Dysregulated RAC1 activity causes synaptic function defects leading to neurodevelopmental disorders (NDDs), which manifest as intellectual disability, learning difficulties, and language disorders.<h4>Case presentation</h4>Here, we reported two cases with <i>TRIO</i> variation from one family and three cases with <i>CNKSR2</i> variation from another family. The gene discussed is CNKSR2; the disease is language disorder.