Supplementary Material for: Whole exome sequencing indicating GGCCTG hexanucleotide repeat in patients with spinocerebellar ataxia type 36

Introduction: Spinocerebellar ataxia type 36 (SCA36) is caused by large GGCCTG repeat expansion in the NOP56 gene. The genetic diagnosis based on Southern blot is expensive and time-consuming. This study aimed to evaluate the reliability and effectiveness of whole exome sequencing (WES) for routine genetic diagnosis of suspected SCA36 patients.
Methods: Pathogenic repeat expansions for SCAs including SCA36 were first analyzed based on WES data using ExpansionHunter in five probands from SCA families, then the results were confirmed by triplet repeat primed polymerase chain reaction (TP-PCR) and Southern blot.
Results: GGCCTG repeat expansion in NOP56 was indicated in all five probands by WES, then it was found in 11 SCA patients and three asymptomatic individuals by TP-PCR. The sizes of GGCCTG repeat expansions were confirmed to be 1390-1556 by Southern blot. The mean age at onset of the patients was 51.0 ± 9.3 (ranging from 41 to 71), and they presented slowly progressive cerebellar ataxia, atrophy and fasciculation in tongue or limb muscles.
Conclusion: The patients were clinically and genetically diagnosed as SCA36. This study proposed that WES could be a rapid, reliable, and cost-effective routine test for the preliminarily detection of SCA36 and other ataxia diseases.

引言：36型脊髓小脑共济失调（Spinocerebellar ataxia type 36, SCA36）由NOP56基因中大片段GGCCTG重复扩增所致。基于Southern印迹法（Southern blot）的基因诊断成本高昂且耗时耗力。本研究旨在评估全外显子组测序（whole exome sequencing, WES）用于疑似SCA36患者常规基因诊断的可靠性与有效性。

方法：本研究首先针对5个来自脊髓小脑共济失调（SCA）家系的先证者，基于全外显子组测序数据，利用ExpansionHunter工具分析包括SCA36在内的各类SCA致病性重复扩增情况；随后通过三核苷酸重复引物聚合酶链反应（triplet repeat primed polymerase chain reaction, TP-PCR）与Southern印迹法对结果进行验证。

结果：全外显子组测序在全部5例先证者中均检出NOP56基因的GGCCTG重复扩增；后续通过三核苷酸重复引物聚合酶链反应在11例SCA患者与3例无症状个体中检出该扩增。Southern印迹法证实GGCCTG重复扩增的片段长度为1390~1556。患者的平均发病年龄为51.0±9.3岁（范围41~71岁），临床表现为缓慢进展的小脑共济失调、肌肉萎缩以及舌肌或肢体肌束震颤。

结论：本研究通过临床与基因学手段确诊患者为SCA36。本研究提出，全外显子组测序可作为一种快速、可靠且具有成本效益的常规检测手段，用于SCA36及其他共济失调类疾病的初步筛查。