Insulin resistance and related hyperinsulinaemia is actually a very common feature affecting about 65–70% of women with PCOS;73 it is seen most frequently in obese patients, affecting 70–80%, compared with only 20–25% of lean PCOS sufferers.72 Despite this observation, insulin resistance and hyperinsulinaemia appear to be linked to PCOS independently of obesity, and modifications in the normal cellular mechanisms of insulin signalling have been demonstrated in both lean and obese patients. The gene discussed is INS; the disease is polycystic ovary syndrome.