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Journal of Lipid Research, Vol. 42, 366-371, March 2001
Copyright © 2001 by Lipid Research, Inc.

Original Article

Oxysterols in the circulation of patients with the Smith-Lemli-Opitz syndrome: abnormal levels of 24S- and 27-hydroxycholesterol

Correspondence to: Ingemar Björkhem, To whom correspondence should be addressed., Ingemar.Bjorkhem{at}chemlab.hs.sll.se (E-mail)

Infants with the cholesterol synthesis defect Smith- Lemli-Opitz syndrome (SLO) have reduced activity of the enzyme 7-dehydrocholesterol-7-reductase and accumulate 7-dehydrocholesterol, with the highest concentration in the brain. As a result of the generally reduced content of cholesterol, plasma levels of oxysterols would be expected to be reduced. 24S-hydroxycholesterol is almost exclusively formed in the brain, whereas 27-hydroxycholesterol is mainly formed from extrahepatic and extracerebral cholesterol. In accordance with the expectations, sterol-correlated plasma levels of 24S-hydroxycholesterol were reduced in infants with SLO (by about 50%). In contrast, the sterol-correlated levels of 27-hydroxycholesterol in the circulation were markedly increased. No side-chain oxidized metabolites of 7-dehydrocholesterol were detected in the circulation. Recombinant human CYP27 had markedly lower 27-hydroxylase activity toward 7-dehydrocholesterol than towards cholesterol. HEK293 cells expressing 24S-hydroxylase active toward cholesterol had no significant activity towards 7-dehydrocholesterol. The plasma levels of 3ß,7-dihydroxy-5-cholestenoic in the patients acid were reduced, suggesting a generally reduced metabolism of 27-oxygenated steroids.

It is concluded that the accumulation of 7-dehydrocholesterol in the brains of patients with SLO reduces formation of 24S-hydroxycholesterol. The condition is associated with markedly increased circulating levels of 27-hydroxycholesterol, most probably due to reduced metabolism of this oxysterol. We discuss the possibility that the circulating levels of 24S-hydroxycholesterol may be used as a marker for the severity of the disease.—Björkhem, I., L. Starck, U. Andersson, D. Lütjohann, S. von Bahr, I. Pikuleva, A. Babiker, and U. Diczfaulsy. Oxysterols in the circulation of patients with the Smith-Lemli-Opitz syndrome: abnormal levels of 24S- and 27-hydroxycholesterol. J. Lipid Res. 2001. 42: 366;–371.

Supplementary key words: CYP7B, CYP27, CYP46, 7-dehydrocholesterol, brain sterols

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