CDH18 (cadherin 18) is a calcium-dependent cell adhesion protein that mediates homophilic cell-cell interactions and contributes to cell sorting through adherens junction formation and organization 1. As a classical cadherin, CDH18 participates in beta-catenin binding and catenin complex formation, facilitating calcium-dependent cell-cell adhesion and cell-cell junction assembly [UniProt annotation]. The protein is involved in fundamental cellular processes including cell migration, cell morphogenesis, and plasma membrane localization. CDH18 has demonstrated relevance in reproductive biology, where it is expressed in normal testicular tissue. Studies of azoospermic (non-fertile) testes revealed abnormal Sertoli-germ cell tight junctions accompanied by downregulation of CDH18 expression in 37.5% of azoospermic samples 2, suggesting CDH18 dysfunction may contribute to male infertility through disrupted spermatogenesis. Genome-wide association studies have linked CDH18 to neuropsychiatric disorders including bipolar disease and schizophrenia 1, implicating CDH18 in neural circuit development and synaptic function. The gene's role in brain development, neuronal migration, and synapse formation suggests that CDH18 dysfunction may alter neural connectivity in psychiatric disease. However, disease-causing mutations specific to CDH18 have not yet been definitively established, distinguishing it from other cadherins like PCDH19 with confirmed pathogenic variants.