M-chip is a DNA chip designed for a high-resolution approach to detect chromosomal abnormalities in prenatal diagnosis. DNA fragments which represent the major regions of fetal genome are attached to the chip.
In a clinic, fetal cells are collected by Chorionic villus sampling (CVS) and amniocentesis.
DNA is extracted from the fetal cells, labeled with green fluorescent dye, and hybridized. Normal DNA labelled with red fluorescent dye is competitively hybridized as a control. By comparing relative fluorescence signal, numerical and structural chromosomal abnormalities are detected.
1. Technical Aspects
Chance of having a baby with chromosomal abnormalities such as Down syndrome increases with maternal age. For mothers older than 35 or classified as a high risk group after biochemical screening, chorionic villus sampling (CVS) and amniocentesis are typically performed to diagnose a problem. Karyotyping is performed to diagnose chromosomal abnormalities in metaphase by visual identification using microscopy. Some disadvantages of Karyotyping include inefficiency of visual identification using microscope, and detection inability of subtle chromosomal alterations. Cell culture and experts are also needed to be done for the karyotyping. Fluorescent In Situ Hybridization (FISH) is developed to overcome limitations of karyotyping to detect loss of chromosome or duplicated regions, but it is relatively expensive and time consuming.
M-scanning is a prenatal genetic screening assay to detect chromosomal abnormalities using both DNA chip and karyotyping.