齿状核红核苍白球路易体萎缩一例：临床表型与基因突变分析

Clinical and genetic study of one DRPLA case

目的报告1例齿状核红核苍白球路易体萎缩(DRPLA)患者的临床特征和基因突变特点。方法采用聚合酶链反应对388例脊髓小脑共济失调患者(234例常染色体显性遗传家系先证者和1 54例散发病例)进行初步筛查,对琼脂糖凝胶电泳中出现2条电泳条带的样品应用荧光标记毛细管电泳基因片段分析方法进行脊髓小脑共济失调致病基因三核苷酸(CAG)重复序列突变检测并精确计数,最后经pUC18-T载体克隆测序验证重复次数达异常范围的样本。结果仅发现1例表现为轻度脊髓小脑共济失调和可疑癫癎发作的女性患者具有DRPLA基因CAG重复扩展突变。基因片段分析2个等位基因的CAG重复次数分别为14和54次,克隆测序重复次数为15和58次。其家系另2例成员均有癫癎发作史,但无明显共济失调表现。19例无异常扩展样本基因片段分析显示CAG重复次数为7～20次,其中9次重复最为常见。结论 DRPLA可能存在临床变异。388例脊髓小脑共济失调患者中仅发现1例DRPLA,说明该病在中国共济失调患者中相对罕见。在重复突变检测过程中,由于高度重复序列可产生局部二级结构,在复制过程中可能会出现DNA聚合酶的滑动,从而导致扩增产物的不忠实,这一问题在基因片段分析和克隆测序中均存在,且后者在操作过程中还可能出现克隆过程的不稳定,因此基于这两种方法的结果需要相互验证。

Objective To investigate the clinical and genetic features of dentatorubralpallidoluysian atrophy （DRPLA）. Methods The trinucleotide repeats of spinocerebellar ataxia （SCA） disease genes were detected by polymerase chain reaction （PCR） initially in 388 SCA cases which included 234 cases with autosomal dominant inheritance and 154 sporadic cases. Fragment analysis with laser- induced fluorescence in capillary electrophoresis was performed for the samples with 2 bands detected by agarose gel electrophoresis （AGE）. The repeat numbers of the positive or suspicious samples were verified by the pUCI8-T vector cloning and sequencing. Results Based on the 2 methods, the cytosine-adenine- guanine （CAG） repeat expansion of DRPLA gene was detected in one female ease with mild ataxia and suspected seizure. The repeat numbers of the 2 alleles were 14 and 54 by fragment analysis, and 15 and 58 by cloning sequencing. The 2 members of her family had a history of seizure, but no obvious ataxia. The CAG repeat numbers of the other 19 cases without abnormal expansions ranged from 7 to 20, of which 9 was common. Conclusion The patient＇s atypical manifestations suggests that clinical variation may exist in DRPLA. Only one case of DRPLA is found in 388 SCA cases, indicating that DRPLA may be a relatively rare subtype of SCA in Chinese population. The secondary structure of DNA owing to the highly repetitive sequences will induce DNA polymerase sliding during the amplification, which will reduce the fidelity in DNA replication. This problem exists in both fragment analysis and cloning sequencing. For the latter method, the instability also appears in the process of cloning. Therefore, the repeat numbers need to be mutually verified by the 2 methods.