Chromosomal Abnormalities

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Chromosomal abnormalities - sometimes also called cytogenetic disorders - are very common at all. Although we don´t see many affected people. How it is possible? The fetus with some chromosomal abnormality is usually not able to survive. About 50% of first-trimester abortions is connected with some cytogenetic mistake. The incidence of chromosomal abnormalities is approximately 1 from 200 of newborns. .

We recognize two types of chromosomal abnormalities:

1. numeric
2. structural

We are able to find the disorders due to karyotype testing. The cytogeneticists get the samples (blood, amnion fluid), then stained the chromosomes and put then 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 banging". This is important for structural abnormalities. Numeral abnormalities we could find even easier.

Otherwise 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).

Types of Structural Abnormalities

Ring chromosome

Deletion

Inversion

Isochomosomes

Translocation

Deletion

• Deletion is characterized by the lost of some part of chromosome. Two breaks have to occur for deletion of the interstitial segment. For deletion of terminal segment (telomere) one break is enough. Segments which were deleted from the chromosome are not able to "live" on their own. It is the reason why we lost genes which were coded by these part of chromosome.
• One special example of deletion exists. It is called "ring chromosome". It is a situation when chromosome lost both of its ends. The long and the small arms then connect together and chromosome became a ring shaped.

Inversion

• For inversion are typical two breakages in the different part of the chromosome. The newly created segments then replace each other.

Isochromosomes

• Isochromosomes are created by the incorrect divides of centromere. Normally centromere divides vertically. In this case they divide horizontally. The result is usually the lost of one arm. It means that newly created chormosome has just two long arms or two short arms which are normally connected by centromere. We could find it on X chromosome very often. It is a huge problem during the fertilization. Because fetus then get a trisomy for one arm and a monosomy for the second arm.

How We Denoted Parts of a Chromosome

Related articles

• Karyotype
• Disorders of the Autosomes
• Disorders of the Sex Chromosomes
• The Sex Chromosomes and Sex Determination

Sources

• KUMAR, ABBAS, FAUSTO, MITCHELL,, et al. Robbins Basic Pathology. 8th edition edition. 2007. ISBN 978-0-8089-2366-4.

References

• KUMAR, ABBAS, FAUSTO, MITCHELL,, et al. Robbins Basic Pathology. 8th edition edition. 2007. ISBN 978-0-8089-2366-4.