Spinal muscular atrophy (SMA) is a genetic, neuromuscular disorder caused by progressive degeneration of motor neurons in the spinal cord, which results from the loss of survival motor neuron (SMN) protein. The disorder is characterized by weakness and wasting of the voluntary muscles and is a leading cause of hereditary infant death. Sodium phenylbutyrate—a drug used to treat urea cycle disorders—may increase the amount of SMN protein in the body and consequently may decrease the severity of SMA. However, this has not yet been proven.