Neurodevelopmental disorders (ND) have an important prevalence in children; intellectual disability in particular occurs in a heterogeneous group of genetic conditions. The evolution of molecular cytogenetic techniques and the recent advances in exome sequencing technologies have enormously implemented the possibilities of diagnostic classification in children with cognitive disabilities due to genetics. The paper presents the case of a patient with a neurodevelopmental disorder who was diagnosed with Kleefstra (KS) syndrome, caused by a point mutation de novo of EHMT1 gene.