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Down syndrome, Down's syndrome, or trisomy 21 is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome.

It is named after John Langdon Down, the British doctor who described the syndrome in 1866. The disorder was identified as a chromosome 21 trisomy by Jérôme Lejeune in 1959. The condition is characterized by a combination of major and minor differences in structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth as well as facial appearance. Down syndrome in a baby can be identified with amniocentesis during pregnancy or at birth. The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although these statistics are heavily influenced by the age of the mother.

Individuals with Down syndrome may have some or all of the following physical characteristics:
Oblique eye fissures with epicanthic skin folds on the inner corner of the eyes, muscle hypotonia (poor muscle tone), a flat nasal bridge, a single palmar fold, a protruding tongue (due to small oral cavity, and an enlarged tongue near the tonsils), a short neck, white spots on the iris known as Brushfield spots, excessive joint laxity including atlanto-axial instability, congenital heart defects, excessive space between large toe and second toe, a single flexion furrow of the fifth finger. Most individuals with Down syndrome have mental retardation in the mild (IQ 50–70) to moderate (IQ 35–50) range. In addition, individuals with Down syndrome can have serious abnormalities affecting any body system. They also may have a broad head and a very round face.

On March 21st, 2009, World Down Syndrome Day will mark the 50th anniversary of the publication of Professor Jerome Lejeune's discovery of the extra copy of chromosome 21 which causes Down syndrome.

This is the logo which celebrates this day

Below are a few international posters that were released to embark this day.

Initiated by:
Rotaract Club of Mumbai Ghatkopar
Source:
http://downsyndrome.in/health_progamme.php
http://www.worlddownsyndromeday.org