Adeno-associated viral (AAV)
Adeno-associated viral (AAV) is a small, non-disease causing virus that can infect both dividing and non-dividing human cells. AAV cannot replicate on its own and is non-pathogenic. The AAV used for gene therapy does not insert DNA into the genome, but does deliver DNA to the host cell nucleus. Consequently, AAV vector can be used as an efficient delivery vehicle for the long-term expression of therapeutic proteins in humans. However, because of its small size, AAV cannot be used to deliver a full length dystrophin gene or express full-length dystrophin protein. AAV is currently being utilized to deliver shortened mini/micro-dystrophin genetic sequences that will lead to expression of mini/micro-dystrophin protein in muscles throughout the body in DMD patients.
Anti-fibrotic therapy: Fibrosis is a hallmark of chronic inflammation and muscle degeneration in DMD. An anti-fibrotic drug targets those mechanisms associated with the fibrotic process and aims to inhibit, reduce or remodel fibrosis. By reducing scar formation, anti-fibrotic therapies may not only improve muscle function but also enhance muscle regeneration and promote gene and stem cell engraftment.
Anti-inflammatory therapy refers to the property of a substance or treatment that reduces inflammation or swelling by targeting known and novel inflammatory mechanisms. Chronic inflammation leads to fibrosis and reduced muscle regeneration.
Antisense oligonucleotides are short strands of deoxyribonucleotide analogue that hybridize with their complementary mRNA target in a sequence-specific manner. In DMD, this mechanism is typically employed to target pre-mRNA to manipulate the splicing pattern so that an out-of-frame mutation becomes an in-frame mutation capable of producing a novel dystrophin protein.
Cardiac failure is the leading cause of death with those of Duchenne. DMD-associated dilated cardiomyopathy is a form of cardiac failure that is caused by mutations in the DMD gene. Dilated cardiomyopathy enlarges and weakens the cardiac muscle, preventing the heart from pumping blood efficiently.
CRISPR-Cas9 is a nuclease (enzyme that cuts DNA) found in bacterial cells. In nature, CRISPR-Cas9 operates as part of a primitive immune system that prevents infection. However, when coupled with specific guide-strand RNA sequences, CRISPR-Cas9 can be used as a targeted genome editing tool that can be used to efficiently edit DNA within mammalian cells. Two components are necessary for the system to work: a small RNA guide sequence that directs the Cas9 to a specific DNA sequence where the cut is to be made, and a Cas9 enzyme that snips through DNA like a pair of scissors. Once a cut has been made, the cell’s own DNA repair machinery will rejoin the fragmented ends to restore a continuous DNA sequence. This technology has the potential to permanently correct the faulty DNA present in a Duchenne patient.
Duplication is a DNA segment in a chromosome that is a copy of another segment.
Duchenne muscular dystrophy
Duchenne muscular dystrophy is a fatal, progressive, X-linked recessive genetic disease that causes muscle degeneration and weakness. It results from mutations in the gene responsible for producing the key muscle protein dystrophin. The disease occurs in approximately 1:5000 boys born worldwide. Most patients are diagnosed before 5 years of age, when their physical ability diverges from their peers. Untreated, muscle strength deteriorates, and boys require the use of a wheelchair before their teens. Respiratory, orthopedic, and cardiac complications emerge in late teens.
DMD gene is one of the largest known human genes, and provides instructions for making a key muscle protein called dystrophin. This protein is located primarily in muscles used for movement (skeletal and breathing muscles) and in heart muscle.
Dystrophin is a key muscle protein, and is absent in patients with Duchenne muscular dystrophy. Dystrophin is part of a large group of proteins that work together to help support and strengthen muscle cells and fibers and protect them from injury as muscles contract and relax. The dystrophin complex acts as shock absorber, connecting each muscle cell’s internal structural framework with proteins and other molecules outside the cell.
Exon skipping is a form of RNA splicing used to cause cells to “skip” over and remove faulty or misaligned sections of genetic code called exons, leading to the production of a truncated but still functional protein. Exon skipping is a potential treatment option for specific genetic mutations on the dystrophin preRNA where it could correct the reading frame and restore the production of a shorter form of dystrophin protein.
Fibrosis is the thickening and scarring of connective tissue following injury.
Gene editing is a type of genetic engineering in which DNA is inserted, deleted or replaced in the genome of a living organism using engineered nucleases, or “molecular scissors.” Gene editing could correct mutations in the existing DNA of those with Duchenne.
Gene therapy is the introduction of new genetic material into cells to replace missing or defective proteins to correct genetic disorders. Gene therapy approaches for Duchenne typically aim to deliver new and non-native micro-/mini-dystrophin DNA sequences.
Gene correction is a technology that gives us the tools for both repairing and mutating DNA, for discovering gene functions and for engineering new genetic variants.
Muscle regeneration is the process by which damaged skeletal, smooth or cardiac muscle undergoes biological repair and formation of new muscle in response to death of muscle cells.
Mutation is the changing of the sequence of a gene. This results in a variant form of the gene that may (or may not) be transmitted to subsequent generations, and is caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.
Myostatin is a protein produced mainly in muscle that inhibit muscle generation. Inhibition of myostatin offers a novel therapeutic approach to the regeneration of new muscle.
Nonsense mutation is a point mutation in a sequence of DNA that results in the production of a premature stop codon, or a nonsense codon in the transcribed mRNA. This leads to a truncated, incomplete, and usually nonfunctional protein.
Stop-codons are natural sequences found in DNA and RNA that are required to terminate protein translation from mRNA.
Utrophin upregulation is a promising pharmacological treatment for Duchenne that aims to increase levels of utrophin, a homologue of dystrophin, in muscle fibers of affected patients to compensate for the absence of dystrophin.