A Novel Locus Predicts Spermatogenic Recovery among Childhood Cancer Survivors Exposed to Alkylating Agents

Exposure to high doses of alkylating agents is associated with increased risk of impaired spermatogenesis among nonirradiated male survivors of childhood cancer, but there is substantial variation in this risk. Here we conducted a genetic study for impaired spermatogenesis utilizing whole-genome sequencing data from 167 nonirradiated male childhood cancer survivors of European ancestry from the St. Jude Lifetime Cohort treated with cyclophosphamide equivalent dose (CED) ≥4,000 mg/m². Sperm concentration from semen analysis was assessed as the primary outcome. Common variants (MAF > 0.05) were adjusted for age at cancer diagnosis, CED, and top principal components. Rare/low-frequency variants (MAF ≤ 0.05) were evaluated jointly by various functional annotations and 4-kb sliding windows. A novel locus at 7q21.3 containing TAC1/ASNS was associated with decreased sperm concentration (rs7784118: P = 3.5 × 10^-8). This association was replicated in two independent samples of SJLIFE survivors of European ancestry, including 34 nonirradiated male survivors treated with 0 < CED < 4,000 mg/m² (P = 3.1 × 10^-4) and 24 male survivors treated with CED ≥4,000 mg/m² and radiotherapy <40 Gray (P = 0.012). No association was observed among survivors not exposed to alkylating agents included in the CED (P > 0.29). rs7784118 conferred 3.48- and 9.73-fold increases in risk for clinically defined oligospermia and azoospermia and improved prediction of normospermic, oligospermic, and azoospermic states by 13.7%, 5.3%, and 21.7%. rs7784118 was associated with decreased testosterone level, increased levels of follicle stimulating and luteinizing hormones, and 8.52-fold increased risk of Leydig cell failure. Additional research is warranted to determine how this SNP influences spermatogenesis and to assess its clinical utility in characterizing high-risk survivors and guiding intervention strategies. SIGNIFICANCE: The identified genetic markers harbor potential clinical utility in characterizing high-risk survivors and guiding intervention strategies including pretreatment patient counseling and use of fertility preservation services.