KANSL1 haploinsufficiency caused by heterozygous pathogenic genetic variants in KANSL1 is associated with the neurodevelopmental disorder Koolen-de Vries syndrome (KdVS; OMIM no. 610443).65 Pathogenic variants in KAT8 have also been associated with developmental disorders inclusive of a strong neurological phenotype,66 underpinning the functional importance of the NSL complex in neurodevelopment. Here, KANSL1 is linked to Koolen-de Vries syndrome.