Down syndrome

People with Down syndrome usually have a life span shorter than normal.Down syndrom was named after John Longdon Down,who characterized the syndrome in 1866.What causes Down syndrome? Normal human has 23 chromosomes pairs.They are numbered from 1 to 23.
So all together normal human has 46 chromosomes.People with Down syndrome have instead of 46 chromosomes one more chromosome number 21,so instead two chromosomes 21they have three chromosome 21.This condition is called trisomy 21. Trisomy 21 is the most common chromosome number abnormality. People with Down syndrome exhibit varying mental retardation. However,some individuals with the syndrome live to midle age or beyond,and many are socially adept and able to hold jobs. A few women with Down syndrome have had children,though most people with the syndrom are sexually underdeveloped and sterile.