In this example of gene therapy, the treatment is successful if the A - VCE - SSCE Biology - Question 9 - 2012 - Paper 1

In gene therapy, simply inserting the normal allele into the nuclear DNA of airway cells (option A) is not sufficient; the expression of that allele is critical for the therapy's effectiveness. If the normal allele is expressed, it produces the necessary functional protein that may compensate for the defective gene. Furthermore, while reducing inflammation (option B) and ensuring particle entry (option D) are important considerations in therapy design, they do not guarantee the treatment's success on their own. Thus, effective expression of the allele is the key determinant in the success of gene therapy.