Rosty Christophe, Clendenning Mark, Walsh Michael D, Eriksen Stine V, Southey Melissa C, Winship Ingrid M, Macrae Finlay A, Boussioutas Alex, Poplawski Nicola K, Parry Susan, Arnold Julie, Young Joanne P, Casey Graham, Haile Robert W, Gallinger Steven, Le Marchand Loïc, Newcomb Polly A, Potter John D, DeRycke Melissa, Lindor Noralane M, Thibodeau Stephen N, Baron John A, Win Aung Ko, Hopper John L, Jenkins Mark A, Buchanan Daniel D
Envoi Pathology, Brisbane, Queensland, Australia The School of Medicine, The University of Queensland, Brisbane, Queensland, Australia Genetic Epidemiology Laboratory, Department of Pathology, The University of Melbourne, Parkville, Victoria, Australia.
Genetic Epidemiology Laboratory, Department of Pathology, The University of Melbourne, Parkville, Victoria, Australia.
BMJ Open. 2016 Feb 19;6(2):e010293. doi: 10.1136/bmjopen-2015-010293.
Immunohistochemistry for DNA mismatch repair proteins is used to screen for Lynch syndrome in individuals with colorectal carcinoma (CRC). Although solitary loss of PMS2 expression is indicative of carrying a germline mutation in PMS2, previous studies reported MLH1 mutation in some cases. We determined the prevalence of MLH1 germline mutations in a large cohort of individuals with a CRC demonstrating solitary loss of PMS2 expression.
This cohort study included 88 individuals affected with a PMS2-deficient CRC from the Colon Cancer Family Registry Cohort. Germline PMS2 mutation analysis (long-range PCR and multiplex ligation-dependent probe amplification) was followed by MLH1 mutation testing (Sanger sequencing and multiplex ligation-dependent probe amplification).
Of the 66 individuals with complete mutation screening, we identified a pathogenic PMS2 mutation in 49 (74%), a pathogenic MLH1 mutation in 8 (12%) and a MLH1 variant of uncertain clinical significance predicted to be damaging by in silico analysis in 3 (4%); 6 (9%) carried variants likely to have no clinical significance. Missense point mutations accounted for most alterations (83%; 9/11) in MLH1. The MLH1 c.113A> G p.Asn38Ser mutation was found in 2 related individuals. One individual who carried the MLH1 intronic mutation c.677+3A>G p.Gln197Argfs*8 leading to the skipping of exon 8, developed 2 tumours, both of which retained MLH1 expression.
A substantial proportion of CRCs with solitary loss of PMS2 expression are associated with a deleterious MLH1 germline mutation supporting the screening for MLH1 in individuals with tumours of this immunophenotype, when no PMS2 mutation has been identified.
DNA错配修复蛋白免疫组化用于筛查结直肠癌（CRC）患者的林奇综合征。虽然PMS2表达单独缺失表明携带PMS2种系突变，但既往研究报道部分病例存在MLH1突变。我们在一大群PMS2表达单独缺失的CRC患者中确定了MLH1种系突变的患病率。
这项队列研究纳入了来自结肠癌家族登记队列的88例PMS2缺陷型CRC患者。先进行种系PMS2突变分析（长程PCR和多重连接依赖探针扩增），随后进行MLH1突变检测（桑格测序和多重连接依赖探针扩增）。
在66例完成突变筛查的患者中，我们鉴定出49例（74%）存在致病性PMS2突变，8例（12%）存在致病性MLH1突变，3例（4%）存在通过计算机分析预测具有损害性的临床意义不确定的MLH1变异；6例（9%）携带可能无临床意义的变异。错义点突变占MLH1中大多数改变（占83%；9/11）。在2名相关个体中发现了MLH1 c.113A>G p.Asn38Ser突变。1名携带MLH1内含子突变c.677+3A>G p.Gln197Argfs*8导致外显子8跳跃的个体发生了2个肿瘤，这2个肿瘤均保留MLH1表达。
相当一部分PMS2表达单独缺失的CRC与有害的MLH1种系突变相关，这支持在未鉴定出PMS2突变的这种免疫表型肿瘤患者中筛查MLH1。
