WRN helicase is recently identified as an intriguing synthetic lethal target in dMMR or microsatellite instability high (MSI-H) cancers.336–338 In dMMR/MSI-H cancer cells featured by (TA)n-dinucleotide repeat expansions, WRN could unwind non-B DNA cruciform-like structures formed by (TA)n repeats during replication. The gene discussed is WRN; the disease is cancer.