ABNORMAL CHOLESTEROL-BIOSYNTHESIS AS IN SMITH-LEMLI-OPITZ-SYNDROME DISRUPTS NORMAL SKELETAL DEVELOPMENT IN THE RAT

Smith-Lemli-Opitz syndrome (SLOS) in human infants in a common autosom al recessive malformation syndrome (estimated incidence, 1:20,000). It is characterized clinically by congenital anomalies, especially crani ofacial and limb defects, and biochemically by a defect in 7-dehydroch olesterol-Delta 7-reductase activity (7DHC-reductase), the final enzym e in cholesterol biosynthesis. In previous studies, early administrati on of the 7DHC-reductase inhibitor AY9944 to pregnant rats resulted in a high frequency of holoprosencephaly, relevant to craniofacial anoma lies of SLOS. In order to test the effect of AY9944 on limb developmen t, we treated dams on gestation day 7 (GD7), which delays the biochemi cal defect to about GD13 to GD14. Sera were sampled on GD12, GD14, and GD21 and cholesterol and dehydrocholesterols (7DHC and 8DHC) were mea sured by gas-chromatography-mass spectrometry (GC-MS), as for the diag nosis of SLOS. GD21 fetuses were examined for gross malformations and skeletal development. In treated dams, the SLOS biochemical marker 7DH C accounted for one fourth and one third of total sterols, respectivel y, on GD12 and GD14, and cholesterolemia on these two gestation days w as reduced by 50% and 43%, respectively, as compared with control valu es. This maternal metabolic defect was associated with decrease in fet al weight and delayed ossification. In addition, scapular malformation s were observed in four fetuses from three litters. The malformations could have been caused by the same mechanism as holoprosencephaly afte r early treatment with AY9944. These cholesterol-deficiency-based malf ormations could have a common cause in the abnormal expression of Hedg ehog or other developmental gene proteins, and may thus explain variou s congenital polymalformative syndromes in humans, including SLOS.