<h4>Background</h4>Mutations in the <i>KMT2C</i> gene can cause Kleefstra syndrome-2 (KLEFS2).<h4>Case</h4>In this study, we analyzed the clinical, genetic testing, and 10-year follow-up data of a child with KLEFS2 treated at the Child Healthcare Department, Children's Hospital of Nanjing Medical University, Nanjing. Here, KMT2C is linked to Kleefstra syndrome 2.