8-dehydro Cholesterol (8-DHC) is an isomer of the cholesterol precursor 7-DHC .[1][2][3] It accumulates in tissues and plasma in patients with Smith-Lemli-Opitz syndrome (SLOS), a disorder characterized by a mutation in DHCR7, the gene encoding 3β-hydroxysterol-Δ7-reductase, and decreased cholesterol levels in bodily tissues and fluids, as well as microcephaly, intellectual disability, and distinctive dysmorphic features. 8-DHC levels are increased in serum in a rat model of SLOS induced by the DHCR7 inhibitor AY 9944 .[1][2][3]

Reference:
[1]. Wolf, C., Chevy, F., Pham, J., et al. Changes in serum sterols of rats treated with 7-dehydrocholesterol-Δ7-reductase inhibitors: Comparison to levels in humans with Smith-Lemli-Opitz syndrome. J. Lipid. Res. 37(6), 1325-1333 (1996).
[2]. Bjorkhem, I., Starck, L., Andersson, U., et al. Oxysterols in the circulation of patients with the Smith-Lemli-Opitz syndrome: Abnormal levels of 24S- and 27-hydroxycholesterol. J. Lipid Res. 42(3), 366-371 (2001).
[3]. Griffiths, W.J., Abdel-Khalik, J., Crick, P.J., et al. Sterols and oxysterols in plasma from Smith-Lemli-Opitz syndrome patients. J. Steroid Biochem. Mol. Biol. 169, 77-87 (2017).