Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a group of neuromuscular disorders that result in the loss of motor neurons and progressive muscle wasting. The severity of symptoms and age of onset varies by the type. Some types are apparent at or before birth while others are not apparent until adulthood. All generally result in worsening muscle weakness associated with muscle twitching. Arm, leg and respiratory muscles are generally affected first. Associated problems may include problems with swallowing, scoliosis, and joint contractures. SMA is a leading genetic cause of death in infants. Spinal muscular atrophy is due to a genetic defect in the SMN1 gene. They are inherited from a person's parents in an autosomal recessive manner. The SMN1 gene encodes SMN, a protein necessary for survival of motor neurons. Loss of these neurons prevents the sending of signals between the brain and skeletal muscles. Diagnosis is suspected based on symptoms and confirmed by genetic testing. Treatments include supportive care such as physical therapy, nutrition support, and mechanical ventilation. The medication nusinersen, which is injected around the spinal cord, slows the progression of the disease and improves muscle function. In 2019, the gene therapy onasemnogene abeparvovec was approved in the US as a treatment for children under 24 months. Outcomes vary by type from a life expectancy of a few months to mild muscle weakness with a normal life expectancy. The condition affects about 1 in 10,000 people at birth.