CGH ARRAY STUDY:

Recent development of array-CGH has shown that, it is possible to substitute the chromosome target by a DNA spot on a glass slide. The processing technique is similar to that of CGH metaphase, a mixer of equal quantities of DNA from the patient and control is labelled with different fluorochromes is used and hybridized on a coated glass slide where an ordered set of defined nucleic acid sequences are spotted. This technological development allows screening of large number of genomic DNA sequences in a single experiment, depending on the size of the spot. Chromosomal imbalances across the genome can be mapped and quantified by analyzing the fluorescence ratio of the two dyes for each target. DNA quantitative variation can be identified, only if the DNA fragments used on the glass slide covers regions of interest.

Conventional cytogenetic is a gold standard for the detection of genetic alterations in constitutional and acquired anomalies. 400-bands karyotype allows detection of anomalies up to 10-15 Mb whereas high resolution helps in revealing between 3-5 Mb. Developments of more accurate technique - FISH has helped us in identifying various micro-deletions and sub-telomeric exchanges even in non-dividing cells. Introduction of array-CGH has brought much higher resolution to detect the genomic imbalances. BAC/PAC or oligonucleotide based array-CGH is useful in the detection of quantitative imbalance of constitutional, haematological and solid tumor as well. The resolution varies from several kb to 1 Mb depending upon the type of array selected. More recent improvement in the array-CGH technology will definitely make a link between cytogenetic and molecular biology despite of Copy Number Variations/ Polymorphisms and without replacing conventional cytogenetic. This technology will prove to be more and more helpful in the diagnosis of quantitative cryptic imbalances of whole genome in the near future.

A case of trisomy 18p detected by CGH array