Resistance mutations

Drug resistance is caused by changes in the genetic material of HIV. Just as the human body is based on the genetic code in its DNA, HIV is based on the genetic code in its RNA. Random changes (mutations) in these genes cause changes in the resultant virus and some mutations lead to drug resistance.

HIV uses complex proteins, called enzymes, as a 'toolkit' with which to operate. A viral gene is actually a set of instructions for building a particular enzyme.

The gene is a long chain of RNA laid out like a string of beads, in which each 'bead' (called a codon and made up of three nucleotides) describes the amino acid that follows in the enzyme-building sequence. Each enzyme (for example, reverse transcriptase) is a specific sequence of amino acids. There are twenty different amino acids, each referred to by a single-letter code.

Just one amino acid change can alter the resulting shape of the completed enzyme. This physical and chemical property change can block an ARV drug from binding to the correct viral enzyme. Drug resistance occurs over time when an ARV can no longer bind to the virus because of its mutations.

Resistance mutations are referred to by a number which identifies the codon, that is, the position along the gene where the mutation has taken place. The number often has letters before and/or after it; e.g., M184V. The first letter refers to the amino acid found in non-mutated or 'wild-type' HIV. The second letter refers to the new amino acid that is inserted by the mutant HIV. The first letter is sometimes omitted (e.g. 41L).

M184V is a mutation in the reverse transcriptase (RT) gene that causes resistance to 3TC (lamivudine, Epivir). It is caused by a mutation at codon number 184 in the RT gene. This mutation means that an amino acid called methionine (M) is replaced by valine (V) in the RT enzyme. Virus with the M184 mutation is able to replicate despite the presence of 3TC.

Community Consensus Statement on Access to HIV Treatment and its Use for Prevention

Together, we can make it happen

We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.