Recurrence and variability of germline EPCAM deletions in Lynch syndrome

Abstract

Recently, we identified 3' end deletions in the EPCAM gene as a novel cause of Lynch syndrome. These truncating EPCAM deletions cause allele-specific epigenetic silencing of the neighboring DNA mismatch repair gene MSH2 in tissues expressing EPCAM. Here we screened a cohort of unexplained Lynch-like families for the presence of EPCAM deletions. We identified 27 novel independent MSH2-deficient families from multiple geographical origins with varying deletions all encompassing the 3' end of EPCAM, but leaving the MSH2 gene intact. Within The Netherlands and Germany, EPCAM deletions appeared to represent at least 2.8% and 1.1% of the confirmed Lynch syndrome families, respectively. MSH2 promoter methylation was observed in epithelial tissues of all deletion carriers tested, thus confirming silencing of MSH2 as the causative defect. In a total of 45 families, 19 different deletions were found, all including the last two exons and the transcription termination signal of EPCAM. All deletions appeared to originate from Alu-repeat mediated recombination events. In 17 cases regions of microhomology around the breakpoints were found, suggesting nonallelic homologous recombination as the most likely mechanism. We conclude that 3' end EPCAM deletions are a recurrent cause of Lynch syndrome, which should be implemented in routine Lynch syndrome diagnostics.

The current value of determining the mismatch repair status of colorectal cancer: A rationale for routine testing

“…Germ line hemiallelic methylations of MLH1 or MSH2, termed "epimutations", have also been recognized as causative of Lynch syndrome Ollila et al, 2006;Sheng et al, 2006). Recently, deletions of the epithelial cell adhesion molecule (EpCAM) gene (previously known as TACSTD1, tumor-associated calcium signal transducer 1), which is located upstream of MSH2, have been implicated in Lynch syndrome (Kovacs et al, 2009;Kuiper et al, 2011;Ligtenberg et al, 2009). Deletions affecting the 3 exons of the EpCAM gene lead to a transcriptional read-through and mediate epigenetic silencing of the MSH2.…”

“…Deletions affecting the 3 exons of the EpCAM gene lead to a transcriptional read-through and mediate epigenetic silencing of the MSH2. Therefore, CRCs in individuals with heterozygous constitutional EpCAM deletions will be MSH2-negative MSI cancers (Kovacs et al, 2009;Kuiper et al, 2011;Ligtenberg et al, 2009). It is important to remember that a defect in MMR is not manifest until both alleles of an MMR gene are inactivated (Geiersbach and Samowitz, 2011).…”

“…It is also important to remember that in the subset of Lynch syndrome due to deletion of EpCAM somatic hypermethylation of MSH2 leads to loss of expression by IHC. However, genetic analysis for an MSH2 mutation is negative as the causative mutation is a deletion affecting the 3 exons of the EpCAM gene upstream of MSH2 and not in the MSH2 gene itself (Kovacs et al, 2009;Kuiper et al, 2011;Ligtenberg et al, 2009). A recent study showed that a lack of EpCAM immunostaining in MSH2-negative CRCs is indicative of EpCAM gene alterations with 100% specificity (Musulen et al, 2013).…”

Economic evaluation of genetic screening for Lynch syndrome in Germany

“…Also, we did not model CRC risk associated with the EPCAM gene, another gene that has recently been found to impact LS. 34 We did assume that mutation carriers adhering to regular colonoscopy also adhere to aspirin prevention. This might have biased our results for or against screening.…”

MLH1 methylation screening is effective in identifying epimutation carriers

“…MLH1 or MSH2 are the most commonly mutated MMR genes in LS, whereas mutations in MSH6 or PMS2 are significantly less common. 3,4 Occasionally, the presence of constitutional epimutations in MSH2 and MLH1 has been reported (reviewed in Hitchins and Ward 5 and Kuiper et al 6 ).…”