Background & Aims

Although there is a genetic predisposition to colorectal cancer (CRC), few of the genes that affect risk have been identified. We performed whole-exome sequence analysis of individuals in a high-risk family without mutations in genes previously associated with CRC risk to identify variants associated with inherited CRC.

Methods

We collected blood samples from 3 relatives with CRC in Spain (65, 62, and 40 years old at diagnosis) and performed whole-exome sequence analyses. Rare missense, truncating or splice-site variants shared by the 3 relatives were selected. We used targeted pooled DNA amplification followed by next generation sequencing to screen for mutations in candidate genes in 547 additional hereditary and/or early-onset CRC cases (502 additional families). We carried out protein-dependent yeast growth assays and transfection studies in the HT29 human CRC cell line to test the effects of the identified variants.

Results

A total of 42 unique or rare (population minor allele frequency below 1%) nonsynonymous genetic variants in 38 genes were shared by all 3 relatives. We selected the BRF1 gene, which encodes an RNA polymerase III transcription initiation factor subunit for further analysis, based on the predicted effect of the identified variant and previous association of BRF1 with cancer. Previously unreported or rare germline variants in BRF1 were identified in 11 of 503 CRC families, a significantly greater proportion than in the control population (34 of 4300). Seven of the identified variants (1 detected in 2 families) affected BRF1 mRNA splicing, protein stability, or expression and/or function.

Conclusions

In an analysis of families with a history of CRC, we associated germline mutations in BRF1 with predisposition to CRC. We associated deleterious BRF1 variants with 1.4% of familial CRC cases, in individuals without mutations in high-penetrance genes previously associated with CRC. Our findings add additional evidence to the link between defects in genes that regulate ribosome synthesis and risk of CRC.

中文翻译：

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BRF1，RNA聚合酶III转录复合体的亚基，BRF1中的种系突变与遗传性大肠癌之间的关联。

背景与目标

尽管大肠癌（CRC）有遗传易感性，但几乎没有发现影响风险的基因。我们对高危家庭中的个体进行了全外显子序列分析，而先前与CRC风险相关的基因没有突变，以鉴定与遗传性CRC相关的变体。

方法

我们从西班牙的3名患有CRC的亲戚（诊断时分别为65、62和40岁）收集了血样，并进行了全外显子组序列分析。选择了由3个亲戚共享的稀有错义，截短或剪接位点的变异体。我们使用有针对性的合并DNA扩增，然后进行下一代测序，以筛选547个其他遗传和/或早发CRC病例（另外502个家庭）中候选基因的突变。我们在HT29人CRC细胞系中进行了蛋白质依赖性酵母生长测定和转染研究，以测试鉴定出的变体的作用。

结果

所有3个亲戚共有38个基因中的42个独特或稀有（种群次要等位基因频率低于1％）非同义遗传变异。我们基于鉴定出的变体的预测效果以及BRF1与癌症的先前关联，选择了BRF1基因，该基因编码RNA聚合酶III转录起始因子亚基用于进一步分析。在503个CRC家族中，有11个发现了BRF1以前未报道或罕见的种系变异，这一比例明显高于对照组（4300个中的34个）。已鉴定的变体中有7个（在2个家族中检测到1个）影响了BRF1 mRNA的剪接，蛋白质稳定性或表达和/或功能。

结论

在对有CRC病史的家庭进行的分析中，我们将BRF1的种系突变与CRC易感性相关联。我们将有害的BRF1变异与1.4％的家族性CRC病例相关联，这些个体以前没有与CRC相关的高渗透性基因突变。我们的发现为调节核糖体合成的基因缺陷与CRC风险之间的联系提供了更多证据。