DDC and constipation disorder: The improvement in motor symptoms in the synbiotic treated group could be explained by modification of the gut microbiota, which plays an important role in l-dopa bioavailability (Cheng et al. 2024), as well as by improving gut motility and hastening up gastric transit time, as it was proved that constipation delays gastric emptying and therefore submits l-dopa to more exposure and metabolism by peripheral dopa decarboxylase (Leta et al. 2023).