一例TSC2基因低比例突变嵌合体基因学分析

目的: 对一例临床表现不典型的结节性硬化症（TSC）患者进行基因突变分析以明确诊断。方法: 收集一例临床上拟诊TSC的患者及其父母的外周血，通过全外显子组测序技术对先证者TSC1和TSC2基因的全部外显子及其侧翼序列进行测序，确定候选致病突变位点，同时对先证者及其父母的外周血DNA进行Sanger测序验证，并用液滴数字PCR技术确定先证者体细胞中该突变嵌合比例。结果: 先证者的TSC2基因第11号外显子存在c.1096G>T（p.E366*）杂合无义突变，为微小突变峰，突变比例未高于其突变阈值，不排除嵌合体的可能。液滴数字PCR结果提示，先证者为c.1096G>T点突变嵌合体，嵌合比例为14%。结论: 先证者TSC2基因发生体细胞镶嵌突变，c.1096G>T可能是该TSC患者的致病原因。液滴数字PCR有助于体细胞镶嵌突变嵌合体的确诊。

Genetic analysis of a mosaic case with low proportion mutation of TSC2 gene

Objective: To perform gene mutation analysis in a patient with atypical clinical manifestations of tuberous sclerosis (TSC) for definite diagnosis. Methods: Peripheral blood DNA was obtained from a patient with clinically suspected TSC and her parents, and all exons and their flanking sequences of TSC1 and TSC2 genes in the proband were sequenced by whole exome sequencing to determine the candidate pathogenic mutations. At the same time, Sanger sequencing was performed to verify the peripheral blood DNA of the patient and her parents. And the mosaic percentage of the mutation in the proband's somatic cells was detected by the droplet digital PCR method. Results: A heterozygous nonsense mutation c.1096G>T (p.E366*) was identified in the exon 11 of the TSC2 gene, which only had a small mutation peak. A lower percentage of the mutation was found in the DNA of the patient than that in the public database, therefore the possibility of mosaicism might not be excluded. In addition, the droplet digital PCR method demonstrated that the proband was a c.1096G>T mutant mosaicism, and the mosaic percentage was 14%. Conclusions: The somatic mosaic mutation c.1096G>T (p.e366*) may be responsible for the phenotype of TSC in this patient. And the drop digital PCR is expected to be a diagnostic method for somatic cells mosaicism.