Health Topics
Official websites use .gov
A
.gov website belongs to an official government
organization in the United States.
Secure .gov websites use HTTPS
A
lock (
) or https:// means you’ve safely connected to
the .gov website. Share sensitive information only on official,
secure websites.
Normal Function
The CYP7B1 gene is a member of the cytochrome P450 gene family. The enzymes produced from cytochrome P450 genes are involved in the formation and breakdown of various molecules and chemicals within cells. The CYP7B1 gene provides instructions for making an enzyme called oxysterol 7-alpha-hydroxylase. This enzyme is produced primarily in the liver and the brain. In the liver, oxysterol 7-alpha-hydroxylase is involved in the pathway that breaks down cholesterol to form bile acids. Bile acids are a component of a digestive fluid called bile that breaks down fats.
In the brain, oxysterol 7-alpha-hydroxylase is involved in a pathway that converts certain forms of cholesterol into hormones called neurosteroids. Neurosteroids increase the ability of nerve cells (neurons) to send signals (excitability). Oxysterol 7-alpha-hydroxylase helps maintain normal cholesterol levels in the brain and regulates the effects of neurosteroids on the brain.
Health Conditions Related to Genetic Changes
Spastic paraplegia type 5A
Genetic changes that cause disease are called pathogenic variants. Pathogenic variants in the CYP7B1 gene have been found to cause spastic paraplegia type 5A. This condition is characterized by muscle stiffness (spasticity) and severe weakness of the lower limbs (paraplegia), typically beginning in adolescence.
Most CYP7B1 gene variants reduce the activity of oxysterol 7-alpha-hydroxylase. Other variants can prevent the enzyme from working at all.
In the brain, a lack of functioning oxysterol 7-alpha-hydroxylase prevents the production of neurosteroids and causes cholesterols to accumulate. The abnormal buildup of cholesterols also occurs in the fluid that surrounds and protects the brain and spinal cord (the cerebrospinal fluid or CSF). This impairs nerve cell function and leads to cell death. Low levels of neurosteroids likely further impair nerve cell function by affecting their signaling ability. The loss of nerve cells results in the deterioration of nervous system functions (neurodegeneration) and causes the movement problems, weakness, and other signs and symptoms that are characteristic of spastic paraplegia type 5A.
In the liver, reduced oxysterol 7-alpha-hydroxylase activity does not seem to affect the breakdown of cholesterols or the production of bile acid. Another pathway in the liver can perform these functions, which likely explains why people with spastic paraplegia type 5A do not have liver problems that are related to this condition.
More About This Health ConditionOther Names for This Gene
- CBAS3
- CP7B
- cytochrome P450 7B1
- oxysterol 7-alpha-hydroxylase
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- Arnoldi A, Crimella C, Tenderini E, Martinuzzi A, D'Angelo MG, Musumeci O, Toscano A, Scarlato M, Fantin M, Bresolin N, Bassi MT. Clinical phenotype variability in patients with hereditary spastic paraplegia type 5 associated with CYP7B1 mutations. Clin Genet. 2012 Feb;81(2):150-7. doi: 10.1111/j.1399-0004.2011.01624.x. Epub 2011 Jan 31. Citation on PubMed
- Darios F, Mochel F, Stevanin G. Lipids in the Physiopathology of Hereditary Spastic Paraplegias. Front Neurosci. 2020 Feb 28;14:74. doi: 10.3389/fnins.2020.00074. eCollection 2020. Citation on PubMed
- Goizet C, Boukhris A, Durr A, Beetz C, Truchetto J, Tesson C, Tsaousidou M, Forlani S, Guyant-Marechal L, Fontaine B, Guimaraes J, Isidor B, Chazouilleres O, Wendum D, Grid D, Chevy F, Chinnery PF, Coutinho P, Azulay JP, Feki I, Mochel F, Wolf C, Mhiri C, Crosby A, Brice A, Stevanin G. CYP7B1 mutations in pure and complex forms of hereditary spastic paraplegia type 5. Brain. 2009 Jun;132(Pt 6):1589-600. doi: 10.1093/brain/awp073. Epub 2009 May 12. Citation on PubMed
- Hedera P. Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview. 2000 Aug 15 [updated 2025 Jun 5]. In: Adam MP, Bick S, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026. Available from http://www.ncbi.nlm.nih.gov/books/NBK1509/ Citation on PubMed
- Theofilopoulos S, Griffiths WJ, Crick PJ, Yang S, Meljon A, Ogundare M, Kitambi SS, Lockhart A, Tuschl K, Clayton PT, Morris AA, Martinez A, Reddy MA, Martinuzzi A, Bassi MT, Honda A, Mizuochi T, Kimura A, Nittono H, De Michele G, Carbone R, Criscuolo C, Yau JL, Seckl JR, Schule R, Schols L, Sailer AW, Kuhle J, Fraidakis MJ, Gustafsson JA, Steffensen KR, Bjorkhem I, Ernfors P, Sjovall J, Arenas E, Wang Y. Cholestenoic acids regulate motor neuron survival via liver X receptors. J Clin Invest. 2014 Nov;124(11):4829-42. doi: 10.1172/JCI68506. Epub 2014 Oct 1. Citation on PubMed
- Tsaousidou MK, Ouahchi K, Warner TT, Yang Y, Simpson MA, Laing NG, Wilkinson PA, Madrid RE, Patel H, Hentati F, Patton MA, Hentati A, Lamont PJ, Siddique T, Crosby AH. Sequence alterations within CYP7B1 implicate defective cholesterol homeostasis in motor-neuron degeneration. Am J Hum Genet. 2008 Feb;82(2):510-5. doi: 10.1016/j.ajhg.2007.10.001. Epub 2008 Jan 18. Citation on PubMed or Free article on PubMed Central
- Xing C, Huang X, Wang D, Yu D, Hou S, Cui H, Song L. Roles of bile acids signaling in neuromodulation under physiological and pathological conditions. Cell Biosci. 2023 Jun 12;13(1):106. doi: 10.1186/s13578-023-01053-z. Citation on PubMed
The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.