Department of Health and Environmental Sciences, Graduate School of Medicine, Kyoto University, Japan.
Am J Hum Genet. 2011 Jul 15;89(1):121-30. doi: 10.1016/j.ajhg.2011.05.015. Epub 2011 Jun 16.
Autosomal-dominant spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative disorders. In this study, we performed genetic analysis of a unique form of SCA (SCA36) that is accompanied by motor neuron involvement. Genome-wide linkage analysis and subsequent fine mapping for three unrelated Japanese families in a cohort of SCA cases, in whom molecular diagnosis had never been performed, mapped the disease locus to the region of a 1.8 Mb stretch (LOD score of 4.60) on 20p13 (D20S906-D20S193) harboring 37 genes with definitive open reading frames. We sequenced 33 of these and observed a large expansion of an intronic GGCCTG hexanucleotide repeat in NOP56 and an unregistered missense variant (Phe265Leu) in C20orf194, but we found no mutations in PDYN and TGM6. The expansion showed complete segregation with the SCA phenotype in family studies, whereas Phe265Leu in C20orf194 did not. Screening of the expansions in the SCA cohort cases revealed four additional occurrences, but none were revealed in the cohort of 27 Alzheimer disease cases, 154 amyotrophic lateral sclerosis cases, or 300 controls. In total, nine unrelated cases were found in 251 cohort SCA patients (3.6%). A founder haplotype was confirmed in these cases. RNA foci formation was detected in lymphoblastoid cells from affected subjects by fluorescence in situ hybridization. Double staining and gel-shift assay showed that (GGCCUG)n binds the RNA-binding protein SRSF2 but that (CUG)(6) does not. In addition, transcription of MIR1292, a neighboring miRNA, was significantly decreased in lymphoblastoid cells of SCA patients. Our finding suggests that SCA36 is caused by hexanucleotide repeat expansions through RNA gain of function.
常染色体显性遗传性小脑共济失调（SCA）是一组异质性的神经退行性疾病。在这项研究中，我们对一种独特形式的 SCA（SCA36）进行了遗传分析，这种 SCA 伴有运动神经元受累。对一组 SCA 病例中三个不相关的日本家族进行全基因组连锁分析和随后的精细定位，这些家族中的患者从未进行过分子诊断，将疾病基因座定位到 20p13 上一个 1.8Mb 延伸区域（20p13 上的 D20S906-D20S193，LOD 得分 4.60），该区域包含 37 个具有明确开放阅读框的基因。我们对其中的 33 个基因进行了测序，发现 NOP56 中的一个内含子 GGCCTG 六核苷酸重复序列发生了大量扩增，以及 C20orf194 中的一个未注册的错义变异（Phe265Leu），但在 PDYN 和 TGM6 中未发现突变。在家族研究中，扩增与 SCA 表型完全分离，而 C20orf194 中的 Phe265Leu 则没有。在 SCA 病例队列中对扩增进行筛查发现了另外四个病例，但在 27 例阿尔茨海默病病例、154 例肌萎缩侧索硬化症病例或 300 例对照病例中均未发现。总共在 251 例 SCA 患者队列中发现了 9 例（3.6%）不相关的病例。在这些病例中证实存在一个创始单倍型。通过荧光原位杂交，在受影响个体的淋巴母细胞系中检测到 RNA 焦点形成。双染色和凝胶迁移实验表明，（GGCCUG）n 结合 RNA 结合蛋白 SRSF2，但（CUG）（6）则不结合。此外，SCA 患者的淋巴母细胞中邻近 miRNA MIR1292 的转录显著降低。我们的发现表明，SCA36 是由六核苷酸重复扩增引起的 RNA 获得功能。
