源的tRNA分子上。编码ARS的四个基因的突变与遗传性周围神经病变和轴突病理有关，这表明所有ARS基因都是相关表型患者的相关疾病候选。我们公布了在大量周围神经病患者中进行组氨酰-tRNA合成酶(HARS)基因突变筛查的结果。这些工作揭示了一种罕见的错义变体(R137G)，它位于高度保守的氨基酸，在酵母互补分析中评估时代表功能丧失的等位基因，当在蠕虫模型中表达时对神经元有毒。除了一名周围神经病患者外，还通过全基因组外显子组测序在三个个体中检测到R137G HARS。这些发现表明，HARS是第五个与轴索周围神经病相关的ARS基因座。

The purpose of this research program is to investigate the causes of hereditary neurological diseases, with the goal of developing effective treatments for these disorders. A genetic outreach program allows the identification and characterization of patients and families with hereditary neurological diseases. Specific research accomplishments in the past year include (1) identification of a novel ataxia telangestasia mutation in Mali, (2) identification of mutations in C19orf12 in patients with hereditary spastic paraplegia (SPG43), (3) identification of mutation in AIFM1 in patients with Cowchock syndrome (CMTX4), (4) development of new guidelines for genetic diagnosis of Charcot-Marie-Tooth disease, and (5) identification of a sequence variant in histidine aminoacyl tRNA synthetase (HARS) in a patient with axonal neuropathy. Ataxia telangiectasia is a rare, autosomal recessive disorder of childhood characterized by progressive cerebellar ataxia, telangiectasia, and immune defects, and caused by mutations in the ATM gene. The disease has been reported worldwide, but reports from Africa are rare and often limited to clinical description. We described a Malian family with parental consanguinity and three out of ten children presenting with cerebellar symptoms. Genetic analysis of the ATM gene identified a novel homozygous single nucleotide substitution predicting the amino acid substitution V2662D. The V2662 residue lies in a predicted ATP binding domain and is conserved across a broad range of vertebrate species. In addition, this acid change was not found in ethnically matched controls, suggesting that the mutation is likely deleterious. Charcot Marie Tooth disease (CMT) encompasses the inherited peripheral neuropathies. While four genes have been found to cause over 90% of genetically identifiable causes of CMT (PMP22, GJB1, MPZ, MFN2), at least 51 genes and loci have been found to cause CMT when mutated, creating difficulties for clinicians to find a genetic subtype for families. We described the classic features of CMT and the characteristic features of the most common subtypes of CMT, as well as methods for narrowing down the possible subtypes. Psychosocial concerns particular to the CMT population were identified. The result was an inclusive publication for CMT-specific genetic counseling. We identified the genetic basis for SPG43, a form of progressive hereditary spastic paraplegia we previously described in two Malian sisters. Exome sequencing revealed a homozygous missense variant (A63P) in C19orf12, a gene recently implicated in neurodegeneration with brain iron accumulation (NBIA). The same mutation was subsequently also found in a Brazilian family with features of NBIA, and we identified another NBIA patient with a three-nucleotide deletion (G66del). Haplotype analysis revealed that the A63P mutations have a common origin, but MRI scans showed no brain iron deposition in the Malian SPG43 subjects. Heterologous expression of these SPG43 and NBIA variants resulted in similar alterations in the subcellular distribution of C19orf12. The SPG43 and NBIA variants reported here as well as the most common C19orf12 missense mutation reported in NBIA patients are found within a highly conserved, extended hydrophobic domain in C19orf12, underscoring the functional importance of this domain. Cowchock syndrome (CMTX4) is a slowly progressive X-linked recessive disorder with axonal neuropathy, deafness, and cognitive impairment. The disease locus was previously mapped to an 11 cM region at chromosome Xq24-q26. Exome sequencing of an affected individual from the originally described family identified a missense change (E493V) in apoptosis inhibitory factor (AIFM1). The change is at a highly conserved residue and cosegregated with the phenotype in the family. AIF is an FAD-dependent NADH oxidase that is imported into mitochondria. With apoptotic insults, a N-terminal transmembrane linker is cleaved off, producing a soluble fragment that is released into the cytosol and then transported into the nucleus, where it triggers caspase-independent apoptosis. Another AIFM1 mutation, R201del, has recently been associated with severe mitochondrial encephalomyopathy in two infants by impairing oxidative phosphorylation. The E493V mutation we found alters the redox properties of the AIF protein and results in increased cell death via apoptosis, withhout affecting the activity of the respiratory chain complexes. Our findings expand the spectrum of AIF-related disease and provide insight into the effects of AIFM1 mutations. Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed enzymes responsible for ligating amino acids to cognate tRNA molecules. Mutations in four genes encoding an ARS have been implicated in inherited peripheral neuropathy with an axonal pathology, suggesting that all ARS genes are relevant candidates for disease in patients with related phenotypes. We presented results from a mutation screen of the histidyl-tRNA synthetase (HARS) gene in a large cohort of patients with peripheral neuropathy. These efforts revealed a rare missense variant (R137G) that resides at a highly conserved amino acid, represents a loss-of-function allele when evaluated in yeast complementation assays, and is toxic to neurons when expressed in a worm model. In addition to the patient with peripheral neuropathy, R137G HARS was detected in three individuals by genome-wide exome sequencing. These findings suggest that HARS is the fifth ARS locus associated with axonal peripheral neuropathy.