Correspondence

Diagnosis of Smith-Lemli-Opitz Syndrome

N Engl J Med 1994; 330:1685-1687June 9, 1994

Article

To the Editor:

Tint et al. (Jan. 13 issue)1 reported a biochemical defect in cholesterol biosynthesis that gives rise to a well-recognized dysmorphic syndrome, the Smith-Lemli-Opitz syndrome. Plasma from affected children contains a high concentration of the cholesterol precursor 7-dehydrocholesterol and a low level of cholesterol. The risk of recurrence of this autosomal recessive condition in a subsequent child is 1 in 4, and to date, prenatal ultrasound scanning has been of limited use2.

We have used biochemical testing to perform a successful prenatal diagnosis. The first child of the couple requesting the prenatal diagnosis had the Smith-Lemli-Opitz syndrome, type II. The child had multiple external and internal anomalies and died in the neonatal period. Despite the apparently normal results of detailed ultrasound scanning in the second pregnancy, that child was also affected and died a few days after birth. Apart from the distinctive facial appearance and body shape, a postmortem examination showed only a cleft of the soft palate and unilobular lungs.

During the index pregnancy an amniocentesis was performed at 15 weeks of gestation. Analysis by gas chromatography-mass spectrometry demonstrated an amniotic-fluid cholesterol concentration of 10.7 μmol per liter (control range, 16 to 45 μmol per liter) and a 7-dehydrocholesterol concentration of 6.07 μmol per liter (control range, 0.0012 to 0.0096 μmol per liter). The ratio of 7-dehydrocholesterol to cholesterol in plasma from children with the Smith-Lemli-Opitz syndrome, type II (0.48, 0.64, and 2.24) was similar to the ratio in the amniotic fluid of the fetus (0.57) but much higher than that in plasma from both parents (0.00099 and 0.00087). However, the ratio of 7-dehydrocholesterol to cholesterol in plasma from both parents was twice that in plasma from adult controls (P<0.0005). A chromosome analysis of the amniotic fluid showed a male karyotype. Both detailed prenatal scanning and examination of the fetus after termination of the pregnancy demonstrated female external genitalia, a feature of affected male fetuses. The findings on scanning and postmortem examination confirmed the biochemical diagnosis in the fetus.

The discovery of the underlying biochemical defect in a clinically well-characterized syndrome has allowed an accurate prenatal diagnosis to be made. The elevated ratio of 7-dehydrocholesterol to cholesterol in the parents also suggests the possibility of testing to identify heterozygotes for a condition in which the frequency of carrier status may be as high as 1 to 2 percent3.

Julie McGaughran, B.Sc., M.R.C.P.
Dian Donnai, F.R.C.P.
St. Mary's Hospital, Manchester M13 OJH, United Kingdom

Peter Clayton, M.D., F.R.C.P.
Kevin Mills, B.Sc.
Institute of Child Health, London WC1N 1EH, United Kingdom

3 References

1. 1

   Tint GS, Irons M, Elias ER, et al. Defective cholesterol biosynthesis associated with Smith-Lemli-Opitz syndrome. N Engl J Med 1994;330:107-113
   Full Text | Web of Science | Medline

2. 2

   Johnson JA, Aughton DJ, Comstock CH, von Oeyen PT, Higgins JV, Schulz R. Prenatal diagnosis of Smith-Lemli-Opitz syndrome, type II. Am J Med Genet 1994;49:240-243
   CrossRef | Web of Science | Medline

3. 3

   Chasalow FI, Blethen SL, Taysi K. Possible abnormalities of steroid secretion in children with Smith-Lemli-Opitz syndrome and their parents. Steroids 1985;46:827-843
   CrossRef | Web of Science | Medline

To the Editor:

In their excellent article, Tint et al. reported on defective cholesterol biosynthesis associated with the Smith-Lemli-Opitz syndrome, one of the most common autosomal genetic disorders in the North American white population. Diagnosis rests on the clinical phenotype and the detection of elevated levels of the biosynthetic cholesterol precursor 7-dehydrocholesterol in blood or tissue samples. Unfortunately, the method they used to quantify 7-dehydrocholesterol (capillary-column gas chromatography-mass spectrometry) can be reliably performed only in a highly specialized laboratory not available in most hospitals.

To permit more widespread diagnosis, we have developed a simple spectrophotometric method to quantify free 7-dehydrocholesterol in blood samples. The method was used to diagnose the Smith-Lemli-Opitz syndrome in a dystrophic male child (weight at birth, 2500 g) who had polydactyly, abnormal genitalia, and a plasma cholesterol level of only 34 mg per deciliter at the age of three weeks. Briefly, blood samples (2 ml) obtained in EDTA-treated tubes were extracted with n-hexane (yield of 7-dehydrocholesterol, 97.5 percent), and an ultraviolet spectrum (320 to 250 nm) was subsequently recorded from the concentrated extract (1 ml). The standard spectrum of 7-dehydrocholesterol, with peaks at 294, 285, 272, and 260 nm,1,2 was readily detected in the sample from the patient but not in samples from 10 normal controls (Figure 1Figure 1Ultraviolet-Absorption Spectrum of 7-Dehydrocholesterol in Extracts of Blood Samples from a Patient with the Smith-Lemli-Opitz Syndrome and a Normal Control.). Quantitative evaluation on the basis of an experimentally determined absorptivity of 7200 M^-1 • cm^-1 at 294 nm provided a concentration of 2.9 μmol, representing 112 μg of 7-dehydrocholesterol per deciliter of total blood. This value is 15 times higher than the median in normal adults3 but at least two orders of magnitude below the plasma 7-dehydrocholesterol levels reported by Tint et al. in generally older patients with very similar clinical symptoms (ranging from 12 to 32 mg per deciliter for patients who were 6 months to 13 years of age, according to Table 1 of their paper).

Since we do not expect that the different analytic methods would have a substantial influence on the quantitative results, we conclude that even a relatively moderate elevation of 7-dehydrocholesterol may be associated with a severe phenotype. In addition, the high sensitivity of the assay may, in certain instances, provide a useful tool for identification of heterozygotes, which has not been feasible to date.

Udo Seedorf, Ph.D.
Michael Walter, M.D.
Gerd Assmann, M.D.
Westfalian Wilhelms University, 48129 Munster, Germany

3 References

1. 1

   Kandutsch AA. Enzymatic reduction of the Delta⁷ bond of 7-dehydrocholesterol. J Biol Chem 1962;237:358-362
   Web of Science | Medline

2. 2

   Noland BJ, Arebalo RE, Hansbury E, Scallen TJ. Purification and properties of sterol carrier protein. J Biol Chem 1980;255:4282-4289
   Web of Science | Medline

3. 3

   Axelson M. Occurrence of isomeric dehydrocholesterols in human plasma. J Lipid Res 1991;32:1441-1448
   Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: In reply to McGaughran et al., we are pleased that our recommendation to analyze amniotic fluid for 7-dehydrocholesterol in high-risk pregnancies has been tested by another group of investigators. In the case of a woman who had previously given birth to an affected child, we recently reported cholesterol, 7-dehydrocholesterol, and isomeric dehydrocholesterol II concentrations of 32.6, 14.8, and 6.8 μmol per liter, respectively, in amniotic fluid at 16 weeks and 0.75, 0.49, and 0.47 mmol per liter, respectively, in cord blood at delivery1. At birth, the child had typical features of the less severe type (I) of the Smith-Lemli-Opitz syndrome. During the pregnancy, the mother's plasma cholesterol level always remained below the lower 95 percent confidence limit reported for healthy controls, which suggests that a low maternal plasma cholesterol level may be a risk factor for the syndrome in the fetus. More measurements are needed to establish this method and determine its detection limits, but it does have promise as a prenatal assay for the identification of a homozygous fetus. We also believe that it is essential to measure amniotic-fluid sterols in cases in which the parents are heterozygotes but the fetus is either heterozygous or does not have the defect.

The results reported by Seedorf et al. are very encouraging and suggest that optical absorption may be a useful screening technique. We believe, however, that it should be coupled with a measurement of the plasma cholesterol level if the Smith-Lemli-Opitz syndrome is suspected. If the 7-dehydrocholesterol concentration does prove to be abnormally high, the screening test should be followed by a more comprehensive sterol analysis, because isomeric dehydrocholesterol II,2 which is also a useful diagnostic sterol and which we have tentatively identified as cholest-5,8-dien-3β-ol,3 does not have an absorption peak between 260 and 300 nm. The authors suggest that their method is useful as an assay for free 7-dehydrocholesterol, but we reported that 63 to 83 percent of dehydrocholesterols in plasma from homozygotes for the Smith-Lemli-Opitz syndrome are transported as esters2.

Although there is no reason to believe a priori that the ultraviolet-absorption spectra of free and esterified 7-dehydrocholesterol are not similar, a difference in absorption could account for the low concentration in the patient described by Seedorf et al. We suggest that, to validate the method, parallel measurements of 7-dehydrocholesterol concentrations by capillary gas chromatography and optical absorption be performed before and after the alkaline saponification of sterol esters.

G. Stephen Tint, Ph.D.
Department of Veterans Affairs Medical Center, East Orange, NJ 07018-1095

Gerald Salen, M.D.
University of Medicine and Dentistry-New Jersey Medical School, Newark, NJ 07103

Mira Irons, M.D.
New England Medical Center, Boston, MA 02111

3 References

1. 1

   Abuelo DN, Canick JA, Kelley RI, et al. Prenatal diagnosis of the Smith-Lemli-Opitz syndrome by detection of the cholesterol biosynthetic defect in amniotic fluid. Am J Med Genet 1994;50:333-333 abstract.
   

2. 2

   Tint GS, Irons M, Elias ER, et al. Defective cholesterol biosynthesis associated with the Smith-Lemli-Opitz syndrome. N Engl J Med 1994;330:107-113
   Full Text | Web of Science | Medline

3. 3

   Axelson M. Occurrence of isomeric dehydrocholesterols in human plasma. J Lipid Res 1991;32:1441-1448
   Web of Science | Medline

Citing Articles (10)

Citing Articles

1. 1

   Ingrid Witters, Philippe Moerman, Mieke Cannie, Luc De Catte, Jean-Pierre Fryns. (2008) Prenatal Diagnosis of Smith–Lemli–Opitz Syndrome. Ultrasound 16:4, 208-210
   CrossRef

2. 2

   Mee Rim Park, Jung Min Ko, Chong-Keun Cheon, Gu-Hwan Kim, Han-Wook Yoo. (2008) A case of Smith-Lemli-Opitz syndrome diagnosed by identification of mutations in the 7-dehydrocholesterol reductase (DHCR7) gene. Korean Journal of Pediatrics 51:11, 1236
   CrossRef

3. 3

   John S. Neuberger, Thomas F. Gesell. (2002) RESIDENTIAL RADON EXPOSURE AND LUNG CANCER: RISK IN NONSMOKERS. Health Physics 83:1, 1-18
   CrossRef

4. 4

   Lorraine Cassidy, David Taylor. (1999) Congenital cataract and multisystem disorders. Eye 13:3b, 464-473
   CrossRef

5. 5

   G. S. Tint, Dianne Abuelo, Marianne Till, M. P. Cordier, Ashok K. Batta, Sarah Shefer, Akira Honda, Megumi Honda, Guorong Xu, Mira Irons, Ellen R. Elias, Gerald Salen. (1998) Fetal Smith-Lemli-Opitz syndrome can be detected accurately and reliably by measuring amniotic fluid dehydrocholesterols. Prenatal Diagnosis 18:7, 651-658
   CrossRef

6. 6

   P. SHARP, E. HAAN, J. M. FLETCHER, T. Y. KHONG, W. F. CAREY. (1997) FIRST-TRIMESTER DIAGNOSIS OF SMITH–LEMLI–OPITZ SYNDROME. Prenatal Diagnosis 17:4, 355-361
   CrossRef

7. 7

   MICHAEL NORGARD, JEROME YANKOWITZ, WILLIAM RHEAD, ADAM B. KANIS, BRYAN D. HALL. (1996) PRENATAL ULTRASOUND FINDINGS IN HYDROLETHALUS: CONTINUING DIFFICULTIES IN DIAGNOSIS. Prenatal Diagnosis 16:2, 173-179
   CrossRef

8. 8

   Jon A. Hyett, Peter T. Clayton, Gonzalo Moscoso, Kypros H. Nicolaides. (1995) Increased first trimester nuchal translucency as a prenatal manifestation of Smith-Lemli-Opitz syndrome. American Journal of Medical Genetics 58:4, 374-376
   CrossRef

9. 9

   Dianne N. Abuelo, G. S. Tint, Richard Kelley, Ashok K. Batta, Sarah Shefer, Gerald Salen. (1995) Prenatal detection of the cholesterol biosynthetic defect in the Smith-Lemli-Opitz syndrome by the analysis of amniotic fluid sterols. American Journal of Medical Genetics 56:3, 281-285
   CrossRef

10. 10

    Reimer, G. Michael, . (1994) Radon and Lung Cancer. New England Journal of Medicine 331:16, 1098-1098
    Full Text

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