To date, over 250 genes have been reported to have strong association with NDD.58 A very small number of genes (SCN2A, CHD8, STXBP1) and loci (16p11.2 microdeletion, 15q13.3 microdeletion etc.)that are found to be enriched within NDD are still below the level of 1% frequency threshold.48,59–61 The current clinical genetic diagnostic yield for severe, syndromic NDDs associated with ID is approximately 40% and it is higher if genome sequencing data are available for other members (parents, siblings) of the family.62 Here, STXBP1 is linked to Neurodevelopmental delay.