Mutation analysis of the MLH1, MSH2 and MSH6 genes in patients with double primary cancers of the colorectum and the endometrium: A population‐based study in northern Sweden

Abstract

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder that predisposes to predominantly colorectal and endometrial cancers due to germline mutations in DNA mismatch repair genes, mainly MLH1, MSH2 and in families with excess endometrial cancer also MSH6. In this population-based study, we analysed the mutation spectrum of the MLH1, MSH2 and MSH6 genes in a cohort of patients with microsatellite unstable double primary tumours of the colorectum and the endometrium by PCR, DHPLC and sequencing. nl).A germline mutation in one of the MMR genes in HNPCC patients predisposes to an early onset colon cancer: 30% risk to age 40 and over 80% lifetime risk, 9 compared to 3-4% in the general population. In addition, affected individuals are prone to develop multiple primary cancers, both from the colorectum and extracolonic sites, of which endometrial cancers are the most common with a lifetime risk of 20 -43% in women, 10 followed by carcinoma of the ovary, stomach, small intestine and upper urinary tract. 11 When the MMR system is defective, especially when due to MLH1 and MSH2 mutations, replication errors arising during DNA replication are not corrected, which results in widespread genomic instability. Through their repetitive nature, microsatellites are particularly prone to replication errors and therefore microsatellite instability (MSI) is a hallmark of MMR deficiency. MSI is found in more than 90% of all HNPCC tumours 12 but only in 10 -15% of sporadic colorectal tumours. 13 Moreover, MMR deficiency leads to an increased mutation rate in specific cancer related genes, including BAX, 14 IGFIIR 15 and TGF-␤ type II receptor, 16 which may enhance tumour progression. While MLH1 and MSH2 defects give instability primarily in dinucleotide repeats, 13 MSH6-defective tumours show alterations in predominantly mononucleotide repeats. [17][18][19] This is in congruence with the biological function, where MLH1 and MSH2 manage repair of small insertion/deletion loops, 20,21 while MSH6 mostly is involved in repair of base-base and single nucleotide insertion/deletion mismatches. 22,23 Double primary cancers within the HNPCC spectrum is a hallmark of HNPCC and an indicator to clinically suspect HNPCC. 24 In a previous population-based study, 25 we observed an increased risk of HNPCC-associated cancers in first-degree relatives to patients diagnosed with double primary cancers of the colorectum or the colorectum/endometrium. The overall standardised incidence ratio (SIR) was 1.69 (95% CI; 1.39 -2.03). The SIR was highest among relatives to the patients with young age of onset (Ͻ50 years) and MSI positive tumours. The aim of our study was to investigate the MLH1, MSH2 and MSH6 mutation spectrum in the patients with MSI positive double primary tumours. MATERIAL AND METHODS PatientsSeventy-eight patients with double primary cancers of the colorectum or the colorectum and the endometrium (Fig. 1) were identified in a population-based cohort study previously reported. 25 The MSI status of one of the patie...

Uncertain pathogenicity of MSH2 variants N127S and G322D challenges their classification

“…Indeed, Tanyi et al reported an HNPCC family with a truncating mutation in MSH2, which when in combination with MSH2 N127S leads to HNPCC phenotype in very early age. 17 Although the majority of the published data discusses MSH2 G322D as a neutral polymorphism, 3,5,[7][8][9][10][11][12] it has also been hypothesized to be a low penetrance allele. 24 This interpretation was supported by the functional analyses conducted with yeast assays, where the putative homologous mutation Msh2 D317D in yeast was reported to cause a moderate, as yet not complete inactivation of MMR.…”

“…It was suggested to be polymorphic when it was not segregating with the cancer phenotype in a family or it was found in healthy control individuals. 3,5,[7][8][9][10][11][12] Contrary to these, it was interpreted as a low penetrance allele based on moderate inactivation of yeast MMR caused by a homologous yeast variant. 13,14 It was also interpreted as pathogenic when it was segregating with the cancer phenotype, and showed loss of MSH2 protein and high microsatellite instability (MSI) in the tumor, 15 or when it was not found in healthy control chromosomes.…”

hMLH1 promoter methylation and silencing in primary endometrial cancers are associated with specific alterations in MBDs occupancy and histone modifications

“…Endometrial cancers occur with increased rates in women with hereditary nonpolyposis colorectal cancer (HNPCC), an autosomal dominant disorder that is linked to germ line mutations in one or more of the mismatch repair (MMR) genes including MLH1, MSH2 and MSH6 [1]. A direct consequence of DNA repair deficiency is the accumulation of DNA replication errors, or mutator phenotype, represented by high frequency of microsatellite instability (MSI-H).…”

Transcriptional profiling endometrial carcinomas microdissected from DES‐treated mice identifies changes in gene expression associated with estrogenic tumor promotion

“…Molecular and epidemiological studies have highlighted key genetic factors in human endometrial tumorigenesis, including loss or epigenetic silencing of the tumor suppressor gene phosphatase and tensin homologue (PTEN) 1 and the DNA mismatch repair (MMR) genes mutL homologue 1 (MLH1), mutS homologue 2 (MSH2) and mutS homologue 6 (MSH6). [2][3][4][5] It is widely accepted that exposure to unopposed estrogen (estrogen in the absence of progesterone) is a potent environmental risk factor for the development of a variety of malignancies, and in particular endometrial carcinoma. [6][7][8] However, deciphering the genes and pathways that are disturbed in estrogen-promoted endometrial cancers has been a difficult task, due in part to the inherent genetic and hormonal heterogeneity that characterizes this tumor type.…”