Spinal muscular atrophy type 1 (SMA1) with congenital bone fractures 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). In addition to muscle weakness and atrophy, SMA1 with congenital bone fractures also causes a baby to be born with broken bones (congenital fractures). Additional features may include short muscles that cause difficulty with movement (joint contractures), low bone density (osteopenia), difficulty breathing, and heart defects. This form of SMA1 is very rare and has only been seen in 5 babies worldwide. It is a serious condition and most affected children have a shortened lifespan.
The exact cause of SMA1 with congenital fractures is unknown. Based on the few known cases, it is believed that this form of SMA is inherited in an autosomal recessive fashion, which means a change (mutation) in two copies of a gene a baby has is needed to have the condition.
SMA1 with congenital bone fractures may be considered in a baby with low muscle tone, muscle weakness, and congenital fractures. Since the gene linked to this condition is not known, genetic testing is not available to confirm the diagnosis. A doctor may collect and examine a small piece of muscle (biopsy) to look for clues of a diagnosis. Treatments for SMA1 with congenital bone fractures include efforts to maintain the quality of life for an affected baby. These treatments may include support for breathing and feeding. If you or a family member has been diagnosed with this disease, talk with your doctor and specialists about the most current treatment options.