Introduction

Synonyms: Trisomy 21:Mongol child: Mongolian idiocy

What is Down syndrome?
Down syndrome, a chromosomal disorder, occurs when, instead of the normal complement of 2 copies of chromosome 21, there is a whole, or sometimes part of an, additional chromosome 21.

Incidences:
Approximately 1:700 live births (Recently reported as 1:1000 or 1:1100)

Causes:

Down syndrome is caused by an error that occurs during the formation of the twenty-first chromosome. Its occurrence is sporadic and the parents are usually unaffected. The factors, which adds to the increasing incidence of this disorder are

• use of various approaches for prevention of pregnancies
• Amniotic fluid examination
• Elderly mother, though the majority of children with Down syndrome are born to younger mothers.
  

However, in a minority of cases (3-4 per cent) a mother may have a balanced translocation of chromosome 21. In these cases the condition is inheritable.