PCDHA4 (protocadherin alpha 4) is a calcium-dependent cell adhesion molecule that functions as a synaptic cadherin involved in neuronal recognition and connection specificity 1. The protein undergoes presenilin-dependent intramembrane proteolysis following matrix metalloprotease cleavage, generating cytoplasmic fragments that may participate in intracellular signaling 2. PCDHA4 can form heteromers with gamma-protocadherins, which alters their processing susceptibility and potentially modulates synaptic adhesive properties 2. The gene is part of a clustered protocadherin family with a unique genomic organization featuring variable and constant region exons 3. Disease relevance includes its identification as a tumor suppressor in metastatic rhabdomyosarcoma, where DNA hypermethylation silences PCDHA4 expression and correlates with increased cell proliferation and invasiveness 4. PCDHA4 methylation also serves as a diagnostic marker for cervical cancer progression 5. Additionally, hippocampal PCDHA4 expression shows significant association with Alzheimer's disease risk through transcriptome-wide association studies 6, and the gene is implicated in amblyopia susceptibility 7. These findings suggest PCDHA4 plays critical roles in both normal neurodevelopment and various pathological conditions.