** Drug developer Neurogene's shares fall 19% to $28 premarket

** Company says it has paused testing high-dosage version of its experimental gene therapy after reporting a serious treatment related side-effect in one of the participants

** Neurogene says the participant is in critical condition due to hyperinflammatory syndrome, a rare and life-threatening immune response

** The gene therapy, NGN-401, is being developed to treat Rett syndrome, a rare genetic neurological disorder that occurs most often in girls and affects their ability to speak, walk, eat, and even breathe easily

** Company says the U.S. Food and Drug Administration has allowed the early-mid-stage study to continue testing patients with the low-dosage version

** As of last close, stock up 78% YTD

(Reporting by Mariam Sunny in Bengaluru) ((Mariam.ESunny@thomsonreuters.com))