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Chromosomal Abnormalities
Chromosomal abnormalities – sometimes also called cytogenetic disorders – are very common. Although we don´t see many affected people. Most fetus with some chromosomal abnormality usually do not survive. About 50% of first–trimester abortions is connected with some cytogenetic mistake. The incidence of chromosomal abnormalities is approximately 1 out of 200 of newborns. We recognize two types of chromosomal abnormalities: Numeric and Structural. We are able to find the disorders due to karyotype testing. The cytogeneticists get the samples (blood, amnionic fluid), then stain the chromosomes and arrange them in the right order by their length. Then we can see some changes in pattern (banding). The most typical method is Giemsa stain, so it is usually called "G banding". This is important for structural abnormalities. Numeral abnormalities we can identify even easier.

Other classification of chromosomal abnormalities depends on fact which type of chromosome is affected – autosomes (Down syndrome, DiGeorge syndrome) or sex chromosomes (Klinefelter syndrome, Turner syndrome).