This variant was classified as pathogenic according to American College of Medical Genetics and Genomics (ACMG) guidelines and fully encompassed the <i>KCNQ2</i> gene, leading to a definitive diagnosis of <i>KCNQ2</i>-related developmental and epileptic encephalopathy 7 (DEE7).<h4>Conclusion</h4>We diagnosed DEE7 caused by a large <i>KCNQ2</i> deletion using trio whole-exome sequencing and multiplex ligation-dependent probe amplification (MLPA). The gene discussed is KCNQ2; the disease is genetic developmental and epileptic encephalopathy.