Rigid spine muscular dystrophy (RSMD), sometimes referred to as rigid spine syndrome (RSS), is a type of congenital muscular dystrophy — a group of diseases characterized by muscle wasting and weakness very early in life. RSMD involves weakness of the muscles of the torso and neck, and can cause spine stiffness and serious breathing problems.
What causes RSMD?
RSMD is caused by mutations in a gene called SELENONÂ (formerly called SEPN1). This gene provides the information necessary to make a protein called selenoprotein N. The function of this protein is not known, but researchers think it may play a role in the formation of muscle tissue during embryonic development. It also may be important for normal muscle function after birth.Â
What are the symptoms of RSMD?
Infants with RSMD generally display muscle weakness either at birth or within the first few months of life. They usually have poor head control and weak muscle tone, which may delay walking or crawling. Over time, the muscles around the spine weaken and the joints of the spine — where vertebrae meet — develop deformities called contractures, which restrict movement. The necks and backs of children with RSMD become stiff and rigid. Children may not be able to move their heads up and down or side to side. Some patients also will develop scoliosis, an abnormal curvature of the spine.
Because of the back problems and muscle weakness caused by RSMD, children with the disease have difficulty breathing, especially at night. These breathing problems can be life-threatening.
How is RSMD diagnosed?
To diagnose RSMD, a physician will take a family history, and perform a physical exam of symptoms. A muscle biopsy — in which a needle is used to collect a small sample of muscle tissue, which is then tested — may be used to observe abnormalities in the muscle.
The best way to diagnose RSMD is a genetic test looking for mutations in SELENON.
How is RSMD treated?
There currently is no cure for RSMD. But there are treatments available to reduce symptoms and improve patient well-being.
Most individuals with RSMD need physiotherapy to build strength, slow muscle loss, and improve range of motion.
There are support braces to help children with scoliosis, and some cases of scoliosis can be treated surgically.
Children with RSMD may have difficulty breathing at night, which may require breathing support — such as additional oxygen, or a machine that supports breathing called a ventilator. The difficulties in breathing may make children more susceptible to respiratory infections.
Last updated: August 26, 2019
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