MRC1 and Marinesco-Sjogren syndrome: Although several studies have shown that WRN is a SL target of MSI cancer cells, restoration of MMR functions through ectopic expression of MMR-associated genes in MSI cell lines only showed partial rescue of cell viability [60] upon WRN KO, and generating MSI conditions through MMR gene KOs in MSS cell lines failed to recapitulate the lethal effects of WRN KO [122].