ADAD1 (adenosine deaminase domain containing 1) is an RNA-binding protein essential for male fertility and germ cell function. It contains an adenosine deaminase domain and catalyzes adenosine-to-inosine editing in double-stranded RNA 1, functioning in RNA processing and modification pathways. ADAD1 is required for spermatogonial stem cell maintenance and meiotic progression; zebrafish adad1 mutants develop sterile phenotypes with failure of spermatocytes to progress beyond zygotene stage and eventual germ cell loss 2. In humans, novel biallelic and homozygous missense variants in ADAD1 have been identified in infertile patients with impaired spermatogenesis, characterized by abnormal sperm morphology and disrupted expression of ADAD1 and interacting proteins like DNAH17 3. Beyond reproductive function, ADAD1 genetic variants influence immune responses: the A allele of rs17388568 increases risk for high-grade immune-related adverse events in PD-1/PD-L1 inhibitor-treated cancer patients 4, and the same variant is associated with reduced risk of joint limitation of motion in juvenile idiopathic arthritis 5. ADAD1 is also implicated as an immune-related gene associated with colon cancer prognosis 6. These findings establish ADAD1 as a multifunctional regulator of both reproductive and immune processes.