What defines primary resistance mutations in HIV?

Primary resistance mutations in HIV refer specifically to genetic changes in the virus that reduce its susceptibility to particular antiretroviral drugs. These mutations typically arise in patients who have not previously been exposed to antiretroviral therapy and are characteristic of specific classes of medications.

When HIV mutates through these primary resistance mechanisms, it alters the structure of viral proteins, which in turn affects how the drugs interact with the virus. This means that when a patient begins treatment with a specific drug, the presence of these mutations can lead to treatment failure because the virus is inherently less susceptible to the effects of that drug.

In contrast, other options do not accurately describe primary resistance mutations. For instance, mutations that do not affect drug susceptibility cannot be classified as resistance mutations, and those that appear after prolonged therapy are often categorized as secondary or acquired mutations, not primary. Additionally, primary resistance mutations are not common across all strains of HIV; they are typically specific to certain strains or subtypes and particular drugs. Therefore, the correct explanation focuses on the direct relationship between these mutations and their effect on drug effectiveness.