Mouse models of cognitive disabilities in trisomy 21 (Down syndrome).

Trisomy 21 (TRS21), also referred to as Down syndrome, occurs once in every 800-1,000 live births. It is the consequence of an extra copy of HSA21 that causes an imbalanced gene dose effect. TRS21 is the first known genetic cause of cognitive disability. The syndrome is complex, and includes various cardiac, immune, and bone disorders. Most of these signs are highly variable in expression but cognitive disability is the most constant characteristic of persons with TRS21. The syntenies that exist between HSA21 and three mouse chromosomes (MMU10, MMU16, and MMU17) offer the opportunity for a genotype-phenotype correlation. We present here the segmental trisomies available in the mouse and we discuss their contribution to the brain and cognitive phenotypes of TRS21.