The four novel proteins identified in the present investigation as selectively expressed in islet cells (CFC1, FAM159B, RBPJL and RGS9) are unlikely to be specific for beta cells, as expression was observed in islets of both non-diabetic and T2D subjects as well as in islets of T1D subjects that lack beta cells. Here, RBPJL is linked to type 1 diabetes mellitus.