June 12 (Reuters) - Rein Therapeutics ( RNTX ) has

paused patient enrollment and dosing in a mid-stage trial of its

lung disease drug in the U.S. after the Food and Drug

Administration placed a clinical hold, the drug developer said

on Thursday.

Shares of the company fell nearly 10% after the bell.

The company was testing a drug named LTI-03 to treat

patients with idiopathic pulmonary fibrosis (IPF). The disease

causes scarring of the lungs that makes it harder for them to

work properly.

Rein said in a filing that it is actively working with

the FDA to remove the clinical hold.

The FDA and Rein did not immediately respond to Reuters'

requests for comment on why the hold was placed.

The drug was well-tolerated and safe in an early-stage

study in patients with IPF, the company said in the filing. No

drug-related serious adverse events have been reported in any

studies treating patients with LTI-03, it added.

Rein continues to study the drug and enroll patients in

Australia and Europe.