In the study, we present the clinical and mutational characteristics of additional 10 Chinese patients with MRD5 identified by next-generation sequencing (NGS) from a clinical cohort of 1,986 cases with NDDs manifesting ID, DD, epilepsy, and ASD between January 2014 and May 2022 in Shandong Province of China, and five novel mutations in the SYNGAP1 gene were discovered. The gene discussed is SYNGAP1; the disease is dentin dysplasia.