Down syndrome is a genetic mutation.
A cancer syndrome or family cancer syndrome is a genetic disorder in which inherited genetic mutations in one or more genes predispose the affected individuals to the development of cancers and may also cause the early onset of these cancers . Down syndrome ( DS or DNS ) , also known as trisomy 21 , is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21 . In 1957 , the genetic cause of Down syndrome , an extra copy of chromosome 21 , was discovered .