Injection of double-stranded RNA can lead to gene silencing by degradation of RNA molecules complementary to either strand of the dsRNA. Could RNAi be used in gene therapy for a defect caused by a recessive allele? A dominant allele? If so, what might be the major obstacle to using RNAi as a therapeutic agent?

Verified step by step guidance

1. Step 1: Understand the mechanism of RNA interference (RNAi). RNAi involves the introduction of double-stranded RNA (dsRNA) that is complementary to a target mRNA, leading to its degradation and thus silencing the expression of that gene. This process can reduce or eliminate the production of the protein encoded by the target gene.
2. Step 2: Consider the application of RNAi in gene therapy for a recessive allele defect. Since recessive disorders typically result from loss-of-function mutations, the defective allele usually produces little or no functional protein. RNAi, which silences gene expression, would not be beneficial here because the problem is insufficient protein rather than excess or harmful protein.
3. Step 3: Consider the application of RNAi in gene therapy for a dominant allele defect. Dominant disorders often arise from gain-of-function mutations or dominant-negative effects, where the mutant allele produces a harmful protein. RNAi could be used to selectively silence the mutant allele's mRNA, reducing the harmful protein's production and potentially alleviating disease symptoms.
4. Step 4: Identify the major obstacle in using RNAi therapeutically. One key challenge is achieving allele-specific silencing—RNAi must target only the mutant allele without affecting the normal allele to avoid unwanted side effects. Designing RNAi molecules that discriminate between alleles differing by only a single nucleotide can be difficult.
5. Step 5: Consider additional obstacles such as delivery methods, stability of RNAi molecules in the body, off-target effects, and immune responses. Efficient and safe delivery to the correct cells and tissues is critical for successful RNAi-based gene therapy.

Key Concepts

RNA Interference (RNAi) Mechanism

RNAi is a biological process where double-stranded RNA triggers the degradation of complementary messenger RNA, effectively silencing specific genes. This mechanism can selectively reduce the expression of target genes, making it a powerful tool for regulating gene activity in research and therapy.

Genetic Basis of Recessive and Dominant Alleles

Recessive alleles cause a phenotype only when both copies are defective, while dominant alleles express their effect even if only one copy is mutated. Understanding this distinction is crucial for determining whether gene silencing via RNAi can compensate for or suppress the defective gene product.

Challenges of RNAi in Gene Therapy

Major obstacles in using RNAi therapeutically include delivery to target cells, specificity to avoid off-target effects, and ensuring sustained gene silencing without triggering immune responses. These challenges must be addressed to safely and effectively use RNAi for treating genetic disorders.