Casimersen targets which exon in the DMD gene?

• A. Exon 45
• B. Exon 51
• C. Exon 53
• D. Exon 44

Answer: (C)

Casimersen is an antisense oligonucleotide designed to bind to the splice sites of exon 45 in the dystrophin gene. By masking exon 45 during RNA processing, the cell skips that exon, realigning the downstream sequence so the reading frame is restored and a shorter but functional dystrophin protein can be produced. This exon-skipping strategy is used for Duchenne muscular dystrophy patients whose mutations are amenable to skipping exon 45, offering a Becker-like dystrophin outcome rather than a complete loss. The therapy is a phosphorodiamidate morpholino oligomer (PMO) and is one of several exon-skipping treatments, each targeting a different exon (for example, some therapies target exon 51 or exon 53) depending on the patient’s specific genetic mutation.