Smith-Lemli-Opitz syndrome (SLOS) is a metabolic disorder caused by a mutation in the DHCR7 (7-dehydrocholesterol reductase) gene on chromosome 11. This gene codes for an enzyme that is involved in the production of cholesterol. People who have SLOS are unable to make enough cholesterol to support normal growth and development. Cholesterol is an essential component of the cell membrane and tissues of the brain. A person who cant make enough cholesterol will therefore experience poor growth, developmental delays, and mental retardation. People with this disorder may also have a range of physical malformations (such as extra fingers or toes) and problems with internal organs (such as the heart or kidney).