TFF3 and velopharyngeal dysfunction: Therefore, longitudinal cohort studies are needed in the future to explore the alterations of the three serum biomarkers (TFF3, ChE and Hcy) during the disease progression in PDD and VPD; (4) genetic factors such as the TFF3 genotype and folate or cholinesterase inhibitor administration were not considered in this study; (5) to validate and complete the questionnaire, we chose only PDD and VPD patients with sufficient cognitive ability, which significantly narrowed the study population.