NEW YORK (AP) — Shares of Insmed Corp. plunged Thursday after the company said its drug Iplex failed to treat the most common form of muscular dystrophy in a midstage study. Shares of Insmed fell $1.24, or 54 percent to $1.09 in morning trading. The stock has traded between 32 cents and $2.57 over the last 52 weeks. The drug is already approved to treat a growth hormone deficiency. In the study, Iplex did not improve endurance, muscle function, or muscle strength. Symptoms of myotonic muscular dystrophy include the deterioration of muscle throughout the body. There were 69 patients enrolled in the study. The company said the study was only “exploratory” and therefore had no predefined goals. Insmed said it intends to apply for a grant from the Muscular Dystrophy Association to conduct an additional Phase II trial focused solely on a subset of patients with severe insulin resistance who, based on results of the study, may be more likely to benefit from Iplex.