Provided are compositions and methods for use in polycystic ovary syndrome diagnosis (PCOS). The method involves a sample from a subject for a DENND1A Variant 2 mRNA or DENND1 A Variant 2 protein to make or aid in a diagnosis of PCOS. Also provided are methods for selecting an individual as a candidate for therapy for polycystic ovary syndrome by testing a biological sample from an individual for DENND1 A Variant 2 mRNA or DENND1 A Variant 2 protein and designating the individual as a candidate for the PCOS based on determining DENND1 A Variant 2 mRNA or DENND1 A Variant 2 protein in the sample. Also provided are products for use in aiding diagnosis of PCOS which contain reagents for detecting DENND1 A Variant 2 mRNA or DENND1 A Variant 2 protein, and packaging containing printed material describing use and indications for the product.