Adverum Biotechnologies Inc. is quitting development of a phase I/II gene therapy for alpha-1 antitrypsin deficiency (A1ATD) and abandoning plans to submit an investigational new drug application for another candidate employing the same capsid after the A1AT trial failed to show clinically meaningful protein expression. Company shares (NASDAQ:ADVM) fell $1.21, or 26.6 percent, to $3.34 on Friday.