Utilizing whole-exome sequencing, we could demonstrate that four out of five families with familial MPN presented with germline mutations in genes involved in DNA double-strand break (DSB) repair-associated genes (i.e., BRCA1, BRCA2, ATM, and CHEK2), suggesting that these germline mutations might increase the risk of acquiring a somatic MPN driver mutation [7]. The gene discussed is ATM; the disease is myeloproliferative neoplasm.