[1] Prior to 2015, when whole genome sequencing was used to identify some genes involved in NCS, the condition was labelled "Syndrome X" when it was first discovered in Brooke Greenberg.
In five patients, coding de novo mutations were found in five different genes which fall into similar functional categories of transcription regulation and chromatin modification.
This region appears to have regulatory functions (histone acetylation and DNase I hypersensitivity) and is in close proximity to several genes (AP1S2, MRX59, MRXSF, MRXS21, MRXS5 and PGS) involved in mental retardation.
[1] An 1888 article in the newspaper The Diamond Drill of Crystal Falls, Michigan, describes a 17-year-old girl from Stockerau, Vienna, named Maria Schumann.
Due to her condition (identified at the time as "microcephaly"), she had never outgrown the mental state or size of an infant, but was of "sound composition".