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I am unphenotypable. Why and how common is this?
May 16, 2004

I haev been positive for 15+ years and have run through most available meds with developing resistance. I've had phenotype testing done multiple times, at different labs, and the results are always the same. My virus is "unphenotypable" which limits my doctor's ability to make informed recommendations. How common is this and what causes it? Can it be interpreted as something good (i.e. a weaker strain of virus)?

Response from Dr. Sherer

A small percent of patients with viremia are 'unphenotypable', for reasons we don't understand.

The answer you have offered may be the explanation for this uncommon phenomenon, i.e. that the virus has numerous resistance mutations which make it less 'fit', and thus unable to be subjected to the standard phenotype assays, in which your own virus is tesetd against individual ART drugs. There is some evidence that this may be a good thing, i.e. that a less fit virus is associated with a lesser risk of HIV disease progression, but we are still learning about the implications of fitness and its laboratory surrogate, 'replication capacity'.

I advise you to talk this through with your doctor. In my opinion, the information obtained from a genotype provides very useful information on which to base treatment decisions in the absence of a phenotype.

Undetectable, yet falling CD-4 count?
Genotypic vs. phenotypic tests

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