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Update on the Diagnosis and Monitoring of HIV-1 Infection
Genotype assays are used more commonly than phenotypic assays because changes. All of the standard genotyping assays listed above are limited in
they are easier to run, cost-effective, and have faster turnaround times. In their ability to detect emerging resistance in mixed viral populations. The
addition, they detect mutations before they are phenotypically expressed. lower limit of detection of mixed mutations in most of these assays is in the
However, accurate interpretation relies on the analyst’s knowledge of 20–25% range. Several research methods, such as the Oligo-Ligase assay
complex mutations and mutational interactions. Moreover, mutations are (OLA), Ty-1 HIV-RT assay, and Single Genome Sequencing (SGS) assay, are
not always consistent with the results derived from phenotypic assays. currently employed in clinical trials. These assays are capable of detecting
Currently, several types of genotypic and phenotypic assays exist for testing. emerging resistance mutations in the 2–5% range.
The TruGene™ HIV-1 genotyping kit and OpenGene DNA sequencing system powerful genotypic way of determining HIV-1 drug resistance is the use of
(Visible Genetics/Bayer Diagnostics) and ViroSeq™ HIV-1 Genotyping microarray technology. Affymetrix Inc. has developed specific DNA chips
systems with the 3700 Genetic Analyzer (Celera Diagnostics/Applied that can be used to detect all the possible gene mutations conferring drug
Biosystems/Abbott Laboratories) are FDA-approved. Both offer an integrated resistance to either RT or PR inhibitors. Although rapid, this test is limited by
software algorithm to give the clinician information about which gene its high cost and instrument set-up.
mutations of RT and PR are most likely to confer resistance to a specific drug
regimen. Another method, the INNO-LiPATM HIV-1 RT assay Conclusion
(Innogenetics/Bayer Diagnostics), is a reverse hybridization method that uses The development of tests such as microarray chips, PCR tests, and rapid
easy-to-read strips to determine specific viral gene codon changes that tests attests to the great advances that have been made in HIV diagnostics,
confer drug resistance. However, the test identifies only the gene mutations and provide hope for better and faster detection and monitoring of HIV.
that have been targeted by certain oligonucleotides applied on the strip. The goal is to keep ahead of a rapidly changing virus. With the aid of
Another method that uses the DNA repair enzyme Cleavase™ in the recent changes in screening, surveillance, and mandatory testing
Invader™ assay (Third Wave) could potentially detect all viral gene recommendations, management of HIV may be able to keep up with the
mutations, but is unable to provide specific information on gene codon ever-mutating virus. ■
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