GlcA-tetrol, biomarker for the deficiency of sterol 27-hydroxylase, caused by mutations in the CYP27A1 gene. 
 
The absolute amount of GlcA-tetrol in the vial was determined using quantitative NMR to have the stated value on the vial. The vial may have additional components, but none are isobaric with GlcA-tetrol, and these additional components have no effect on the ability to quantify the GlcA-tetrol. 
 
Cerebrotendinous xanthomatosis,  CTX