CLDN2 and Bartsocas-Papas syndrome 1: In support of the notion that Cldn2 upregulation contributes to IC/BPS symptoms, we recently showed that the overexpression of Cldn2 in the umbrella cell layer increases the permeability of the urothelium to small ions, triggers an inflammatory process in the bladder mucosa and lamina propria, and increases voiding frequency (Montalbetti et al., 2015).