ABSTRACT
A normal human karyotype has a complement of 46 chromosomes (22 autosomal pairs and one pair of sex chromosomes XX or XY). Down’s, Turner’s and Klinefelter’s syndromes were the first chromosome abnormalities identified, in 1959. With the advent of new molecular techniques many more chromosomal abnormalities have now been identified. Chromosomal abnormalities occur in approximately 6 per 1000 live births. The true incidence post conception is higher than this, but many result in spontaneous abortion. A chromosomal abnormality usually gives rise to multiple congenital malformations. Many can now be detected on prenatal testing, by ultrasound and amniocentesis.
