Identification of a causative gene for autosomal recessive familial amyotrophic lateral sclerosis

本研究旨在通过对候选区域基因的连锁分析和突变分析，寻找常染色体隐性遗传性家族性肌萎缩侧索硬化症(AR-FALS)的致病基因。对三个AR-FAL家系的纯合性图谱显示，在所有家系中有一个候选区域重叠。针对位于候选区域的40个基因的全部外显子，设计了基因组聚合酶链式反应的特异性引物。此外，还设计了用于检测拷贝数变异的阵列比较基因组杂交(ARRAY-CGH)系统。然而，使用这些系统的突变分析并没有发现新的突变。然后，对家系大小最大的一个家系进行了常染色体隐性遗传模式允许复合杂合突变的连锁分析，发现候选区域总长度为470兆碱基。对该家系的先证者进行外显子组分析和全基因组测序，发现了一个新的非同义纯合子突变，该突变没有在公共数据库中登记，包括DBSNP、NHL-ESP或1000基因组。这种突变在家庭成员中是共分离的，在461名日本对照组中没有发现。然而，对排除已知致病基因突变的20个FAL家系的突变分析，没有发现该基因的纯合子或复合杂合性突变。对其他FAL家系的突变分析被认为是必要的，以确定已鉴定突变的致病性。

This study aims for the identification of causative genes in autosomal-recessive familial amyotrophic lateral sclerosis (AR-FALS) through a linkage analysis and mutational analysis of genes located in the candidate regions. A homozygosity mapping of three AR-FALS pedigrees revealed a candidate region overlapped among all the pedigrees. Specific primers for genomic PCR were designed for all the exons of 40 genes located in the candidate region. In addition, an array comparative genomic hybridization (array-CGH) system was designed for the detection of copy-number variations. Mutational analysis employing these systems, however, did not reveal a novel mutation. Then, a linkage analysis with the assumption of autosomal recessive mode of inheritance allowing compound heterozygous mutations was performed in one of the pedigrees with the largest pedigree size, which revealed candidate regions spanning a total length of 470 mega-bases. An exome analysis and a whole genome sequencing con ducted for a proband in the pedigree revealed an novel nonsynonymous homozygous mutation which was not registered in public databases including dbSNP, NHL-ESP or 1000 genomes. The mutation was co-segregated among family members and not found in 461 Japanese controls. Mutational analysis for 20 FALS pedigrees in whom mutations in known causative genes were excluded, however, did not reveal homozygous or compound heterozygous mutations in the gene. Mutational analysis for additional FALS pedigrees was considered to be necessary to establish the pathogenicity of the identified mutation.