PLCD1 (phospholipase C delta 1) is a phosphatidylinositol-specific phospholipase C enzyme that mediates production of the second messengers diacylglycerol and inositol 1,4,5-trisphosphate 1, binding phosphatidylinositol 4,5-bisphosphate to regulate intracellular signaling 2. The enzyme is essential for trophoblast and placental development and plays critical roles in calcium homeostasis and intracellular movement. PLCD1 functions as a tumor suppressor in multiple cancer types. In breast cancer, PLCD1 is frequently downregulated through promoter methylation (52-78% of tumors), and ectopic expression inhibits proliferation, induces apoptosis, and triggers G2/M cell cycle arrest 34. Similarly, in esophageal squamous cell carcinoma, PLCD1 suppresses proliferation, invasion, and migration via inhibition of Wnt/β-catenin signaling 5. In cardiovascular disease, the MIR503HG/miR-191-5p/PLCD1 pathway regulates apoptosis and inflammation in abdominal aortic aneurysm 6. Germline PLCD1 mutations cause non-syndromic congenital nail disorder and familial skin appendage tumors. Gain-of-function variants increase enzymatic activity, promoting keratinocyte proliferation through PKC/PKD/ERK1/2 pathway activation and TRPV6 channel closure, leading to pilomatricomas 7. PLCD1 knockout mice exhibit progressive hair loss and hair follicle abnormalities, demonstrating its essential role in hair development 8.