Which statement best explains why genetic differences in drug targets are less numerous than variations in drug-metabolizing enzymes?

Which statement best explains why genetic differences in drug targets are less numerous than variations in drug-metabolizing enzymes?

• A. Genetic variations in drug target sites are less numerous than metabolic enzyme variations
• B. Genetic variations in drug target sites are more numerous than metabolic enzyme variations
• C. There are no genetic variations in drug target sites
• D. Target-site genetics are irrelevant to drug response

Answer: (A)

Genetic differences in drug targets are fewer because those targets—receptors, enzymes, and ion channels—that drugs bind to are essential for normal physiology and tightly conserved. When a change occurs in a target site, it can disrupt normal signaling or essential functions, which often leads to negative effects and is selected against. In contrast, drug-metabolizing enzymes—like the CYP450 family—can vary more in activity and substrate preference without immediately harming basic survival. These enzymes encounter a wide range of dietary and environmental substances, so genetic diversity in their genes is common and can be maintained by population-level pressures. The result is greater polymorphism in metabolism, which drives much of interindividual drug exposure differences, whereas target-site variations are less common due to functional constraints. While there are some target variations that can affect response, they are relatively rare compared to metabolic enzyme variations, and target-site genetics are not irrelevant to drug response.

Genetic differences in drug targets are fewer because those targets—receptors, enzymes, and ion channels—that drugs bind to are essential for normal physiology and tightly conserved. When a change occurs in a target site, it can disrupt normal signaling or essential functions, which often leads to negative effects and is selected against. In contrast, drug-metabolizing enzymes—like the CYP450 family—can vary more in activity and substrate preference without immediately harming basic survival. These enzymes encounter a wide range of dietary and environmental substances, so genetic diversity in their genes is common and can be maintained by population-level pressures. The result is greater polymorphism in metabolism, which drives much of interindividual drug exposure differences, whereas target-site variations are less common due to functional constraints. While there are some target variations that can affect response, they are relatively rare compared to metabolic enzyme variations, and target-site genetics are not irrelevant to drug response.