Here, we focus on the endothelial tight-junction protein claudin-5 (CLDN5), because the CLDN5 gene is mapped to the schizophrenia-associated 22q11.2 deletion region, and a single nucleotide polymorphism in the CLDN5 locus is also linked to schizophrenia. The gene discussed is CLDN5; the disease is schizophrenia.