title: HIV-1 mutational pathways under multidrug therapy.
abstract: BACKGROUND
  Genotype-derived drug resistance profiles are a valuable asset in HIV-1 therapy decisions. Therapy decisions could be further improved, both in terms of predicting length of current therapy success and in preserving followup therapy options, through better knowledge of mutational pathways- here defined as specific locations on the viral genome which, when mutant, alter the risk that additional specific mutations arise. We limit the search to locations in the reverse transcriptase region of the HIV-1 genome which host resistance mutations to nucleoside (NRTI) and non-nucleoside (NNRTI) reverse transcriptase inhibitors (as listed in the 2008 International AIDS Society report), or which were mutant at therapy start in 5% or more of the therapies studied.
  
  
  METHODS
  A Cox proportional hazards model was fit to each location with the hazard of a mutation at that location during therapy proportional to the presence/absence of mutations at the remaining locations at therapy start. A pathway from preexisting to occurring mutation was indicated if the covariate was both selected as important via smoothly clipped absolute deviation (a form of regularized regression) and had a small p-value. The Cox model also allowed controlling for non-genetic parameters and potential nuisance factors such as viral resistance and number of previous therapies. Results were based on 1981 therapies given to 1495 distinct patients drawn from the EuResist database.
  
  
  RESULTS
  The strongest influence on the hazard of developing NRTI resistance was having more than four previous therapies, not any one existing resistance mutation. Known NRTI resistance pathways were shown, and previously speculated inhibition between the thymidine analog pathways was evidenced. Evidence was found for a number of specific pathways between NRTI and NNRTI resistance sites. A number of common mutations were shown to increase the hazard of developing both NRTI and NNRTI resistance. Viral resistance to the therapy compounds did not materially effect the hazard of mutation in our model.
  
  
  CONCLUSIONS
  The accuracy of therapy outcome prediction tools may be increased by including the number of previous treatments, and by considering locations in the HIV genome which increase the hazard of developing resistance mutations.
authors.affiliation: Department of Computational Biology, Max Planck Institute for Informatics, Saarbrücken, Germany. lawyer@mpi-inf.mpg.de.
authors.forename: Glenn
authors.initials: G
authors.lastname: Lawyer
authors.forename: André
authors.initials: A
authors.lastname: Altmann
authors.forename: Alexander
authors.initials: A
authors.lastname: Thielen
authors.forename: Maurizio
authors.initials: M
authors.lastname: Zazzi
authors.forename: Anders
authors.initials: A
authors.lastname: Sönnerborg
authors.forename: Thomas
authors.initials: T
authors.lastname: Lengauer