Wiedemann-Steiner syndrome results from mutations in the MLL (also known as KMT2A) gene on the long arm of chromosome 11. The condition is autosomal dominant, meaning that only one abnormal copy of the gene is needed for a person to have the syndrome. In a majority of cases to date, the mutation occurred de novo — that is, neither parent was affected and the mutation is sporadic. Offspring of those with WSS have a 50% chance of having WSS.