Very small chromosomal changes, or imbalances, known as chromosome microdeletions or microduplications can be the cause of newborn birth defects, development delay and mental retardation; see Newborn birth defects and chromosome abnormalities.

Microarray Comparative Genomic Hybridisation (CGH):

Microarray CGH is a new and powerful high-resolution test that can detect imbalances of chromosomes in much finer detail than achievable by conventional chromosome testing. A comprehensive high-resolution test for small chromosomal imbalances (microduplications or microdeletions) can now be performed in a single test. Microarray CGH works by comparing the levels of patient DNA to levels of a control (normal) DNA sample, see figure below.

Patient DNA and Control DNA are coloured green and red, mixed together, and then placed onto a microarray slide, which contains spots of human genes for analysis. The microarray is analysed and the relative colour change (green and red) of the spots is measured to determine chromosomal imbalance. If a spot shows the same amount of green and red DNA then there is no chromosome imbalance. A duplication is shown by a greener spot. In contrast, a deletion is shown by a redder spot.

A 5-10mL sample of venous blood, from which we extract DNA, is needed to perform this test.

 

This image shows patient (green) and control (red) DNA that is mixed and placed on to the microarray slide. Analysis of the relative amounts of patient (green) and control (red) DNA shows whether there is a chromosome duplication or deletion.

 

Studies have shown that in patients with congenital birth defects, development delay and/or mental retardation, small microdeletion or microduplication imbalances have been found in up to 25% of cases using microarray CGH testing.

For more information see microarray CGH testing.