Interestingly, phenotypic comparison of both the 17q21.31 microdeletion and KANSL1 heterozygous mutation patients show similar clinical severity, implicating that haploinsufficiency of KANSL1 is sufficient to cause the full manifestation of KdVS phenotype[3, 13–15]. The gene discussed is KANSL1; the disease is Koolen-de Vries syndrome.