Microdeletion syndromes

Microdeletion syndromes are a specific group of structural chromosomal aberrations caused by deletions of a very small scale (hence the name of this group of syndromes). We classify these small-scale deletions among the so-called submicroscopic chromosomal aberrations - because during a routine karyotype examination in an optical microscope they can no longer be detected by the human eye (the theoretical limit is approx. 5 million bases ). These syndromes are also called contiguous gene syndromes or autosomal segmental aneusomy syndromes, as their clinical symptoms are caused by a failure of expression more gens. In general, these syndromes have very diverse clinical manifestations, but practically all of them have some degree of psychomotor retardation and craniofacial dysmorphia.

These small interstitial deletions arise by unequal crossing over between homologous chromosomes or unequal exchange between sister chromatids. This group of diseases also includes some syndromes associated with '''imprinting disorder, where the clinical manifestations of the deletion differ depending on whether the chromosome of maternal or paternal origin is damaged (Prader-Willi syndrome, Angelman syndrome).

When diagnosing these syndromes, it is usually not enough to carry out a routine karyotype examination, but more detailed methods must be used. When a specific syndrome is clinically suspected, it is possible to use a locus-specific FISH probe, the disadvantage is the very limited scope of such an examination (a special probe is required for each tested locus/syndrome), therefore in practice not entirely clear clinical diagnoses use rather methods that are able to test a larger number of syndromes at the same time - for example MLPA, or nowadays increasingly often microarray.

Related Articles

 * Chromosomal Abnormalities
 * Structural Chromosomal Aberration
 * Gene imprinting and human pathologies
 * Indications for karyotype examination