Shares of the New Jersey-based company fell more than 13% to $18.51 premarket on the news.
The Food and Drug Administration (FDA), through a so-called complete response letter, has sought additional information related to certain processes for the gene therapy, called Kresladi, to complete its review.
Rocket was seeking its first approval from the agency to use the therapy in treating patients with severe Leukocyte Adhesion Deficiency-I (LAD-I).
In these patients, the white blood cells cannot stick properly to blood vessel walls of an infection site due to a mutation in the protein-encoding ITGB2 gene. This could lead to severe immune system deficiencies and recurrent infections.
In February, the agency had extended its timeline to decide on approval for the therapy in order to review similar data related to certain processes for the gene therapy.