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FISH, Smith-Magenis
Test Code14611
CPT Codes
88271, 88273
Physician Attestation of Informed Consent
This germline genetic test requires physician attestation that patient consent has been received if ordering medical facility is located in AK, DE, FL, GA, IA, MA, MN, NV, NJ, NY, OR, SD or VT or test is performed in MA.
Preferred Specimen
5 mL whole blood collected in a sodium heparin (green-top) tube
Minimum Volume
1 mL
Other Acceptable Specimens
Whole blood collected in: Sodium heparin (royal blue-top) or sodium heparin lead-free (tan-top)
Instructions
3-5 mL whole blood collected in a sodium heparin tube. Specimen viability decreases during transit. Send specimen to testing lab for viability determination. Do Not Freeze. Do not reject.
Transport Temperature
Room temperature
Specimen Stability
See Instructions
Methodology
Fluorescence in situ Hybridization (FISH)
FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by the U.S. Food and Drug Administration. The FDA has determined that such clearance or approval is not necessary. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
Set up: Daily; Report available: 5-7 days
Clinical Significance
This test is used in the diagnosis of Smith-Magenis syndrome (SMS), a genetic disorder caused by a deletion at chromosome 17p11.2. SMS is characterized by distinctive facial features, skeletal malformations, developmental delay, cognitive impairment, behavioral abnormalities, sleep disturbances, and childhood obesity [1].
Infants born with SMS often have feeding difficulties, hypotonia, and failure to thrive. As the child ages, characteristic facial features and behavioral abnormalities (including sleep disturbances and self-injurious behaviors) become more apparent. Developmental delay, intellectual disability, speech impairment, hearing loss, and physical abnormalities involving the eye, ear, and/or short stature may also be present [1].
Although the 17p11.2 region contains multiple genes, RAI1 was found to be responsible for most clinical manifestations of SMS. Other than deletions at chromosome 17p11.2, pathogenic variants in RAI1 also lead to SMS [1]. Therefore, a negative FISH result does not rule out SMS. Tests such as chromosomal microarray and gene sequencing are often used to identify gene changes and differentiate SMS from other genetic disorders with similar clinical features.
The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.
Reference
1. Smith ACM, et al. Smith-Magenis Syndrome. In: Adam MP, et al., ed. GeneReviews®. University of Washington; March 3, 2009. Accessed September 29, 2021. https://www.ncbi.nlm.nih.gov/books/NBK1310/
Infants born with SMS often have feeding difficulties, hypotonia, and failure to thrive. As the child ages, characteristic facial features and behavioral abnormalities (including sleep disturbances and self-injurious behaviors) become more apparent. Developmental delay, intellectual disability, speech impairment, hearing loss, and physical abnormalities involving the eye, ear, and/or short stature may also be present [1].
Although the 17p11.2 region contains multiple genes, RAI1 was found to be responsible for most clinical manifestations of SMS. Other than deletions at chromosome 17p11.2, pathogenic variants in RAI1 also lead to SMS [1]. Therefore, a negative FISH result does not rule out SMS. Tests such as chromosomal microarray and gene sequencing are often used to identify gene changes and differentiate SMS from other genetic disorders with similar clinical features.
The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.
Reference
1. Smith ACM, et al. Smith-Magenis Syndrome. In: Adam MP, et al., ed. GeneReviews®. University of Washington; March 3, 2009. Accessed September 29, 2021. https://www.ncbi.nlm.nih.gov/books/NBK1310/
