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DHCR7 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

DHCR7 gene

The DHCR7 gene provides instructions for making the enzyme 7-dehydrocholesterol reductase, which is responsible for the final step of cholesterol synthesis.

Normal Function

The DHCR7 gene provides instructions for making an enzyme called 7-dehydrocholesterol reductase. This enzyme is responsible for the final step in cholesterol production in many types of cells. Specifically, 7-dehydrocholesterol reductase converts a molecule called 7-dehydrocholesterol to cholesterol.

Cholesterol is a waxy, fat-like substance that is produced in the body and obtained from foods that come from animals (particularly egg yolks, meat, poultry, fish, and dairy products). It has important functions both before and after birth. Cholesterol plays a critical role in embryonic development by interacting with signaling proteins that control early development of the brain, limbs, genital tract, and other structures. It is also a structural component of cell membranes and myelin, the fatty covering that insulates nerve cells. Additionally, cholesterol is used to make certain hormones and is important for the production of acids used in digestion (bile acids).

Health Conditions Related to Genetic Changes

Smith-Lemli-Opitz syndrome

More than 200 mutations that cause Smith-Lemli-Opitz syndrome have been identified in the DHCR7 gene. Smith-Lemli-Opitz syndrome is a developmental disorder characterized by distinctive facial features, small head size (microcephaly), intellectual disability or learning problems, and behavioral problems. The most common mutation, which is written as IVS8-1G>C, alters a single DNA building block (nucleotide) in the DHCR7 gene. This change interferes with the normal processing of 7-dehydrocholesterol reductase, resulting in an abnormally short, nonfunctional enzyme.

Most of the known DHCR7 mutations change single amino acids in 7-dehydrocholesterol reductase. These mutations reduce the ability of this enzyme to convert 7-dehydrocholesterol to cholesterol. Other mutations insert or delete nucleotides in the DHCR7 gene or lead to the production of an abnormally short enzyme; these mutations eliminate the activity of the enzyme. Without functional 7-dehydrocholesterol reductase, cells are unable to produce enough cholesterol. In addition, toxic byproducts of cholesterol production (such as 7-dehydrocholesterol) can build up in the blood and other tissues. The combination of low cholesterol levels and an accumulation of harmful substances likely disrupts the growth and development of many body systems. It is not completely understood, however, how either abnormality leads to the specific features of Smith-Lemli-Opitz syndrome.

Other Names for This Gene

  • 7-DHC reductase
  • D7SR
  • delta-7-dehydrocholesterol reductase
  • DHCR7_HUMAN
  • sterol delta-7-reductase

Frequently Asked Questions

Oral supplementation with purified cholesterol or egg-yolk-rich diets helps raise circulating cholesterol levels and normalize bile acid synthesis. In many patients, this leads to improved weight gain, better linear growth, reduced skin sensitivity to sunlight, fewer infections, and reductions in aggressive or self-injurious behaviors. However, because dietary cholesterol does not cross the blood-brain barrier, it does not correct preexisting brain malformations, resolve severe intellectual disability, or cure structural physical anomalies.
The block in the final step of cholesterol conversion causes abnormally high levels of 7-dehydrocholesterol to accumulate in skin cells. When exposed to ultraviolet radiation, 7-DHC and its byproducts undergo phototoxic reactions that trigger rapid sunburns, erythema, and deep tissue damage even after minimal daylight exposure. Management requires strict sun avoidance, UV-protective clothing, and daily broad-spectrum, high-SPF sunscreens.
blood sterol analysis measuring 7-dehydrocholesterol (7-DHC) and 8-dehydrocholesterol levels via gas chromatography-mass spectrometry is the primary biochemical diagnostic test. An elevated 7-DHC concentration, combined with a high 7-DHC to total cholesterol ratio, is diagnostic for Smith-Lemli-Opitz syndrome. Molecular genetic testing of the DHCR7 gene is subsequently used to identify the specific causative variants and confirm the diagnosis.
Yes. Second-trimester maternal serum screening may reveal markedly reduced unconjugated estriol (uE3) levels, often accompanied by low maternal alpha-fetoprotein and hCG. Prenatal ultrasound may show characteristic anomalies such as microcephaly, cleft palate, heart defects, or polydactyly. Definitive prenatal diagnosis is accomplished via chorionic villus sampling (CVS) or amniocentesis by analyzing sterol levels in amniotic fluid or testing fetal DNA directly for familial DHCR7 mutations.
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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