This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Spinal muscular atrophy type 2 (SMA2) is a genetic neuromuscular disorder that affects the nerve cells that control voluntary muscles (motor neurons). Without treatment, progressive muscle weakness develops in babies with SMA2 between ages 6 and 12 months. Babies with SMA2 can sit without support, however, they cannot stand or walk independently. Feeding and breathing problems also develop. SMA2 is caused by changes (pathogenic variants also called mutations) in the SMN1 gene and is inherited in an autosomal recessive manner.
Diagnosis of SMA2 is suspected by symptoms and confirmed by genetic testing. SMA has been added to the list of recommended newborn screening tests in the United States, so that it can be detected prior to symptoms developing. This occurred because treatments are being developed that are changing the course of the disease. In December 2016, nusinersen (Spinraza) became the first FDA approved treatment for SMA2. Continued treatment with nusinersen is allowing many babies and children with SMA2 to reach and maintain age appropriate developmental milestones, including sitting, crawling, and walking. Breathing problems, nutrition problems, and hospital admissions also decrease in general. However, response to treatment does vary. Some children with SMA2 may not respond to the nusinersen at all or may have medical complications that prevent use of the treatment. Other treatments remain supportive.
For more information, visit GARD.