Lack of Correlation between Length Variation in the DNA Polymerase γ Gene CAG Repeat and Lactic Acidosis or Neuropathy during Antiretroviral Treatment

Abstract

Antiretroviral therapy, although successful in reducing HIV load and accordingly decreasing the incidence of HIV infection-related symptoms, has its drawbacks in the form of severe side effects. Recognized drug-related side effects are, for example, nausea, fatigue, lactic acidosis, neuropathy, lipodystrophy, and myopathy. Because not all patients experience these side effects, genetic factors could be involved. It is believed that the main toxicity of nucleoside analog drugs is due to a decrease in mitochondrial function, possibly by inhibition of mitochondrial DNA (mtDNA) replication. mtDNA is replicated by a multienzyme complex, the main component of which is the nuclear-encoded DNA polymerase γ. Presently, the only known variation in the DNA polymerase γ gene is variation in the number of CAG repeats in the second exon. To investigate whether CAG repeat expansion or mutations in the DNA polymerase γ (POLG) gene could predispose to peripheral neuropathy or lactic acidosis, we have sequenced part of the second exon of the DNA polymerase γ gene, containing the CAG repeat, of 59 drug-treated HIV-infected patients, 11 of whom experienced drug-induced neuropathy, and 3 of whom died from lactic acidosis. No correlation was found between numbers of CAG repeats and any of the symptoms. The coding regions of the POLG gene from the three lactic acidosis patients were then completely sequenced, but no mutations were found. In addition, no variation was detected in exons 3, 8, and 19 of seven neuropathy patients and three control subjects without symptoms. These exons were the only sites of amino acid changes between human and chimpanzee POLG genes, and were chosen as targets of tolerated variation.