Spinal muscular atrophy type 1 (SMA1), also known as Werdnig-Hoffman disease, is one type of a group of conditions known as spinal muscular atrophies (SMAs). SMAs are inherited disorders that cause a child to lose a specific type of cell in their spinal cord (motor neurons) and a part of their brain that is connected to the spinal cord (brain stem). Without these important parts of the brain and spinal cord, an affected child loses control of muscle movement, has muscle weakness, and loses muscle tissue (atrophy). The symptoms of SMA1 first appear at birth or in the first few months of life. Affected babies cannot hold up their head or sit upright. The muscle weakness usually leads to breathing or swallowing issues (bulbar dysfunction). Affected babies have poor muscle tone and have delays in development. This is a serious condition and most affected children do not live past the age of 2 years.
SMA1 is caused by changes (mutations) in the SMN1 gene. This gene provides instructions to make a protein that helps motor neurons work. Motor neurons are cells that send signals from the brain to the muscles. When there are mutations in the SMN1 gene, the motor neurons die off, leading to the symptoms of this condition. SMA1 is inherited in an autosomal recessive way, which means a child must have a mutation in both copies of their SMN1 gene to have the condition.
SMA1 is usually considered in a child who has significant muscle weakness in the first few months of life. Genetic testing of the SMN1 gene is used to confirm the diagnosis. There is no cure for SMA1. Treatments for SMA1 include efforts to maintain the quality of life for an affected baby. These treatments may include support for breathing and feeding. If your child has been diagnosed with SMA1, support groups can help connect you with other affected families.