PROK2 and major depressive disorder: Spijker et al. (2010) studied the peripheral blood of 21 patients with MDD and 21 healthy control participants and found significant differences in the expression levels of CAPRIN1, CLEC4A, CKRT23, MLC1, PLSCR1, PROK2, and ZBTB16, indicating that this signature could distinguish patients with depression from healthy individuals.