PPP1R17 (protein phosphatase 1 regulatory subunit 17) functions as an inhibitor of protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) complexes 1, playing critical roles in neurodevelopment and cellular signaling. In human neurodevelopment, PPP1R17 is a human-accelerated region (HAR)-regulated gene that has undergone remarkable rewiring of its expression patterns between primates and humans 2. Functionally, PPP1R17 slows neural progenitor cell cycle progression, paralleling the extended cell cycle length observed in primate and human neurodevelopment 2. PPP1R17 is a direct transcriptional target of NEUROG2, a proneural gene essential for neurogenesis, and is enriched in cells with NEUROG2 activity during cortical organoid development 3. The gene is expressed as a cerebellar marker in Purkinje cell layer development during cerebellar differentiation from human induced pluripotent stem cells 4. Clinically, PPP1R17 dysregulation is associated with tumorigenesis. In Cushing's disease, PPP1R17 overexpression reactivates a neurodevelopmental phosphoprotein program and drives tumor proliferation through PP2A inhibition; this phenotype is reversible using FDA-approved PP2A agonists 1. PPP1R17 is also identified as a prognostic biomarker in colon adenocarcinoma, pancreatic cancer, and potentially influences immune responses during chr7 parasitic infection 567.