Spastic paraplegia type 4 (also known as SPG4) is the most common of a group of genetic disorders known as hereditary spastic paraplegias. These disorders are characterized by progressive muscle stiffness (spasticity) in the legs and difficulty walking. Hereditary spastic paraplegias are divided into two types: pure and complex. The pure types generally involve only spasticity of the lower limbs and walking difficulties. The complex types involve more widespread problems with the nervous system; the structure or functioning of the brain; and the nerves connecting the brain and spinal cord to muscles and sensory cells that detect sensations such as touch, pain, heat, and sound (the peripheral nervous system). In complex forms, there can also be features outside of the nervous system. Spastic paraplegia type 4 is usually a pure hereditary spastic paraplegia, although a few complex cases have been reported.
Mutations in the SPAST gene cause spastic paraplegia type 4. The SPAST gene provides instructions for producing a protein called spastin. Spastin is found throughout the body, particularly in certain nerve cells (neurons). The spastin protein plays a role in the function of microtubules, which are rigid, hollow fibers that make up the cell's structural framework (the cytoskeleton). Microtubules are also involved in transporting cell components and facilitating cell division. Spastin likely helps restrict microtubule length and disassemble microtubule structures when they are no longer needed. Mutations in spastin impair the microtubules' ability to transport cell compartments (organelles), especially in nerve cells; researchers believe this contributes to the major signs and symptoms of spastic paraplegia type 4.
The prevalence of spastic paraplegia type 4 is estimated to be 2 to 6 in 100,000 people worldwide.
This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.
Published Date: July 01, 2020Published By: National Institutes of Health