WNT9B is a secreted Wnt ligand that activates canonical (β-catenin-dependent) and non-canonical Wnt signaling pathways 1. As a frizzled receptor ligand, WNT9B plays critical roles in embryonic development, particularly in kidney and urogenital tract morphogenesis, where it activates signaling cascades in metanephric mesenchyme to induce tubulogenesis and acts upstream of WNT4 in tubule formation 1. WNT9B is essential for craniofacial development and palatal fusion; mutations cause nonsyndromic cleft lip and palate through epigenetic mechanisms involving retrotransposon-mediated transcriptional interference 2. In adult tissues, endothelial cell-derived WNT9B maintains hepatic metabolic zonation and supports liver regeneration via β-catenin signaling; Wnt activators rescue liver function in acute liver failure models 3. Clinically, homozygous WNT9B variants are associated with bilateral renal agenesis/hypoplasia/dysplasia in humans 4, and common WNT9B polymorphisms associate with Mayer-Rokitansky-Küster-Hauser syndrome risk through gene-gene interactions 5. Genome-wide association studies identify WNT9B variants linked to cardiac age acceleration and adverse cardiovascular outcomes 6. These findings establish WNT9B as a developmental regulator with therapeutic potential in regenerative medicine and organ dysfunction.