The cadherin superfamily is a large family that engage in both homo- and heterotypic, calcium-dependent, cell-cell adhesion events, and can be divided into at least four subfamilies based on the extracellular (EC) regions and cytoplasmic domains, that is: classical cadherins, desmosomal cadherins, protocadherins, and cadherin-like molecules. Human cadherin 4, type 1, R-cadherin (retinal), also known as CDH4, CAD4 and RCAD, is a classical cadherin from the cadherin superfamily. It is a calcium-dependent adhesion molecule and a type I transmembrane glycoprotein composed of five extracellular cadherin repeats, a transmembrane region and a highly conserved cytoplasmic tail. CDH4 is thought to play an important role during brain segmentation and neuronal outgrowth, and also exerts critical actions in kidney and muscle development. CDH4 is expressed in vascular smooth muscle, pancreatic β-cells, thyroid follicular cells, sensory neurons of the dorsal root ganglia, and, possibly, astrocytes and endothelium of the retina. As a classic cadherin, CDH4 forms both homodimers and heterodimers with N-cadherin. The extracellular region of human CDH4 is 96% aa identical to that of mouse CDH4.