Some 220 professionals — physicians associated with MDA who treat patients with neuromuscular diseases, and MDA-supported scientists conducting research on these conditions — gathered in Tucson, Ariz., Nov. 17 through Nov. 19 for Translating Basic Research Into Clinical Strategies.
MDA, the University of Arizona College of Medicine and Arizona Health Sciences Center sponsored the conference, which was chaired by neurologist Jerry Mendell of Ohio State University and Columbus (Ohio) Children’s Research Institute, and biochemist Kevin Campbell at the University of Iowa, both longtime MDA grantees.
|Steven Wilton described how cells can be coaxed into ignoring parts of a genetic message that contain mutations.|
|H. Lee Sweeney's work helped lay the foundation for PTC124, which targets erroneous stop signals in the dystrophin gene.|
|Jeffrey Chamberlain showed the audience how mice with muscular dystrophy were improved by highly miniaturized dystrophin genes.|
|Donald Sanders described MuSK-related MG.|
Duchenne MD: gene rereading, gene transfer
Among the conference’s highlights were several demonstrations of how careful study of the gene for dystrophin, the protein missing in boys with Duchenne muscular dystrophy (DMD), has resulted in strategies for treating the disease.
Steven Wilton, an MDA grantee at the University of Western Australia in Perth, described a technique called exon skipping for the treatment of DMD. Wilton’s strategy, made possible by years of MDA-supported study of the gene for dystrophin, takes advantage of the way dystrophin DNA, after being converted to RNA, is processed, prior to synthesis of the dystrophin protein.
Exons, the parts of an RNA strand that are reflected in the final structure of the protein, are interrupted by introns, which are removed from the RNA by the cell’s processing mechanisms. Wilton and colleagues have developed a method for coaxing cells to ignore exons containing genetic errors (mutations) and to splice together exons on either side of them, thereby allowing a nearly normal dystrophin protein to be made.
MDA grantee H. Lee Sweeney, from the University of Pennsylvania, described another molecular strategy for the treatment of DMD, which is further along in the drug development pipeline. In this approach, called stop codon read-through, cells are encouraged to ignore erroneous (premature) stop signals in the dystrophin gene thought to cause DMD in approximately 15 percent of boys with the disease. These premature stop signals cause a shortened and nonfunctional protein to be made.
PTC Therapeutics, a biotech company in South Plainfield, N.J., with support from MDA and basic science contributions from Sweeney, has developed an experimental drug called PTC124 that’s slated for testing in boys with DMD this year. It has already been tested and found safe in healthy volunteers.
Identification of boys with premature stop signals in the dystrophin gene has been made possible by meticulous study of the gene and development of new methods for pinpointing each patient’s precise mutation. Kevin Flanigan, from the University of Utah in Salt Lake City, described his laboratory’s method for such precise diagnosis by complete sequencing of the dystrophin gene.
University of Washington-Seattle biologist Jeffrey Chamberlain, a longtime MDA grantee, showed how mice missing both dystrophin and a closely related compound, utrophin, and therefore showing severe MD symptoms, were helped by a single injection of highly miniaturized dystrophin genes into the bloodstream at 1 month of age.
Chamberlain’s group learned how to make the miniaturized (microdystrophin) genes after years of study to determine which parts of the very large dystrophin gene were essential and which could be eliminated. The microdystrophin genes they created fit into a highly effective and apparently safe adeno-associated virus (AAV) delivery vehicle. These mice were injected with microdystrophin genes inside type 6 AAV shells.
Mitochondrial Disease: working from within
Eric Schon, a molecular biologist at Columbia University in New York, thanked MDA for support over the years to his study of mitochondria, the miniature organs inside cells that produce most of the cells’ energy. When things go wrong in these miniorgans (organelles), as happens in the mitochondrial myopathies, adverse effects on the muscles and nervous system can be severe.
Schon explained that mitochondria have their own DNA but also rely on DNA from the cell nucleus to carry out their functions.
|Deya Corzo (left), a physician with Genzyme Corp., talks with Kevin Kimata, co-director of the MDA clinic in Honolulu.|
|Valerie Cwik (left), a neurologist and MDA's medical director, talks with Ann Henderson Tilton, who co-directs the MDA clinic at Children's Hospital in New Orleans.|
In Schon’s laboratory, potentially therapeutic DNA can be inserted into a cell nucleus with a tag that tells the cell to send the newly made protein to the mitochondria. His lab group has also attacked mutations in mitochondrial DNA by inserting a highly targeted DNA-cutting enzyme that snips out a mitochondrial DNA mutation and leaves intact the surrounding, normal DNA.
Disorders of nerve-to-muscle signal transmission, known as myasthenias, can be either acquired or genetic.
Donald Sanders, who co-directs the MDA clinic at Duke University Medical Center, described how basic science research that increased understanding of MuSK, a protein on the muscle side of the nerve-to-muscle (neuromuscular) junction, led physicians to recognize a new type of myasthenia gravis (MG), in which the immune system attacks this protein.
In the more common type of MG, the immune system attacks the acetylcholine receptors, “landing pads”on muscle cells where nerve signals are received.
C. Michel Harper, who works with longtime MDA grantee Andrew Engel at the Mayo Clinic in Rochester, Minn., described how basic research on the neuromuscular junction has resulted in the understanding of how genetic mutations affect the way acetylcholine, a signal-transmitting chemical, is packaged, transmitted, received or broken down.
Defects in these processes can lead to distinct congenital myasthenic syndromes, each of which requires a treatment tailored to the underlying molecular defect.