An A to Z glossary of disabilities

A rare chromosomal condition where the entire eighth chromosome, known as trisomy, appears three times instead of twice

There are three types of Trisomy 9, Full trisomy 9: All of the cells in the baby's body and placenta have three copies of chromosome 9.Partial trisomy 9: There are two full copies of the ninth chromosome plus an additional partial copy.Mosaic trisomy 9: Trisomy is present in some of the body's cells while other cells have a normal set of chromosomes.

Symptoms include characteristic facial appearance, vision loss, dislocated joints, underdeveloped genitalia, kidney cysts, feeding and breathing difficulties, short stature and development delays.

In most cases, trisomy 9 appears to occur randomly rather than as a result of specific, identified risk factors.