NPC2 and Azoospermia: Yamakawa et al. compared seminal plasma from fertile and non-fertile men with 2-dimensional electrophoresis and LC-MS/MS and found 4 proteins (stabilin 2 STAB2, 135-kD centrosomal protein, CP135, guanine nucleotide-releasing protein GNRP, and prolactin-inducible protein PIP) as potential biomarkers for NO azoospermia and 1 protein [epididymal secretory protein E1 (NPC2)] as a potential biomarker for obstructive azoospermia.