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FISH, Smith-Magenis
Test Code14611
CPT Codes
88271, 88273
Includes
If this test is ordered without routine G-band chromosome analysis, a Tissue Culture charge will be added, (CPT code: 88230). If results are not possible, the test order may be canceled and replaced with a Cytogenetics Communication.
Preferred Specimen
5 mL whole blood collected in 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) tube
Instructions
Clinical history and reason for referral are required with test order.
3-5 mL whole blood collected in a sodium heparin tube.
Specimen viability decreases during transit. Send specimen to testing laboratory for viability determination. Do not freeze. Do not reject.
3-5 mL whole blood collected in a sodium heparin tube.
Specimen viability decreases during transit. Send specimen to testing laboratory for viability determination. Do not freeze. Do not reject.
Transport Temperature
Room temperature
Specimen Stability
Room temperature: See instructions
Refrigerated: See instructions
Frozen: See instructions
Refrigerated: See instructions
Frozen: 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. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
Set up: Mon-Sat; Report available: 14 days
Reference Range
See Laboratory Report
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/
