Intergeneration CAG expansion in a Wuhan juvenile-onset Huntington disease family

Abstract

Objective

To make early diagnosis of IT15 gene mutation in a Wuhan juvenile-onset Huntington disease (HD) family, for providing them with genetic counseling, and making preparation for the further research on pathogenesis and experimental therapy of HD.

Methods

According to the principle of informed consent, we extracted genomic DNA from peripheral blood samples and carried genetic diagnosis of pathogenic exon 1 of IT15 gene by modified touchdown PCR and DNA sequencing methods.

Results

Eight of twenty-five family members carried abnormal allele: III₁₀, III₁₂, III₁₄, IV₃, and V₂ carried (CAG)₄₈, IV₁₁ and IV₁₂ carried (CAG)₆₇, and IV₁₄ carried (CAG)₆₃, in contrast with the 8–25 CAG trinucleotides in the members of control group. IV₁₄ carried 15 more CAG trinucleotides than her father III₁₀.

Conclusion

The results definitely confirm the diagnosis of HD and indicate the CAG trinucleotide repeat expansion of IT15 gene in this HD family. In addition, CAG expansion results in juvenile-onset and anticipation (characterized by earlier age of onset and increasing severity) of the patient IV₁₂.

摘要

目的

对青少年发病的亨廷顿舞蹈病(Huntington disease)家系进行致病 IT15 基因早期诊断分析, 为家系成员提供遗传咨询, 并为后续的HD发病机制及实验治疗研究提供依据。

方法

按照知情同意原则抽取家系成员外周血, 提取基因组DNA, 采用改良的降落 PCR 方法扩增 IT15 基因致病区域, DNA 测序检测异常等位基因 (CAG)_n 三核苷酸重复次数。

结果

在该家系三代 25 名成员中, 共发现 8 名致病 IT15 基因携带者, 其中, III₁₀、 III₁₂、 III₁₄、 IV₃ 和 V₂ CAG 三核苷酸的拷贝数均为 48, IV₁₁ 和 IV₁₂ 均为 (CAG)₆₇, IV₁₄ 为 (CAG)₆₃, 而对照组 35 名正常人的CAG三核苷酸的拷贝数为 8–25, 两者之间没有重叠。

结论

家系中第四代致病基因携带者 IV₁₄ 与第三代患者 III₁₀ 比较, CAG 三核苷酸重复次数增加 15 次, 即本家系 IT15 基因在传递过程中发生了扩增突变。同时扩增突变导致该家系出现青少年发病及遗传早现现象。