Telomere length and genetic anticipation in lynch syndrome

Telomere length variation has been associated with increased risk of several types of tumors, and telomere shortening, with genetic anticipation in a number of genetic diseases including hereditary cancer syndromes. No conclusive studies have been performed for Lynch syndrome, a hereditary colorectal cancer syndrome caused by germline mutations in the DNA mismatch repair genes. Here we evaluate telomere length in Lynch syndrome, both as a cancer risk factor and as a mechanism associated with anticipation in the age of cancer onset observed in successive generations of Lynch syndrome families. Leukocyte telomere length was measured in 244 mismatch repair gene mutation carriers from 96 Lynch syndrome families and in 234 controls using a monochrome multiplex quantitative PCR method. Cancer-affected mutation carriers showed significantly shorter telomeres than cancer-free mutation carriers. In addition, cancer-affected carriers showed the most pronounced shortening of telomere length with age, compared with unaffected carriers. The anticipation in the age of cancer onset observed in successive generations was not associated with telomere shortening, although, interestingly, all mother-son pairs showed telomere shortening. In conclusion, cancer-affected mismatch repair gene mutation carriers have distinct telomere-length pattern and dynamics. However, anticipation in the age of onset is not explained by telomere shortening. Pending further study, our findings suggest that telomere attrition might explain the previously reported dependence of cancer risk on the parent-of-origin of mismatch repair gene mutations

Estudi de variants de significat desconegut en la síndrome de Lynch

[cat] La síndrome de Lynch és la síndrome hereditària de predisposició al càncer colorectal més freqüent, i està causada per mutacions germinals en els gens reparadors MLH1, MSH2, MSH6 o PMS2. L'anàlisi mutacional dels gens reparadors és moltes vegades no informatiu, degut a la detecció de variants de significat desconegut (VSD). Aquestes variants representen fins a un 30% de les alteracions detectades i és especialment complicat predir el seu efecte funcional, ja que podran interferir en el correcte processament del mRNA o en la funció de la proteïna. La identificació de VSD suposa una limitació important per a la correcta avaluació del risc de predisposició al càncer. L'objectiu d'aquesta tesi és avaluar l'impacte funcional de les VSD detectades en els gens MLH1 i PMS2 en pacients amb sospita de síndrome de Lynch. Per això hem fet estudis a nivell de splicing del mRNA, d'expressió de mRNA i proteïna, així com assaigs funcionals de reparació i estudis de localització subcel•lular. Els resultats aquí recollits permeten classificar un 81,2% de totes les VSD analitzades, el 56% s'han classificat com patogèniques i el 25% com probablement neutrals. Cal destacar, que dues de les VSD analitzades i que es van detectar amb una elevada prevalença en la nostra població, han estat caracteritzades com les primeres mutacions fundadors en el gen MLH1 identificades a Espanya, presentant una penetrància moderada. També proposem un algoritme d'estudi de variants que permeti integrar i prioritzar les diferents tècniques fins a la caracterització funcional. La classificació d'aquestes VSD ens ha permès millorar l'assessorament genètic d'aquestes famílies, permetent l'estudi predictiu de familiars de risc, així com la personalització de mesures de prevenció i seguiment apropiats.[eng] Lynch syndrome (LS) is the most common hereditary colorectal cancer syndrome and is secondary to the presence of germline mutations in one of the DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2). Many mutations are short insertions, deletions, or nucleotide substitutions that will encode a truncated protein. These mutations are classified as pathogenic offering a good clinical tool for diagnosis and genetic counseling. However, clinical implications of missense or silent variants or mutations close to splice site are often not clear. Therefore, those variants are classified as variants of unknown significance (VUS) and represent up to 30% of the identified DNA changes in MMR genes. The scientific problem is to classify as either “pathogenic” or “not pathogenic” all MMR gene VUS identified by genetic testing for LS. The overarching goal of our studies was to assess the pathogenicity of MLH1 and PMS2 VUS detected in patients suspected to have LS. For their classification, we followed a strategy that integrates family history, pathology in tumors, and frequency in control/general population with an integrative approach including in silico and in vitro analyses at the RNA and protein level. This comprehensive analysis allowed classifying 81.2% of all VUS detected in the genes MLH1 and PMS2 in our series, this characterization has allowed classifying 56% of the variants analyzed as pathogenic and 25% as probably neutral. Furthermore, we have identified and characterized two frequent MLH1 variants among Spanish Lynch syndrome families. They represent the first founder MLH1 mutations identified in the Spanish population with moderate penetrance. Also, based on our observations we proposed an algorithm for the evaluation of VUS. We posit that this strategy provides a useful framework that emphasizes the importance of clinical information; suggest that in silico predictions can be of help in prioritizing RNA or protein assays in a mutually exclusive manner; and provides a useful framework for including all information when assessing a VUS. These findings have important implications for genetic counseling and molecular diagnosis of LS

Telomere length and genetic anticipation in lynch syndrome

Telomere length variation has been associated with increased risk of several types of tumors, and telomere shortening, with genetic anticipation in a number of genetic diseases including hereditary cancer syndromes. No conclusive studies have been performed for Lynch syndrome, a hereditary colorectal cancer syndrome caused by germline mutations in the DNA mismatch repair genes. Here we evaluate telomere length in Lynch syndrome, both as a cancer risk factor and as a mechanism associated with anticipation in the age of cancer onset observed in successive generations of Lynch syndrome families. Leukocyte telomere length was measured in 244 mismatch repair gene mutation carriers from 96 Lynch syndrome families and in 234 controls using a monochrome multiplex quantitative PCR method. Cancer-affected mutation carriers showed significantly shorter telomeres than cancer-free mutation carriers. In addition, cancer-affected carriers showed the most pronounced shortening of telomere length with age, compared with unaffected carriers. The anticipation in the age of cancer onset observed in successive generations was not associated with telomere shortening, although, interestingly, all mother-son pairs showed telomere shortening. In conclusion, cancer-affected mismatch repair gene mutation carriers have distinct telomere-length pattern and dynamics. However, anticipation in the age of onset is not explained by telomere shortening. Pending further study, our findings suggest that telomere attrition might explain the previously reported dependence of cancer risk on the parent-of-origin of mismatch repair gene mutations