This study is a first-in-human, open-label, safety, tolerability, and efficacy study in adult patients with Gaucher disease Type 1. The aims are to investigate the safety/tolerability and efficacy of FLT201, and to investigate the relationship of FLT201 dose to augmentation of residual glucocerebrosidase (GCase) expression (activity and concentration), and its potential to improve the clinical phenotype by reduction and prevention of cellular accumulation of GCase substrate.