Question

how have genetic studies helped explain why two cf patients with the exact same mutated allele and healthy lifestyle may have completely different medical outcomes?

• patients with a second mutation on chromosome 19 have a better immune response and heal faster after cf episodes.
• some patients have a second mutation, such as a tgfb1 allele mutation, which generates more scarring after lung infections.
• outcome depends upon which cftr gene is affected by the mutation.
• some patients respond differently to medications than others.

Explanation:

In genetic studies, it's known that modifier genes can influence the phenotype of a primary mutation. Cystic fibrosis (CF) is mainly caused by mutations in the CFTR gene. However, other genes (like TGFB1 - transforming growth factor beta 1) can act as modifiers. A TGFB1 allele mutation can lead to differences in the extent of scarring (fibrosis) after lung infections (a common complication in CF). This scarring can significantly impact the long - term lung function and overall medical outcome of CF patients.

• Option A: There is no evidence that a second mutation on chromosome 19 (in general, without specifying a gene like TGFB1) leads to a better immune response.
• Option C: The question states that the patients have the exact same mutated allele (implying the same CFTR gene mutation), so this option is incorrect.
• Option D: While medication response can vary, the question specifically asks about genetic studies explaining the difference, and this option is more about pharmacology (response to drugs) rather than a genetic modifier (like TGFB1) as the main genetic - based explanation.

Answer:

B. Some patients have a second mutation, such as a TGFB1 allele mutation, which generates more scarring after lung infections.