Abstract: Objective To summarize the clinical, imaging and genetic characteristics of spinocerebellar ataxia 2 (SCA2) families presenting as Parkinsonism. Methods and Results Two families with autosomal dominant SCA2 with Parkinson's syndrome diagnosed by genetic test in Peking University First Hospital from May 2019 to December 2020 were included. The probands in 2 families manifested as lead-pipe like rigidity and cerebellum ataxia. Electronystagmography (ENG) in proband of family 1 showed gaze nystagmus, understable saccade, decreased smooth tracking ability and disappeared optokinetic nystagmus, proband of family 2 showed slow saccade, decreased smooth tracking ability and decreased optokinetic nystagmus. Head MRI in both probands of 2 families showed slightly enlarged third ventricle, while the proband of family 2 showed atrophy in brain stem and cerebellar. Whole exome sequencing (WES) in 2 probands showed no gene mutations, Sanger sequencing showed dynamic mutation of ATXN2 gene and the copy number of cytosine-adenine-guanine (CAG) with 37 repeats. Two probands were finally diagnosed as SCA2, and two pedigrees were diagnosed as SCA2 pedigrees. Conclusions SCA2 can present as Parkinsonism, which is easily to be misdiagnosed as Parkinson's disease due to the effective treatment of levodopa. ENG is helpful in detecting subclinical cerebellar lesions. For Parkinsonism patients with family history, especially when cerebellar lesions are involved, ATXN2 gene testing is recommended.

Key words: Spinocerebellar ataxias, Parkinsonian disorders, Genes, Mutation, Trinucleotide repeat expansion, Pedigree

摘要： 目的 总结表现为帕金森综合征的脊髓小脑性共济失调2型（SCA2）的临床、影像学和基因突变特点。方法与结果 纳入2019年5月至2020年12月在北京大学第一医院就诊的经基因检测诊断明确的表现为帕金森综合征的常染色体显性遗传性SCA2型两家系。两家系2例先证者均可见肌张力铅管样增高，症状与体征提示存在小脑性共济失调。眼震电图家系1先证者表现为凝视性眼震、扫视欠射、平稳跟踪能力下降和视动性眼震消失；家系2先证者表现为慢扫视、平稳跟踪能力下降和视动性眼震减少。头部MRI均显示第三脑室轻度扩张，家系2先证者还可见小脑和脑干萎缩。全外显子组测序未见帕金森病相关致病性变异； Sanger测序均显示ATXN2基因CAG序列重复次数为37次。2例先证者最终诊断为SCA2型，两家系诊断为SCA2型家系。结论 SCA2型可以表现为帕金森综合征，左旋多巴治疗有效，易误诊为帕金森病。眼震电图有助于发现亚临床小脑病变。对有阳性家族史的帕金森综合征患者，合并小脑病变时建议行ATXN2基因检测。

关键词: 脊髓小脑共济失调, 帕金森障碍, 基因, 突变, 三核苷酸重复扩增, 系谱