Chromosome 22 is the third smallest of the 46 pairs of chromosomes in humans. It is considered to be very gene rich, with an estimated 2,000 genes. 15% of it's sequence has already been determined, and approximately 150 genes have been identified already. There are many different disorders involving chromosome 22, such as trisomy 22 (many variations such as trisomy 22 mosaic, partial trisomy 22, translocation of 11 & 22 or other orphan translocations involving chromosome 22 and another chromosome) Cat Eye Syndrome, VeloCardioFacial Syndrome, DiGeorge Syndrome, Ring 22 and other deletions and translocations. It has also been implicated in bi-polar disorder and schizophrenia.