What causes Downs Syndrome?

The most common cause of Down syndrome occurs when an infant is born with three, rather than two, copies of the 21st chromosome (known medically as trisomy 21).

It is this extra genetic material in infants with Down syndrome that disrupts their physical and cognitive development. Although many theories have been developed, it is not known what actually causes Down syndrome. Some professionals believe that hormonal abnormalities, X-rays, viral infections, immunologic problems, or genetic predisposition may be the cause of the improper cell division resulting in Down syndrome.

It has been known for some time that the risk of having a child with Down syndrome increases with advancing age of the mother; i.e., the older the mother, the greater the possibility that she may have a child with Down syndrome. However, most babies with Down syndrome (more than 85 percent) are born to mothers younger than 35 years. Some investigators reported that older fathers might also be at an increased risk of having a child with Down syndrome.

It is well known that the extra chromosome in trisomy 21 could either originate from the mother or the father. Why Down syndrome occurs is a mystery. It can happen to anyone.