Mongolism is a kind of mental subnormality.The disease is called Mongolism because the infant has features of Mongolian person.In order to avoid confusion Mongolism is called as Down's Syndrome.Mongolism is due to defect in the number of chromosomes present .Instead of having 46 chromosomes they have 47 chromosome .The additional chromosome is due to trisomy of chromosome 21.
It is seen that Mongolism generally occurs in infants whose mothers are over the age of 35. In some cases Mongolism also occurs to infants whose mother are very young.It is also found that Mongolism occurs infants whose mothers had many abortions & uterine bleeding during pregnancy.
In case of monozygotic twins both the infants suffer from Mongolism.The brains of mongol is smaller than normal.With increasing age, the brain appears increasingly immature in comparison with the normal. They have also cardiac malformation.