How can the disease be treated?

Since obesity is the greatest health problem, litmiting food intake will help control that. Exercise will also help to increase the lean body mass.
Growth hormones have been used to improve agility and physical strength in Prader-Willi Syndrome Patients. But, there have been some concerns with the growth hormones regarding lung function, so you should discuss the growth hormone option with a doctor.
Tesosterone has been used to correct the small penis in an infant boy.
At Puberty, hormone replacement has been used to correct low levels of sex hormones.