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CYP7B1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CYP7B1 gene

The CYP7B1 gene produces an enzyme critical for cholesterol breakdown in the liver and the production of neurosteroids in the brain.

Normal Function

The CYP7B1 gene provides instructions for making the enzyme oxysterol 7-alpha-hydroxylase, which is primarily produced in the liver and brain.

  • In the liver: It is involved in the pathway that breaks down cholesterol to form bile acids, which are necessary for fat digestion.
  • In the brain: It converts cholesterol into neurosteroids, which increase the signaling ability (excitability) of neurons and help maintain normal cholesterol levels in the brain.

Health Conditions Related to Genetic Changes

Spastic paraplegia type 5A

Pathogenic variants in the CYP7B1 gene cause spastic paraplegia type 5A, a condition characterized by muscle stiffness (spasticity) and severe weakness of the lower limbs (paraplegia).

The condition occurs because:

  • A lack of functional oxysterol 7-alpha-hydroxylase prevents neurosteroid production.
  • Cholesterol accumulates in the brain and cerebrospinal fluid.
  • The resulting impairment of nerve cell signaling and cell death leads to neurodegeneration.

Interestingly, because the liver has alternative pathways to break down cholesterol and produce bile acids, individuals with this condition typically do not experience liver-related symptoms.

Other Names for This Gene

  • CBAS3
  • CP7B
  • cytochrome P450 7B1
  • oxysterol 7-alpha-hydroxylase

Frequently Asked Questions

The gold standard is targeted sequencing of the CYP7B1 gene, which can identify pathogenic missense, nonsense, or splice‑site variants. If a single heterozygous variant is found, a second‑pass sequencing or multiplex ligation‑dependent probe amplification (MLPA) can detect large deletions or duplications. Whole‑exome sequencing may also reveal CYP7B1 variants when the clinical picture is atypical.
Currently, treatment is symptomatic: baclofen or tizanidine for spasticity, physiotherapy for mobility, and antiepileptics if seizures occur. Some clinicians trial high‑dose vitamin E or omega‑3 fatty acids, but evidence is limited. Research into cholesterol‑lowering agents or neurosteroid precursors is ongoing, but no approved disease‑modifying therapy exists yet.
Because CYP7B1’s primary role in the liver is compensated by alternative pathways, most patients maintain normal bile acid synthesis and liver enzyme levels. Routine liver function tests are usually normal, and there is no need for specialized hepatic monitoring beyond standard care unless symptoms suggest otherwise.
SPG5A typically presents in the second or third decade with progressive lower‑limb spasticity, weakness, and gait difficulty. Key distinguishing features include the presence of mild cognitive impairment, early onset of urinary urgency, and occasional mild optic atrophy. Unlike some other SPG types, liver function tests remain normal, and there is no significant peripheral neuropathy. Early MRI may show thinning of the corpus callosum and corticospinal tract hyperintensities.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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