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Biallelic germline nonsense variant of MLH3 underlies polyposis predisposition.
Genetics in Medicine ( IF 6.6 ) Pub Date : 2018-12-21 , DOI: 10.1038/s41436-018-0405-x
Alisa Olkinuora 1 , Taina T Nieminen 1, 2 , Emma Mårtensson 3, 4 , Anna Rohlin 4, 5 , Ari Ristimäki 6, 7 , Laura Koskenvuo 8 , Anna Lepistö 8 , , Samuel Gebre-Medhin 9, 10 , Margareta Nordling 4, 5 , Päivi Peltomäki 1
Affiliation  

PURPOSE Some 10% of familial adenomatous polyposis (FAP) and 80% of attenuated polyposis (AFAP) cases remain molecularly unexplained. We scrutinized such cases by exome-wide and targeted methods to search for novel susceptibility genes. METHODS Exome sequencing was conducted on 40 unexplained (mainly sporadic) cases with FAP or AFAP from Finland. The DNA mismatch repair (MMR) gene MLH3 (MutL Homolog 3) was pinpointed and prompted a subsequent screen of ~1000 Swedish patients referred to clinical panel sequencing for colon tumor susceptibility. RESULTS Three homozygous carriers of a truncating variant in MLH3, c.3563C>G, p.Ser1188Ter, were identified among the index cases from the Finnish series. An additional biallelic carrier of the same variant was present in the Swedish series. All four patients shared a 0.8-Mb core haplotype around MLH3, suggesting a founder variant. Colorectal polyps from variant carriers showed no instability at mono-, di-, tri-, or tetranucleotide repeats, in agreement with previous findings of a minor role of MLH3 in MMR. Multiple loci were affected by loss of heterozygosity, suggesting chromosomal instability. CONCLUSION Our results show that a biallelic nonsense variant of MLH3 underlies a novel syndrome with susceptibility to classical or attenuated adenomatous polyposis and possibly extracolonic tumors, including breast cancer.

中文翻译:

MLH3 的双等位基因种系无义变体是息肉易感性的基础。

目的 约 10% 的家族性腺瘤性息肉病 (FAP) 和 80% 的减毒息肉病 (AFAP) 病例在分子学上仍无法解释。我们通过外显子组和靶向方法仔细检查了这些病例,以寻找新的易感基因。方法 对来自芬兰的 40 例不明原因(主要是散发的)FAP 或 AFAP 病例进行外显子组测序。DNA 错配修复 (MMR) 基因 MLH3 (MutL Homolog 3) 被精确定位,并促使随后对约 1000 名瑞典患者进行筛查,这些患者参考了结肠肿瘤易感性的临床小组测序。结果在芬兰系列的索引病例中鉴定出三个 MLH3 截断变体的纯合子携带者,c.3563C>G,p.Ser1188Ter。瑞典系列中存在另一个相同变体的双等位基因载体。所有四名患者在 MLH3 周围共享一个 0.8 Mb 的核心单倍型,建议创建者变体。来自变异携带者的结直肠息肉在单核苷酸、双核苷酸、三核苷酸或四核苷酸重复序列中没有表现出不稳定性,这与先前发现的 MLH3 在 MMR 中的次要作用一致。多个基因座受到杂合性丧失的影响,表明染色体不稳定。结论 我们的研究结果表明,MLH3 的双等位基因无义变体是一种新综合征的基础,该综合征对经典或减毒的腺瘤性息肉病和可能的结肠外肿瘤(包括乳腺癌)易感。
更新日期:2019-01-26
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