背景:马凡综合征(MFS)是一种由原纤维蛋白-1基因(FBN1)突变引起的常染色体显性遗传多系统疾病。其中一小部分是拷贝数变异(CNVs),这可以通过基于重组的方式发生,基于复制的机制或逆向转位。在MFS中没有多少被精确地表征。
方法:一名疑似马凡氏综合征的女性患者在我们研究所接受基因检测。在对FBN1,TGFBR1和TGFBR2基因进行系统测序后,应用多重连接依赖性探针扩增。远程PCR,随后使用设计的引物进行Sanger测序,并应用初步的硅分析对断点进行了精确表征。
结果:初步分析显示,影响FBN1基因外显子46和47的从头大缺失,这导致第31和第32钙结合EGFlike结构域的丢失。对断点的进一步检查显示了位于内含子区域中的4916个核苷酸长的缺失。令人惊讶的是,在连接处检测到“TG”二核苷酸插入。我们假设CNV形成是由基于已知的微同源介导的断裂诱导复制(MMBIR)的罕见事件产生的。
结论:越来越多的CNV与孟德尔疾病和其他性状有关。MFS中大约2-7%的病例是由CNV引起的。到目前为止,几乎没有提出任何模型来证明FBN1基因中这些基因组重排的形成。特此,借助以前的模型和断点分析,我们提出了这种大缺失形成的潜在机制(基于MMBIR)。
Marfan syndrome (MFS) is an autosomal dominant multisystem disorder caused by mutations in the fibrillin-1 gene (FBN1). A small portion of them is copy number variations (CNVs), which can occur through recombination-based, replication-based mechanisms or retrotransposition. Not many have been characterized precisely in MFS.
A female patient with suspected Marfan syndrome was referred for genetic testing at our institute. After systematic sequencing of FBN1, TGFBR1, and TGFBR2 genes, multiplex ligation-dependent probe amplification was applied. Long-range PCR, subsequent Sanger sequencing with designed primers, and preliminary in silico analysis were applied for the precise characterization of the breakpoints.
Primary analysis displayed a de novo large deletion affecting exons 46 and 47 in the FBN1 gene, which resulted in the loss of the 31st and 32nd calcium-binding EGFlike domains. Further examination of the breakpoints showed a 4916 nucleotide long deletion localized in intronic regions. Surprisingly a \'TG\' dinucleotide insertion was detected at the junction. We hypothesize that the CNV formation was generated by a rare event based on the known microhomology-mediated break-induced replication (
MMBIR).
An increasing number of CNVs are associated with Mendelian diseases and other traits. Approximately 2-7% of the cases in MFS are caused by CNVs. Up to date, hardly any model was proposed to demonstrate the formation of these genomic rearrangements in the FBN1 gene. Hereby, with the help of previous models and breakpoint analysis, we presented a potential mechanism (based on
MMBIR) in the formation of this large deletion.