C1QL4 is a secreted C1q-like protein with diverse roles in neural and non-neural tissues. Neurologically, C1QL4 binds with high affinity to the cell-adhesion G protein-coupled receptor BAI3 1, where it regulates synapse formation and density in the brain 1. The protein shows distinct spatial and temporal expression patterns in the developing and adult mouse brain, forming both homomeric and heteromeric complexes 2. Beyond the nervous system, C1QL4 promotes testosterone production in testicular Leydig cells through BAI3-dependent and BAI3-independent mechanisms involving ERK1/2 and cAMP/PKA signaling cascades 3. C1QL4 also stimulates endothelial cell angiogenesis via ERK1/2 phosphorylation 4. Clinically, elevated C1QL4 expression correlates with increased breast cancer malignancy and poor prognosis across molecular subtypes 5. C1QL4 was identified as a differentially expressed gene in recurrent glioblastoma multiforme 6. Additionally, C1QL4 gene hypermethylation was detected in coronary artery disease patients 7, suggesting potential epigenetic involvement in cardiovascular pathology. These findings indicate C1QL4 functions as a pleiotropic signaling molecule with implications in oncology and cardiovascular disease.