The FDA (U.S. drug regulator) approved Scholar Rock's Isembyld to treat spinal muscular atrophy, a rare genetic disorder that causes progressive muscle weakness. The therapy is the first muscle-targeted treatment designed to improve motor function in adults and children with the condition who have already received existing therapies. Scholar Rock shares were halted in aftermarket trading after the approval. Spinal muscular atrophy affects motor neurons, the nerve cells that control voluntary muscle movement, and can impair walking, breathing and swallowing. The Muscular Dystrophy Association estimates that roughly 10,000 children and adults in the United States are affected.