Trisomy 9

Full trisomy 9 is a rare and fatal chromosomal disorder in which cells carry three copies of chromosome 9 instead of the usual two. The condition can be survivable when the extra material is present in only some of the body cells, a pattern called mosaicism, or when only part of the chromosome is tripled, as in partial trisomy of the short arm, called trisomy 9p. In that partial form cells have the normal two whole copies of chromosome 9 plus an additional piece of the short arm, labelled p. The source therefore treats full, mosaic and partial trisomy as related states with very different outcomes.