XRRA1 (X-ray radiation resistance associated 1) is a conserved nuclear and cytoplasmic protein encoded by an 11-exon gene on chromosome 11.3 that plays a critical role in cellular radiation response and DNA repair 1. The protein regulates X-ray sensitivity primarily through modulation of the ATM/CHK1/2 DNA damage response pathway; reduced XRRA1 expression increases phosphorylation of CHK1, CHK2, and ATM while decreasing γ-H2AX, thereby promoting DNA repair and radioresistance in colorectal cancer cells 2. XRRA1 also influences cell cycle progression by regulating cyclin A, cyclin E, and p21 expression, with reduced XRRA1 causing G2/M arrest 2. Beyond radiation response, XRRA1 variants associate with multiple disease phenotypes: a lung expression quantitative trait locus (11q13.4, rs7480008) was identified in asthma susceptibility in African American populations 3, and chromosome 11.4 associations linked XRRA1 to white blood cell count trajectories involving double-strand break DNA repair regulation 4. XRRA1 shows predominant testis expression and responds to environmental stressors; diesel exhaust particle exposure increased XRRA1 expression 2.3-fold in mouse testis 5. The gene exhibits widespread tumor cell expression and is proposed as a male prolactinoma biomarker 6, suggesting broader relevance in cancer development and therapy resistance.