Spastic paraplegia type 5A is one of a group of genetic disorders known as hereditary spastic paraplegias. These disorders are characterized by muscle stiffness (spasticity) and severe weakness in the lower limbs (paraplegia). Hereditary spastic paraplegias are often divided into two types: pure and complex. The pure types involve spasticity and weakness only in the lower limbs, while the complex types involve additional problems with other areas of the body; additional features can include changes in vision, changes in intellectual functioning, brain abnormalities, and disturbances in nerve function (neuropathy). Spastic paraplegia type 5A is usually a pure hereditary spastic paraplegia, although complex type features have been reported in some individuals, usually in those who have had the condition for many years.
Spastic paraplegia type 5A is caused by mutations in the CYP7B1 gene. This gene provides instructions for making an enzyme called oxysterol 7-alpha-hydroxylase. In the brain, oxysterol 7-alpha-hydroxylase is involved in a pathway that converts cholesterol to hormones called neurosteroids. These neurosteroids increase nerve cell activity (excitability) and promote cell survival and communication between nerve cells. Oxysterol 7-alpha-hydroxylase helps maintain normal cholesterol levels in the brain and, by producing neurosteroids through altering existing hormones within the pathway, regulates the effects of neurosteroids on the brain.
Spastic paraplegia type 5A is a rare condition. Its prevalence is unknown.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Published Date: September 01, 2017Published By: National Institutes of Health