July 9 (Reuters) - Rhythm Pharmaceuticals ( RYTM ) said

on Wednesday that its experimental drug to treat a rare form of

obesity helped patients reduce weight in a small study, sending

shares of the company 9% higher in premarket trading.

The drugmaker tested its treatment, bivamelagon, in a

study of 28 patients aged 12 years or elder who were suffering

from acquired hypothalamic obesity, which occurs after damage to

the hypothalamic region of the brain.

Patients were randomly chosen to receive 200 milligrams,

400 mg or 600 mg of the drug or a placebo for 14 weeks.

Eight patients who got the highest dose of the drug

showed a reduction of 9.3% in their body mass index, a common

measure of body fat based on a patient's height and weight.