SLOS is caused by an inborn error of cholesterol biosynthesis due to a deficiency of the last enzyme of the cholesterol synthetic pathway, 7-dehydrocholesterol reductase. This leads to a deficency of cholesterol and elevation of the cholesterol precursor, 7-dehydrocholesterol (7-DHC). Diagnosis of affected patients relies upon the demonstration of this characteristic sterol profile.

To determine if standard lipid analysis would identify patients with SLOS, serum was drawn on five patients with SLOS and sent for testing. Standard analysis of lipids revealed a mean cholesterol of 104 mg/dl (range 79-160;normal 131-239), mean triglycerides of 95 mg/dl (range 71-145;normal 50-250), mean VLDL-chol of 19 mg/dl (range 14-29;normal 0-50), mean LDL-chol of 60 mg/dl (range 22-117;normal 80-159), and mean HDL-chol of 26 mg/dl (range 23-32;normal 35-85). Aside from minimally low levels of total cholesterol and LDL and HDL cholesterols, these results are unremarkable.

Specialized sterol analysis by GC-MS revealed that the true mean cholesterol was 78mg/dl (range 45-120); while the remainder of the measured sterols consisted of 7-DHC (mean 12 mg/dl; range 9-16) and 8-DHC (mean 11mg/dl; range 8.8-13).

These data indicate that patients with SLOS would not be identified by standard lipid analysis. Definitive diagnosis of this syndrome therefore rests upon specialized analysis of plasma sterols.