** Shares of gene therapy developer Lexeo Therapeutics LXEO.O rise 14% to $4.98

** Co says it finalized design of a key study for LX2006, a gene therapy for heart disease linked to Friedreich ataxia, a rare inherited disorder that damages nerves and the heart

** Says study will test if a one-time gene therapy can reduce thickened heart muscle, using MRI scans to track changes

** LXEO says 26 patients aged 16 plus to be enrolled; half get treatment, half untreated controls who may switch after six months

** Says U.S. FDA advised against using a placebo procedure in the trial design

** Adds patient enrollment to start by end-June; aims for approval filing in 2028 with data due in second half of 2027

** Including session's move, stock down ~50% YTD