(Reuters) – Regeneron Pharmaceuticals Inc said on Thursday its experimental treatment for a very rare genetic bone disorder showed a nearly 90% reduction in new lesions compared to placebo, in a mid-stage study.

The drugmaker said it plans to use detailed results from the trial as the basis of regulatory submissions and that it would also conduct a study in children with FOP.

The drug, garetosmab, tested in patients with fibrodysplasia ossificans progressiva (FOP), reduces the formation of bone lesions by neutralizing a protein called Activin A.

The protein is critical to heterotopic ossification, a process where the muscles, tendons and ligaments of FOP patients are progressively replaced by bone.

FOP leads to abnormal bone formation resulting in skeletal deformities, progressive loss of mobility and premature death, and has no approved treatments, the drugmaker said.

There are only about 800 patients diagnosed with the disorder worldwide and most of them are wheelchair bound by the age of 30, the company said. FOP patients, on average, live as long as 56 years.

(Reporting by Manojna Maddipatla in Bengaluru; Editing by Shinjini Ganguli)