CARLSBAD, Calif., Nov. 1, 2012 /PRNewswire/ -- Isis Pharmaceuticals, Inc. (NASDAQ: ISIS) announced the initiation of a Phase 1b/2a study evaluating ISIS-SMNRx in children with spinal muscular atrophy (SMA). SMA is a severe and rare genetic neuromuscular disease characterized by muscle atrophy and weakness and is the most common genetic cause of infant mortality. "SMA is a devastating disease that leads to the premature loss of nerve cells in the spinal cord necessary for normal muscle function. Children with SMA generally appear normal at birth, with muscle wasting and atrophy developing as early as a few months after birth. In the most severe form of the disease, children never sit or walk and have a significantly shortened lifespan. Although the genetic cause of SMA is well understood, the identification of an effective drug that will halt or improve the disease process has not occurred," said Richard Finkel, M.D., chief, division of neurology, Nemours Children's Hospital, Orlando, Florida. "ISIS-SMNRx is specifically designed to intervene in the nerve cell's RNA machinery by improving splicing efficiency. This results in an increase in the production of a normal protein, SMN, which is deficient in children with SMA. This promising new approach could for the first time have a profound effect in children with SMA." The Phase 1b/2a study of ISIS-SMNRx is a multiple-dose, dose-escalation study designed to assess the safety, tolerability and pharmacokinetic profile of the drug in children with SMA between the ages of 2-15 who are medically stable. In the ongoing Phase 1 study in children with SMA, all patients have completed dosing and ISIS-SMNRx was well tolerated as a single dose administered directly into the cerebral spinal fluid. In the Phase 1b/2a study, children with SMA will receive either two or three doses of ISIS-SMNRx during the course of the study. Data from this study will also provide information to aid in identifying the dose for the Phase 2/3 registration-directed program in patients with SMA.