ZP1 and Empty ovarian follicle: Mutations on the ZP genes, including a homozygous mutation in ZP1, heterozygous mutations in ZP1 or ZP3, or a compound mutation in ZP2, may negatively influence the normal development of oocytes along with the normal formation of ZP, resulting in oocyte degeneration and even the empty follicle syndrome (EFS), thus compromising female fecundity [3,8,17,22,26,27,28].