COMPARATIVE GENOMIC HYBRIDIZATION - AN OVERVIEW

Comparative genomic hybridization (CGH) is a newly described molecular -cytogenetic assay that globally assays for chromosomal gains and loss es in a genomic complement. In this assay, normal human metaphase chro mosomes are competitively hybridized with two differentially labeled g enomic DNAs (test and reference), which upon fluorescence microscopy, reveal the chromosomal locations of copy number changes in DNA sequenc es between the two complements. Application of CGH to DNAs extracted f rom fresh frozen specimens and cell lines of various tumor types has r evealed a number of recurring chromosomal gains and losses that were u ndetected by traditional cytogenetic analysis. Few previously known si tes were found to be in higher copy number, or lost by CGH, while many novel amplified regions were identified. These regions warrant furthe r molecular genetic studies aimed at isolating the perturbed genes. Si nce CGH can also be Performed on DNA extracted from formalin-fixed par affin-embedded archived tumor specimens with few modifications, gains and losses of genetic material can be determined for specimens that wo uld otherwise be unanalyzable. Prospective and retrospective applicati on of CGH to tumor specimens would permit correlative studies to be pe rformed, possibly identifying diagnostic and prognostic indicators of disease CGH may also have a future role ill detection and identificati on of chromosomal abnormalities in prenatal diagnosis and ill dysmorph ic anomalies.