Defective conversion of 7-dehydrocholesterol to cholesterol in cultured skin fibroblasts from Smith-Lemli-Opitz syndrome homozygotes.
The Smith-Lemli-Opitz syndrome is a common birth defect syndrome characterized biochemically by low plasma cholesterol levels and high concentrations of the cholesterol precursor 7-dehydrocholesterol. The present study was undertaken to prove that the enzyme defect is at the step in which 7-dehydrocholesterol is converted into cholesterol and to establish a new biochemical method for the diagnosis of this disease. We assayed the latter part of the cholesterol biosynthetic pathway by incubating [3H]lathosterol (the immediate precursor of 7-dehydrocholesterol) with cultured skin fibroblasts from 15 homozygous patients, 14 obligate heterozygous parents, and 8 controls, and measuring its conversion to 7-dehydrocholesterol and cholesterol. The formation of cholesterol from lathosterol in parents was not significantly different from that in controls. In contrast, cells from patients made very little cholesterol (P < 0.0001, patients vs. parents or vs. controls) but readily converted lathosterol to 7-dehydrocholesterol. The defect was especially profound in a subgroup of 8 of the most severely clinically affected patients, as virtually no label was detected in the cholesterol fraction. These results provide compelling evidence that 1) this disease is caused by a primary defect in 7-dehydrocholesterol delta 7-reductase, an essential enzyme in the biosynthesis of cholesterol; 2) the most clinically severe form of the syndrome may be associated with the most inhibited enzyme; and 3) the enzyme lathosterol 5-desaturase that converts lathosterol to 7-dehydrocholesterol is fully intact. The present method using fibroblast and amniocyte cultures establishes it as a useful procedure for the biochemical diagnosis of this syndrome.
Honda
A
A
Department of Medicine, Veterans Affairs Medical Center, East Orange, NJ 07018, USA.
Tint
G S
GS
Salen
G
G
Batta
A K
AK
Chen
T S
TS
Shefer
S
S
D000293:Adolescent; D000328:Adult; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D002784:Cholesterol / Q000378:metabolism*; D003684:Dehydrocholesterols / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D008297:Male; D010088:Oxidoreductases / Q000172:deficiency / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D012867:Skin / Q000378:metabolism; D019082:Smith-Lemli-Opitz Syndrome / Q000378:metabolism*; D014316:Tritium
D003684:Dehydrocholesterols; C033144:lathosterol delta-5-dehydrogenase; D014316:Tritium; C001521:lathosterol; D002784:Cholesterol; C016705:7-dehydrocholesterol; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019995:7-dehydrocholesterol reductase