Institut National de la Santé et de la Recherche Medicale (INSERM) U1127, Paris, France.
Centre National de la Recherche Scientifique, Unité Mixte de Recherche (UMR) 7225, Paris, France.
JAMA Neurol. 2018 May 1;75(5):591-599. doi: 10.1001/jamaneurol.2017.5121.
Molecular diagnosis is difficult to achieve in disease groups with a highly heterogeneous genetic background, such as cerebellar ataxia (CA). In many patients, candidate gene sequencing or focused resequencing arrays do not allow investigators to reach a genetic conclusion.
To assess the efficacy of exome-targeted capture sequencing to detect mutations in genes broadly linked to CA in a large cohort of undiagnosed patients and to investigate their prevalence.
DESIGN, SETTING, AND PARTICIPANTS: Three hundred nineteen index patients with CA and without a history of dominant transmission were included in the this cohort study by the Spastic Paraplegia and Ataxia Network. Centralized storage was in the DNA and cell bank of the Brain and Spine Institute, Salpetriere Hospital, Paris, France. Patients were classified into 6 clinical groups, with the largest being those with spastic ataxia (ie, CA with pyramidal signs [n = 100]). Sequencing was performed from January 1, 2014, through December 31, 2016. Detected variants were classified as very probably or definitely causative, possibly causative, or of unknown significance based on genetic evidence and genotype-phenotype considerations.
Identification of variants in genes broadly linked to CA, classified in pathogenicity groups.
The 319 included patients had equal sex distribution (160 female [50.2%] and 159 male patients [49.8%]; mean [SD] age at onset, 27.9 [18.6] years). The age at onset was younger than 25 years for 131 of 298 patients (44.0%) with complete clinical information. Consanguinity was present in 101 of 298 (33.9%). Very probable or definite diagnoses were achieved for 72 patients (22.6%), with an additional 19 (6.0%) harboring possibly pathogenic variants. The most frequently mutated genes were SPG7 (n = 14), SACS (n = 8), SETX (n = 7), SYNE1 (n = 6), and CACNA1A (n = 6). The highest diagnostic rate was obtained for patients with an autosomal recessive CA with oculomotor apraxia-like phenotype (6 of 17 [35.3%]) or spastic ataxia (35 of 100 [35.0%]) and patients with onset before 25 years of age (41 of 131 [31.3%]). Peculiar phenotypes were reported for patients carrying KCND3 or ERCC5 variants.
Exome capture followed by targeted analysis allows the molecular diagnosis in patients with highly heterogeneous mendelian disorders, such as CA, without prior assumption of the inheritance mode or causative gene. Being commonly available without specific design need, this procedure allows testing of a broader range of genes, consequently describing less classic phenotype-genotype correlations, and post hoc reanalysis of data as new genes are implicated in the disease.
在具有高度异质性遗传背景的疾病群体中，如小脑共济失调（CA），分子诊断难以实现。在许多患者中，候选基因测序或靶向重测序阵列无法让研究人员得出遗传结论。
评估外显子靶向捕获测序在一大群未确诊患者中广泛检测与 CA 相关基因的突变的效果，并研究其患病率。
设计、设置和参与者：该队列研究由 Spastic Paraplegia and Ataxia Network 纳入了 319 名小脑共济失调且无显性遗传史的索引患者。集中存储在法国巴黎 Salpetriere 医院脑与脊柱研究所的 DNA 和细胞库中。患者被分为 6 个临床组，最大的组是痉挛性共济失调（即有锥体束征的 CA [n=100]）。测序于 2014 年 1 月 1 日至 2016 年 12 月 31 日进行。根据遗传证据和基因型-表型考虑，将检测到的变体分类为极可能或肯定的致病、可能的致病或意义不明。
鉴定与 CA 广泛相关的基因中的变异，根据致病性进行分类。
319 名纳入患者的性别分布均衡（160 名女性[50.2%]和 159 名男性患者[49.8%]；平均[标准差]发病年龄为 27.9[18.6]岁）。298 名有完整临床信息的患者中，131 名（44.0%）发病年龄小于 25 岁。298 名患者中有 101 名（33.9%）存在近亲结婚。72 名患者（22.6%）获得了极可能或明确的诊断，另外 19 名（6.0%）携带可能的致病变异。最常突变的基因是 SPG7（n=14）、SACS（n=8）、SETX（n=7）、SYNE1（n=6）和 CACNA1A（n=6）。诊断率最高的是有眼球运动性运动不能样表型（17 名患者中的 6 名 [35.3%]）或痉挛性共济失调（100 名患者中的 35 名 [35.0%]）的常染色体隐性 CA 患者，以及发病年龄小于 25 岁的患者（131 名患者中的 41 名 [31.3%]）。携带 KCND3 或 ERCC5 变异的患者出现了特殊表型。
外显子捕获后靶向分析可实现高度异质性孟德尔疾病（如 CA）的分子诊断，无需预先假设遗传模式或致病基因。由于不需要特定的设计，该程序可以测试更广泛的基因，从而描述不太典型的表型-基因型相关性，并在新基因涉及疾病时进行事后数据分析。
