Phase I, open-label, single-arm, single-dose, trial of VGM-R02b (gene replacement therapy) in patients with Glutaric Acidemia Type I (GA-I) who meet enrollment criteria and are genetically confirmed by GCDH gene mutation. 1 to 3 patients aged≤ 6 years at the time of screening will be enrolled in each dose group in the dose escalation part. In the dose expansion part, the sample size will be statistically calculated and adjusted according to the efficacy and safety data in the dose escalation part.