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Test ID: SLO Smith-Lemli-Opitz Screen, Plasma

Reporting Name

Smith-Lemli-Opitz Scrn, P

Useful For

Diagnosis of Smith-Lemli-Opitz syndrome (7-dehydrocholesterol reductase deficiency)

Clinical Information

Cholesterol plays an essential role in many cellular and developmental processes. In addition to its role as a membrane lipid, it is the precursor to numerous molecules that play important roles in cell growth and differentiation, protein glycosylation, and signaling pathways. The biosynthesis of cholesterol and its subsequent conversion to other essential compounds is complex, involving a number of intermediates and enzymes. Disorders that result from a deficiency of these enzymes lead to an accumulation of specific intermediates and inhibit the formation of important biomolecules. Clinical findings common to cholesterol biosynthesis disorders include congenital skeletal malformations, dysmorphic facial features, psychomotor retardation, and failure to thrive.


Smith-Lemli-Opitz syndrome (SLO) is an autosomal recessive disorder caused by variants in the DHCR7 gene leading to a deficiency of the 7-dehydrocholesterol reductase enzyme. It is characterized biochemically by markedly increased plasma concentrations of 7-dehydrocholesterol (7-DHC) and 8-dehydrocholesterol (8-DHC) levels. Clinically, features can include microcephaly, growth retardation, developmental delay, dysmorphic facial features, cleft palate, limb abnormalities (especially 2-3 syndactyly of the toes and postaxial polydactyly), and heart and kidney malformations. However, the clinical spectrum ranges from mild to severe with some mildly affected individuals presenting with only 2 to 3 toe syndactyly and mild cognitive impairment. The reported incidence is between 1 in 10,000 and 1 in 60,000, but it may be more prevalent due to underdiagnoses of mildly affected individuals.


Other disorders of cholesterol biosynthesis, including desmosterolosis (desmosterol reductase deficiency) and sitosterolemia, may present with similar manifestations. These disorders can be detected biochemically by performing a quantitative profile of plasma sterols (STER / Sterols, Plasma).


Elevated plasma concentrations of 7-dehydrocholesterol (7-DHC) and 8-dehydrocholesterol (8-DHC) are highly suggestive of a biochemical diagnosis of Smith-Lemli-Opitz (SLO).


Mild elevations of these cholesterol precursors can be detected in patients with hypercholesterolemia and patients treated with haloperidol. However, the 7-DHC to cholesterol ratio is only elevated in SLO patients.

Analytic Time

3 days

Day(s) and Time(s) Performed

Tuesday, Friday; 8 a.m. (not reported on Saturday or Sunday)

Clinical Reference

1. Haas D, Kelley RI, Hoffmann GF: Defects of cholesterol biosynthesis. In: Sarafoglou K, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. McGraw-Hill Medical; 2009:313-321

2. Nowaczyk MJM: Smith-Lemli-Opitz Syndrome. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; November 13, 1998. Updated January 30, 2020. Accessed July 20, 2020. Available at

3. Hall P, Michels V, Gavrilov D, et al: Aripiprazole and trazodone cause elevations of 7-dehydrocholesterol in the absence of Smith-Lemli-Opitz Syndrome. Mol Genet Metab. 2013 Sep-Oct;110(1-2):176-178

Method Name

Gas Chromatography-Mass Spectrometry (GC-MS)

Specimen Type


Specimen Required

Collection Container/Tube:

Preferred: Green top (sodium or lithium heparin)

Acceptable: Lavender top (EDTA), pearl white top (EDTA/gel tubes), yellow top (ACD A) or yellow top (ACD B)

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Centrifuge and aliquot plasma into plastic vial.

2. Send plasma frozen.

Specimen Minimum Volume

0.2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Frozen (preferred) 90 days
  Refrigerated  90 days

Reference Values

Negative (reported as positive or negative)

Quantitative results are provided when positive.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
SLO Smith-Lemli-Opitz Scrn, P 33275-9


Result ID Test Result Name Result LOINC Value
81595 Smith-Lemli-Opitz Scrn, P 33275-9
29972 Interpretation 59462-2
29974 Reviewed By 18771-6


If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen. 

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Pediatric, mml-Neurometabolic