Precursor of cholesterol and vitamin D3. It is reduced to cholesterol by the enzyme 3beta-hydroxysterol-Delta7-reductase (DHCR7) in the last step of cholesterol biosynthesis. Mutations in the gene encoding DHCR7 lead to increased levels of 7-DHC and the neurodevelopmental syndrome Smith-Lemli-Opitz syndrome (SLOS). 7-DHC is used as a biomarker for SLOS screenings. Inhibits human fibroblast sphingomyelinase. Shown to have cytotoxic effects on melanoma cells. In skin, photolysis of 7-DHC by ultraviolet light produces vitamin D3. UV/Vis: lambdamax 271, 282, 293nm.