NSD1 (also known as KMT3B) is a histone methyltransferase shown to methylate lysine 36 of histone H3 and lysine 20 of histone H4. NSD1 is a described as an intermediary transcription factor and depending on its cellular context, it is able to either negatively or positively influence transcription. Expression of this gene has been described in skeletal muscles, kidneys, adult and fetal brain, thymus and spleen. Heterozygous mutations and deletions of the NSD1 gene are associated with Sotos Syndrome, an autosomal dominant condition characterized by macrocephaly, tall stature, facial elongation, accelerated bone aging, and mental retardation.