DPP4 and polycystic ovary syndrome: The following is how the FerSig risk prognostic signature was established based on prognostic data and 5 ferroptosis proteins as follows: FerSig (PCOS)= 0.00111362055530056 × expr (G6PD) + 0.000645037118531247 × expr (DPP4) - 0.00217906042357578 × expr (GPX4) + 0.000140537487448025×expr (PCBP1) + 0.000131772720458687 × expr (PCBP2).