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Genotypic vs. phenotypic

May 22, 2004

Big question, but I was wondering your opinion. What are the advantages and disadvantages to phenotypic resistance testing and genotypic and what's a virtual phenotype? What do you use and why?


Response from Dr. Holodniy

These are difficult and complicated questions that are debated by many experts, and published studies are conflicting as to whether there is an advantage of one technology over another.

I have used all 3 technoliges in clinical practice. Genotyping is cheaper, faster, but not for the faint hearted, as it requires an understanding of the clinical significance of various mutations and their interactions.

Phenotyping is more expensive, takes longer, but provides relevant information as to how a particular patient's virus grows in the presence of each HIV drug.

A virutual phenotype is where a patients virus sequence is matched to a large database where many viruses have been sequenced and have had phenotypes performed. A probabilistic estimate of drug resistance or susceptibility is given based on the number of matches in the database. It is only slightly more expensive than genotyping, and appears equal to phenotyping in randomized trials, in terms of virologic outcome.

I am unphenotypable. Why and how common is this?
Genotypic test questions

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