What causes polycystic ovarian disease and what can be done to treat the cause?

Obesity. The majority of cases of pcos occur in overweight women. Weight loss is very effective for restoration of the normal menstral cycle. However, many women are unable to lose weight and require other treatments such as ocp's or surgery.
Insulin resistance. Pcos has a genetic component; we don't know all the genes yet - and is influenced by enviromental factors and lifestyle including obesity, activity levels. Insulin resistance/ 'pre-diabetes' may be the first thing that 'goes wrong' in pcos. The closest we have to treating the cause is losing weight, regular exercise (cardio + weights) & insulin-sensitizing drugs like metformin. Surgery is obsolete.