Penn Study Describes First Proof of Principle for Treating Rare Bone Disease

PHILADELPHIA - Scientists at Penn’s Perelman School of Medicine Center for Research in FOP and Related Disorders have developed a new genetic approach to specifically block the damaged copy of the gene for a rare bone disease, while leaving the normal copy untouched.

Lead author Josef Kaplan, PhD, postdoctoral fellow; and senior authors Eileen M. Shore, PhD, and Frederick S. Kaplan, MD, both from the Department of Orthopaedic Surgery, published this new proof-of-principle approach for treating the disease, called FOP, in the online edition of Gene Therapy.

FOP, fibrodysplasia ossificans progressiva, is a rare genetic disorder of progressive extra bone formation for which there is presently no cure. It is caused by a mutation in the gene for ACVR1/ALK2, a bone morphogenetic protein (BMP) receptor that occurs in all classically affected individuals. Individuals who have FOP harbor one normal copy and one damaged copy of the ACVR1/ALK2 gene in each cell. The mutation increases the amount of BMP in cells to greater than normal levels, which initiates the transformation of muscles and cartilage into a disabling second skeleton of bone.

Using a special type of RNA molecule engineered to specifically silence the damaged copy of the gene rather than the normal copy -- a process known as RNA interference, or RNAi -- the scientists restored the cellular function caused by the FOP mutation by ridding cells of the mutant ACVR1/ALK2 mRNA. Cells were essentially left with only normal copies of ACVR1/ALK2 mRNA, thus adjusting the protein’s activity to normal, similar to that of cells without the FOP mutation.

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