** Shares of drugmaker Rhythm Pharmaceuticals RYTM.O rise 1.7% to $106.50 premarket

** Co says its experimental therapy for a rare disease showed positive results in a mid-stage study

** The company was testing the therapy to treat a genetic disorder called Prader-Willi syndrome $(PWS)$ in 18 patients aged 6-65 years old

** A key feature of PWS is a constant sense of hunger that usually begins at about two years of age

** Co says the therapy called setmelanotide helped reduce body weight and hyperphagia- feelings of intense and persistent hunger in patients at three months and six months

** Co plans to advance setmelanotide into a late-stage trial in PWS, pending successful completion of this trial

** Up to last close, stock up 87.2% YTD

(Reporting by Sneha S K)

((Sneha.SK@thomsonreuters.com;))