Adhesion molecule that promotes lamina-specific synaptic connections in the retina. Expressed in specific subsets of interneurons and retinal ganglion cells (RGCs) and promotes synaptic connectivity via homophilic interactions. Homodimer; mediates homophilic interactions to promote cell adhesion. Up-regulated in glomeruli in HIV-associated nephropathy. In diseased glomeruli, significantly overexpressed and the expression is no longer restricted to mesangial cells but includes podocytes and parietal epithelial cells (PubMed:15213259). Ig-like C2-type domains 1 and 2 mediate homophilic interactions. Dysregulation of this protein may play an important role in podocyte dysfunction in HIV-associated nephropathy. Belongs to the sidekick family.