CPNE9 (copine family member 9) is a calcium-dependent phospholipid-binding protein located on chromosome 3 that likely plays roles in calcium-mediated intracellular signaling and dendrite formation. The protein contains domains enabling calcium-dependent phospholipid binding and cellular responses to calcium ions, with evidence suggesting involvement in dendrite extension. In multiple myeloma, CPNE9 expression serves as a favorable prognostic indicator; patients with higher CPNE9 expression demonstrate significantly longer event-free survival (EFS, P=0.0065) and overall survival (OS, P=0.016), with CPNE9 acting as an independent positive predictor for EFS (P=0.002) 1. Disease relevance extends to developmental disorders, as CPNE9 disruption through chr3 rearrangements has been identified in syndromic intellectual disability 2. A 12-kb copy-neutral inversion disrupting CPNE9 was detected via long-read sequencing in monozygotic twins with intellectual developmental disorder with dysmorphic facies and ptosis, indicating CPNE9's importance in neurodevelopmental processes 2. Additionally, CPNE9 promoter disruption through interchromosomal insertion has been associated with multiple congenital anomalies, suggesting potential position effects on gene regulation 3. These findings establish CPNE9 as both a prognostic biomarker in hematologic malignancy and a developmentally critical gene.