Final answer:
Variation in the NAT2 gene affects the metabolic activation of isoniazid, used to treat TB, and can lead to failure of a once weekly dose for some patients.
Step-by-step explanation:
Variation in which gene is associated with failure of a once weekly dose of isoniazid for tuberculosis treatment? The answer is D NAT2. Isoniazid, a prodrug used in the treatment of tuberculosis (TB), requires metabolic activation. This activation is influenced by genetic variations in enzymes that metabolize drugs. Pharmacogenomics is the study of how these genetic variations affect an individual's response to therapeutic drugs. One particular enzyme, encoded by the NAT2 gene, is responsible for the acetylation of isoniazid. Variations in this gene can lead to slow acetylation rates, meaning that standard doses may not be effective for individuals with these variants, potentially requiring dosage adjustments to achieve therapeutic effectiveness and to prevent the emergence of drug resistance.