RBP4 and ovarian disorder: Recently, RBP4 has been detected in serum, plasma, liver, adipose, and kidney samples, and dysregulation of RBP4 has been associated with a variety of diseases [17,19,46,47,48], including ovarian diseases, such as PCOS and ovarian cancer in humans [17,18,49,50,51] and ovarian cysts in swine [33].