Duchenne Muscular dystrophy (DMD) can be caused by a mutation leading to the exclusion of exons 49 and 50 of the dystrophin gene (exon pattern illustrated below). 

Which of the following proposed antisense oligonucleotide (ASO) treatment would likely be most effective for patients with this mutation, to allow them to produce some functional dystrophin protein?

A 7-year-old patient is diagnosed with a rare inherited

disorder caused by mutations in a gene too large to fit into a single

adeno-associated virus (AAV) vector. Researchers are designing a gene therapy

approach that splits the therapeutic gene into multiple segments and relies on

inteins to reassemble the full-length protein inside target cells.

Why are inteins particularly useful in this therapeutic

context?

A

40-year-old individual with well-controlled HIV enrols in a study testing a

genome-editing approach to reduce viral susceptibility by disrupting the CCR5

co-receptor in their CD4+ T cells. Investigators must choose a delivery method

that maximizes editing efficiency while minimizing systemic exposure and

insertional risks.

Which

delivery approach BEST aligns with the established strategy for CCR5-directed

ZFN therapies?

Researchers are developing a CRISPR–Cas9 therapy to correct

a pathogenic point mutation in a gene responsible for an inherited blood

disorder. During preclinical testing, several unintended genomic regions are

also cleaved, raising concerns about off-target effects. The research team

decides to redesign part of the CRISPR system to improve targeting precision.

Which component of the CRISPR–Cas9 system would most

directly need to be modified to improve DNA targeting specificity, and why?

Researchers aim to silence a disease-causing allele that

produces a toxic protein by introducing a site-specific double-strand break in

the gene. No donor DNA is supplied, as the goal is to disrupt gene function

rather than repair it.

Which DNA repair mechanism is intentionally relied upon in

this approach, and what makes it suitable for this purpose?

A couple seeks reproductive counselling after genetic

testing reveals that the prospective mother carries a mutation in her

mitochondrial genome associated with a fatal childhood disorder. They wish to

reduce the risk of passing this condition to their child while retaining a

genetic link to both parents.

Which outcome best describes the intended role of

mitochondrial replacement therapy in this situation?

A patient receives an experimental gene therapy to treat an

inherited neurological disorder. Several years later, follow-up imaging and

biopsies show persistent expression of the therapeutic protein, with no

evidence of oncogenic transformation or disruption of host gene function in

treated cells.

Which property of the viral vector used in this therapy most

likely contributed to this favourable long-term safety outcome?

A researcher is designing a zinc finger nuclease (ZFN) to

selectively disrupt a disease-causing gene in human cells. Precise targeting is

essential to minimise off-target double-strand breaks elsewhere in the genome.

Which feature of ZFNs provides the sequence specificity

required for accurate targeting of the desired DNA locus?

A pharmaceutical company is preparing a first-in-human

clinical trial for a new small-molecule drug. Before selecting a safe starting

dose for healthy volunteers, the compound is administered to animals in a

single-dose, acute pre-clinical toxicity study to assess immediate adverse effects.

Which piece of information from this study would be most

relevant for guiding the choice of the initial human dose?

Certain mutations in the dystrophin gene disrupt the reading

frame, leading to little or no dystrophin production and the severe clinical

features seen in Duchenne muscular dystrophy (DMD). However, when the reading

frame is preserved—even if parts of the protein are missing—muscle function is

partially maintained, as observed in Becker muscular dystrophy.

How do antisense oligonucleotide therapies exploit this

difference to improve outcomes in patients with DMD?