Causes of Down syndrome are predictable at 1 per 800 to 1000 births. Maternal age develops the chance of conceiving an infant with symptoms of Down syndrome. Mostly children born out of mothers over the age of 35 develops Down syndrome symptoms. Women of this age group reflect overall fertility and thereby have the increased risk of giving birth to babies with Down syndrome characteristics. Generally 80% of Down syndrome children are born from mothers of this age group.

Beside this, there are four other basic causes of Down syndrome as follows:

(1)Trisomy 21 is a cause of Down syndrome where a child inhibits three copies of every gene.

(2)Robertsonian translocation is another cause of Down syndrome which is also referred as familial Down syndrome.

(3)A nondisjunction occurrence during the early stages of cell development changes the normal arrangement of the chromosome thereby leading to Down syndrome.

(4)Lastly, when chromosome 21 undergoes a replica incident thereby creating extra copies of the chromosome causes Down syndrome.

Thus the causes of Down syndrome are spontaneous, by and large having no preventive measures.