Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. It is associated with profound insulin resistance resulting in a markedly increased risk for non-insulin dependent diabetes mellitus (NIDDM) at a strikingly early age (3rd-4th decades). The Specific Aims of this proposal are 1) To determine the role of insulin receptor serine phosphorylation in the pathogenesis of insulin resistance in PCOS. We hypothesize that increased insulin- independent insulin receptor serine phosphorylation inhibits insulin- induced receptor-mediated signaling in PCOS. This will be investigated by examiningthe effects of dephosphorylation on the kinase activity of insulin receptors partially purified from muscle and from fat, using serine specific (e.g., phosphate type 2A) as well as nonspecific (e.g., alkaline phosphatase) phosphates. 2) To determine whether increased insulin-independent serine phosphorylation of the insulin receptor is associated with decreased insulin-receptor mediated signaling in vivo in PCOS. This will be investigated by assessing insulin stimulation, in vivo and in intact adipocytes, of insulin receptor substrate-1 (IRS-1) phosphorylation and phosphatidylinositol 3-kinase (PtdIns 3-kinase) activity. Muscle insulin-responsive glucose transporter (GLUT4) content will also be examined to determine if abnormalities in insulin signaling affect its abundance. 3) To determine whether defects in insulin action in PCOS are genetic. If insulin resistance in PCOS is a genetic defect, first degree relatives should be affected. This will be investigated by determining total body and cellular insulin action in brothers of PCOS probands. We will screen for mutations in the insulin receptor and IRS-1 genes of PCOS women with denaturing gradient gel electrophoresis or single-stranded confirmation polymorphisms.