Key proteins associated with sperm function, such as NPC intracellular cholesterol transporter 2 (NPC2), galectin-3-binding protein (LGALS3BP), lipocalin-1 (LCN1), and prolactin-inducible protein (PIP), show reduced expression in oligoasthenoteratozoospermia (OAT) [31]. The gene discussed is NPC2; the disease is oligoasthenoteratozoospermia.