Down syndrome is the most common chromosomal disorder which causes mental retardation.
Chromosomal disorder is an abnormality in numbers and/or structure of chromosomes.
Normal chromosome
 |
 |
normal female
karyotype 46,XX |
normal male
karyotype 46,XY |
The most common congenital malformations and frequent cause of mental retardation is "Down Syndrome".
The overall incidence is 1 in 600 and rises significantly for pregnant women age 35 and over. |