Fluorescentie-in-situhybridisatie bij het onderzoek naar chromosomale afwijkingen

- Classical cytogenetics has a low resolving power and allows analysis of dividing cells only.

- In fluorescence in situ hybridization (FISH), a DNA fragment is stained with a fluorescent marker, after which this fragment is brought into contact with a patient's DNA. The stained fragment can bind to a corresponding fragment, revealing its presence or absence.

- Using FISH, every desired DNA sequence (from a whole chromosome to one gene) can be stained. In this way it is also possible to diagnose microdeletion syndromes, such as the Williams syndrome, the DiGeorge syndrome and submicroscopial chromosome anomalies that play a part in mental handicaps.

- FISH also allows analysis of non-dividing cells. In this way it is possible for instance rapidly to examine uncultured amniotic fluid cells for the commoner trisomies or to find foetal erythrocytes in a pregnant woman's blood. It is also possible to demonstrate tumour-specific breaking points.

- By application of FISH to microarrays it is possible to study a large number of genes simultaneously for the presence of a particular number of DNA sequences linked to a clinical abnormality.