Calcium-binding proteins (CaBPs) are a subfamily of calmodulin-like proteins, that modulate presynaptic calcium-dependent interactions with voltage-gated calcium channels. CaBPs play crucial roles in the development of normal sensorineural structure and function in both the visual and auditory systems. Disruption of CaBPs can result in a range of synaptic disorders of varying severity, which are dependent on the proteins or isoforms that predominate the affected system. In the retina, CaBP4 seems to be the isoform that is most important for the development of structure and function of the photoreceptor to ON bipolar synapse. Absence of CaBP4 results in synaptic ribbon immaturity in the first retinal synapse, disruption of ON-bipolar cell-driven responses, and a structurally thin outer plexiform layer. It has recently been demonstrated that at least some of the functional and anatomic disruption caused by CaBP mutations can be successfully addressed with gene augmentation therapy both in the eye and ear.