Ipsen SA said the U.S. Food and Drug Administration partially halted phase 2 and phase 3 trials evaluating its drug palovarotene in patients with rare bone disorders under the age of 14, citing safety concerns.

Following the news, the company stock price fell 13.6% to close at €84.05 on the Euronext Paris stock exchange.

The French pharmaceutical company was testing palovarotene for treating fibrodysplasia ossificans progressiva, or FOP, which has no cure or treatment, as well as multiple osteochondromas, which is usually first diagnosed in patients around age 4. It also causes multiple benign tumors to develop on the bones, leading to limb deformity and restricted development as the children grow.

The decision applies to the patients under 14 who are part of palovarotene phase 2 trials — PVO-1A-202/204 and PVO-2A-201 — and a phase 3 trial called PVO-1A-301, Ipsen said in a Dec. 6 press release.

The FOP trials will continue for patients above the age of 14. However, the clinical studies evaluating palovarotene in patients with multiple osteochondromas primarily include children below the age of 14, so treatment will be stopped and no new patients will be added for the time being, the company added.

The U.S. FDA's decision is based on recent safety reports related to the trials, submitted by the French drugmaker. The company expects the regulator to request more information within the next month.

Ipsen had acquired palovarotene from Montreal-based Clementia Pharmaceuticals Inc. in a $1.31 billion cash deal in April.