The majority of known pathogenic NBN variants lead to protein truncation, resulting in partially functional protein (e.g., p70 or p45).21,43 These hypomorphic variants retain some activity in DNA damage response, and variability in their expression level seems to be linked to the degree of genome instability and cancer risk.34 This observation is supported by our finding that NBN protein stability and MMC drug sensitivity are strongly correlated. This evidence concerns the gene NBN and cancer.