Smith-Lemli-Opitz Syndrome

Gene : DHCR7

What is Smith-Lemli-Opitz Syndrome?

Smith-Lemli-Opitz Syndrome (SLOS) is an inherited disorder in which a person's body cannot properly make and use cholesterol due to the deficiency of the enzyzme 7-dehydrocholesterol reductase. Cholesterol is important for normal development of many organs in the body, including the brain. Babies who are more severely affected with SLOS are born small, do not grow well, and have a small head size. They may also have physical problems that may include cleft palate, heart defects, extra fingers and toes, and fused second and third toes. Severely affected males may have poorly formed genitals. As these children grow, they may begin to exhibit behavioral problems such as hyperreactivity, irritability or autism spectrum behaviors. People with SLOS may have moderate to severe intellectual disability. Individuals with milder forms may only have a few, less severe symptoms, with mild to no intellectual disability. These mildly affected individuals may have a normal lifespan, whereas severely affected individuals may die as babies. There is no cure for SLOS syndrome, but medical surveillance and care may help to improve some symptoms and overall conditions of life. SLOS is caused by pathogenic variants in the DHCR7 gene.

How is Smith-Lemli-Opitz Syndrome inherited?

SLOS is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for SLOS. However, the risk to have a child affected with SLOS is increased. Testing of reproductive partners is recommended for carriers of SLOS.

How common is Smith-Lemli-Opitz Syndrome?

SLOS is estimated to occur in about 1 in 20,000 to 1 in 40,000 newborns. The actual occurence may be higher because females and mildy affected individuals do not always get diagnosed. SLOS is more common in Caucasian people and less common in people of African or Asian ancestry.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems






GI Tract


Carrier Rates
Detection Rate
Carrier Frequency
Ashkenazi Jewish > 99% 1 in 36
General Population > 99% 1 in 100
Northern European Caucasian > 99% 1 in 50

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