Microdeletions and Microduplication Syndromes (Overview)
Dipl.-Biol. Uwe Heinrich, Dr. med. Imma Rost
With the introduction of high-resolution technologies as well as fluorescence in-situ hybridization (FISH), it could be proven that a growing number of clinical syndromes result from what is known as microdeletions. Microdeletion syndromes frequently lead to complex but clinically definable phenotypes. They usually occur sporadically, as individual cases within families. Most of the chromosomal microdeletion syndromes, which are caused by a lack of usually submicroscopically small chromosome sections, are accompanied by intellectual disability. However, other signs such as typical combinations of malformations and/or dysmorphic features and sometimes characteristic “behavioural phenotypes” are almost always paramount. In these cases, there is usually a tentative diagnosis, which requires a specific analysis. Some of the microdeletion syndromes are among the more frequently occurring genetic disorders, primarily the microdeletion 22q11.2, which, amongst others, causes the DiGeorge syndrome and occurs with a frequency of approx. 1:4,000. Another frequently used term for microdeletion syndromes is contiguous gene syndromes, since the signs and symptoms are thought to be caused by the lack of several genes located in the region of deletion.
The following table (classic microdeletion syndromes) provides an overview over some major microdeletion syndromes which are part of routine diagnostics. Some of the mentioned syndromes may also have other causes (single gene mutations e.g. in AS and/or UPD e.g. in PWS and AS).
The use of array CGH has defined numerous new microdeletion and microduplication syndromes (see table) which were entirely unknown a few years ago and whose phenotypes were sometimes recognized as characteristic only after repeated description of the same imbalance.