Nijmegen Breakage Syndrome (NBS) is an autosomal-recessive condition, caused by a biallelic loss-of-function (LOF) mutation in the NBN gene.8 About 90% of NBS patients are homozygous for the frameshift mutation, p.K219fs (c.657_661delACAAA), which is noted to be a founder mutation in populations of Eastern European (Slavic) descent.11,12 The NBN protein functions as a sensor for DNA double-strand breaks and an adaptor for the downstream repair signaling.11 The N-terminus contains a Forkhead-Associated and two Breast Cancer C-terminus domains (FHA-BCRT-repeat domain). The gene discussed is NBN; the disease is breast carcinoma.