Microdeletions in 9q33.3-q34.11 in five patients with intellectual disability, microcephaly, and seizures of incomplete penetrance: is STXBP1 not the only causative gene?

Background Most microdeletions involving chromosome sub-bands 9q33.3-9q34.11 to this point have been detected by analyses focused on STXBP1, a gene known to cause early infantile epileptic encephalopathy 4 and other seizure phenotypes. Loss-of-function mutations of STXBP1 have also been identified in some patients with intellectual disability without epilepsy. Consequently, STXBP1 is widely assumed to be the gene causing both seizures and intellectual disability in patients with 9q33.3-q34.11 microdeletions.