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.