In 20–30% of patients suspected of a familial colorectal cancer (CRC) syndrome, no underlying genetic cause is detected. Recent advances in whole exome sequencing have generated evidence for new CRC-susceptibility genes including POLE, POLD1 and NTHL1¸ but many patients remain unexplained. Whole exome sequencing was performed on DNA from nine patients from five different families with familial clusters of CRC in which traditional genetic testing failed to yield a diagnosis. Variants were filtered by minor allele frequencies, followed by prioritization based on in silico prediction tools, and the presence in cancer susceptibility genes or genes in cancer-associated pathways. Effects of frameshift variants on protein structure were modeled using I-Tasser. One known pathogenic variant in POLD1 was detected (p.S478N), together with variants in 17 candidate genes not previously associated with CRC. Additional in silico analysis using SIFT, PROVEAN and PolyPhen on the 14 missense variants indicated a possible damaging effect in nine of 14 variants. Modeling of the insertions/deletions showed a damaging effect of two variants in NOTCH2 and CYP1B1. One family was explained by a mutation in a known familial CRC gene. In the remaining four families, the most promising candidates found are a frameshift NOTCH2 and a missense RAB25 variant. This study provides potential novel candidate variants in unexplained familial CRC patients, however, functional validation is imperative to confirm the role of these variants in CRC tumorigenesis. Additionally, while whole exome sequencing enables detection of variants throughout the exome, other causes explaining the familial phenotype such as multiple single nucleotide polymorphisms accumulating to a polygenic risk or epigenetic events, might be missed with this approach.

中文翻译：

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新型的早期家族性结直肠癌候选药物。

在20-30％的怀疑患有家族性结直肠癌（CRC）综合征的患者中，未发现潜在的遗传原因。全外显子组测序的最新进展为新的CRC易感基因（包括POLE，POLD1和NTHL1）提供了证据但许多患者仍无法解释。对来自五个不同家族的CRC家族簇的9例患者的DNA进行了完整的外显子组测序，传统的基因检测未能得出诊断结果。通过较小的等位基因频率过滤变异体，然后基于计算机模拟预测工具确定优先级，并在癌症易感基因或与癌症相关的通路中存在基因。使用I-Tasser对移码变体对蛋白质结构的影响进行建模。POLD1中的一种已知致病变体检测到了p.S478N（p.S478N），以及先前未与CRC相关的17个候选基因的变体。使用SIFT，PROVEAN和PolyPhen对14个错义变体进行的其他计算机分析表明，在14个变体中的9个中可能有破坏作用。插入/缺失的建模显示NOTCH2和CYP1B1中两个变体的破坏作用。一个家族由已知家族性CRC基因的突变解释。在其余四个家庭中，发现的最有前途的候选对象是移码NOTCH2和错义的RAB25变体。这项研究为无法解释的家族性CRC患者提供了潜在的新型候选变异体，但是，必须进行功能验证以确认这些变异体在CRC肿瘤发生中的作用。此外，虽然整个外显子组测序可以检测整个外显子组中的变异，但使用这种方法可能会遗漏解释家族表型的其他原因，例如积累到多基因风险或表观遗传事件的多个单核苷酸多态性。