Smith-Lemli-Opitz Syndrome via the DHCR7 Gene

Summary and Pricing

Test Method

Exome Sequencing with CNV Detection
Test Code Test Copy GenesPrice Test CPT CodeGene CPT Codes Copy CPT Codes
9573 DHCR7$890 8140581405,81479 Add to Order

Pricing Comments

Our favored testing approach is exome based NextGen sequencing with CNV analysis. This will allow cost effective reflexing to PGxome or other exome based tests. However, if full gene Sanger sequencing is desired for STAT turnaround time, insurance, or other reasons, please see link below for Test Code, pricing, and turnaround time information. If the Sanger option is selected, CNV detection may be ordered through Test #600.

The Sanger Sequencing method for this test is NY State approved.

For Sanger Sequencing click here.

Targeted Testing

For ordering sequencing of targeted known variants, go to our Targeted Variants page.

Turnaround Time

18 days on average


Genetic Counselors


Clinical Features and Genetics

Clinical Features

Smith-Lemli-Opitz Syndrome (SLOS) (OMIM 270400) is a deficiency in the enzyme 7-dehydrocholesterol reductase which catalyzes the last step in the biosynthesis of cholesterol. Affected children have high plasma 7-dehydrocholesterol/cholesterol ratios. The enzyme deficiency leads to a variety of developmental problems including growth and mental retardation, 2-3 toe syndactyly, microcephaly, anteverted nares, ptosis, genital abnormalities, heart defects, polydactyly, and photosensitivity. The most severe cases are usually diagnosed in infancy, with milder cases diagnosed in childhood or even adult life. The great majority of SLOS patients have some clinical features of autism (Sikora et al. Am J Med Genet A 140A:1511-1518, 2006).


Smith-Lemli-Opitz Syndrome (SLOS) exhibits autosomal recessive inheritance. Mutations in the DHCR7 gene encoding 7-dehydrocholesterol reductase are the only known cause of SLOS. About 130 causative DHCR7 mutations have been reported to date (Witsch- Baumgartner et al. Hum Mut 17:172-182, 2001; Correa-Cerro and Porter. Mol Genet Metab 84:112-126, 2005). About 90% of these mutations are missense, although “gene knockout” mutations (splicing, nonsense, and frameshift) are also known. Among those with European ancestry, the most common mutations appear to be IVS8-1 G>C, Thr93Met, Trp151Stop, Arg404Cys, and Val326Leu. Carrier rates for SLOS in some populations may be as high as 1/30. Missed diagnoses and especially spontaneous miscarriages may explain the difference between the expected incidence based on carrier rates and the actual incidence of roughly 1/30,000 (Nowaczyk et al. Am J Med Genet A 140A:2057-62, 2006).

Testing Strategy

This test provides full coverage of all coding exons of the DHCR7 gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing.

Since this test is performed using exome capture probes, a reflex to any of our exome based tests is available (PGxome, PGxome Custom Panels).

Clinical Sensitivity - Sequencing with CNV

Using DNA sequencing and characterizing patients by plasma sterol concentrations and clinical features, (Witsch-Baumgartner et al. Am J Hum Genet 66:402-412, 2000) detected two likely causative mutations in 78 out of 84 (93%) SLOS patients and one likely causative mutation in the remaining 6 (7%).

Indications for Test

All patients with biochemical and clinical features of SLOS are candidates for this test. We will also sequence the DHCR7 gene in relatives of patients to determine carrier status. This test may also be considered for the reproductive partners of individuals who carry pathogenic variants in DHCR7.


Official Gene Symbol OMIM ID
DHCR7 602858
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT


Name Inheritance OMIM ID
Smith-Lemli-Opitz Syndrome AR 270400

Related Tests

Autism Spectrum Disorders Panel
Fetal Concerns Panel
Pelger-Huet Anomaly and Greenberg Skeletal Dysplasia via the LBR Gene


  • Correa-Cerro, L. S., Porter, F. D. (2005). "3beta-hydroxysterol Delta7-reductase and the Smith-Lemli-Opitz syndrome." Mol Genet Metab 84(2): 112-26. PubMed ID: 15670717
  • Nowaczyk, M. J., (2006). "DHCR7 mutation carrier rates and prevalence of the RSH/Smith-Lemli-Opitz syndrome: where are the patients?." Am J Med Genet A 140(19): 2057-62. PubMed ID: 16906538
  • Sikora, D. M., (2006). "The near universal presence of autism spectrum disorders in children with Smith-Lemli-Opitz syndrome." Am J Med Genet A 140(14): 1511-8. PubMed ID: 16761297
  • Witsch-Baumgartner, M., (2000). "Mutational spectrum in the Delta7-sterol reductase gene and genotype-phenotype correlation in 84 patients with Smith-Lemli-Opitz syndrome." Am J Hum Genet 66(2): 402-12. PubMed ID: 10677299
  • Witsch-Baumgartner, M., (2001). "Frequency gradients of DHCR7 mutations in patients with Smith-Lemli-Opitz syndrome in Europe: evidence for different origins of common mutations." Eur J Hum Genet 9(1): 45-50. PubMed ID: 11175299


Ordering Options

myPrevent - Online Ordering

  • The test can be added to your online orders in the Summary and Pricing section.
  • Once the test has been added log in to myPrevent to fill out an online requisition form.

Requisition Form

  • A completed requisition form must accompany all specimens.
  • Billing information along with specimen and shipping instructions are within the requisition form.
  • All testing must be ordered by a qualified healthcare provider.

Specimen Types

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