In 1959 Lejeune and his colleague first demonstrated a chromosome abnormality and showed that " infant mongoliens " had 47 instead of the normal 46 chromosomes in their body cells. Recent studies show that about 1 in 200 infants have recognisable chromosome abnormalities.Trisomy 21 ( Down syndrome, DS ) trisomy 18 ( Edwards syndrome, ES ) and trisomy 13 ( Patau syndrome, PS ) have been found to be the most common trisomies with population incidences of approximately 1 in 650, 1 in 8000 and 1 in 10000, respectivevely.
