Early efforts to examine genomic changes in the clinical setting
relied on cytogenetic techniques such as chromosome karyotyping,
a widely used approach to examine chromosomes and identify
changes that could be responsible for a specific phenotype. This
technique is sometimes inadequate, however, due to its crude
limit of resolution, five to ten million bases, after which
chromosome changes can be difficult to detect under a
microscope. An approach that has emerged over recent years,
array-based comparative genomic hybridization, or array CGH,
allows genome-wide scans to detect chromosomal rearrangements at
a greatly improved resolution, down to hundreds of bases, or
more than one thousand-fold better than karyotyping. In array
CGH, the control or reference genome and the patient’s genome
are differentially fluorescently labeled and competitively
hybridized to several hundreds or thousands of DNA targets. “The
high resolution has become a very powerful aspect of this
technology, and many times when we cannot