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Chromosome Analysis, High Resolution

Test code(s) 14595X

Question 1. My patient has a family history of a chromosome abnormality. My patient's chromosomes were reported as normal. Do these results guarantee that my patient does not have the familial chromosome abnormality?

No, please call Quest Genomics Client Services at 866.GENE.INFO to discuss this case with a genetic counselor. Documentation of the specific genetic abnormality in the family will be necessary to determine the appropriateness/pertinence of the testing that was performed on your patient.

Question 2. My patient has a developmental disorder. Chromosomes were reported as normal. Are there other genetic studies that can be done?

Yes, there are other studies that may be appropriate. Please contact Quest Genomics Client Services at 866.GENE.INFO to discuss the case with a genetic counselor and for information on adding additional testing. There are many causes for development disorders, some of which are genetic. In the absence of clinical suspicion for a specific genetic disorder, a microarray analysis is recommended as the first-tier cytogenetic diagnostic test for patients with unexplained developmental delay/intellectual disability, autism spectrum disorders, or multiple congenital anomalies.1 This test can detect subtle deletions and duplications associated with these disorders. If clinical suspicion exists for a specific disorder, there may be other genetic testing available.

Question 3. Which chromosome disorders does high-resolution chromosome analysis rule out?

High resolution chromosome analysis (test code 14595[X]) rules out the following:

  • Trisomies such as trisomy 21 (Down syndrome), trisomy 18, and trisomy 13
  • Sex chromosome abnormalities such as Turner syndrome (45,X) and Klinefelter syndrome (47,XXY)
  • Most balanced or unbalanced rearrangements, including Robertsonian translocations, reciprocal translocations, and inversions
  • Most marker chromosomes
  • Mosaicism above 14% (at a 95% confidence level)

Note that a standard resolution chromosome analysis (test code 14596[X]) is usually sufficient to detect these conditions as well.

Question 4. Which disorders cannot be detected by high-resolution chromosome analysis?

High resolution chromosome analysis (test code 14595[X]) cannot detect the following:

  • Most microdeletion syndromes, including DiGeorge, Prader-Willi, Angelman, Williams, and Smith-Magenis syndromes
  • Mosaicism below 14% (at a 95% confidence level)
  • Fragile X syndrome
  • Single-gene disorders such as cystic fibrosis, Marfan syndrome, neurofibromatosis, etc.
  • Very small or subtle gains, losses, or rearrangements

Question 5. How is this test different from routine chromosome analysis?

High-resolution studies have a resolution of greater than 550 bands, while the standard (routine) resolution studies have a level of approximately 400-550 bands. High resolution allows a more detailed analysis of chromosome structure, which enables detection of more subtle chromosome abnormalities. High-resolution chromosome analysis is suggested for patients who have a family history of a particular abnormality and for patients who have very specific clinical features.

Reference

  1. Miller DT, Adam MP, Aradhya S, et al. Consensus statement: chromosomal microarray is a first-tier clinical diagnostic test for individuals with developmental disabilities or congenital anomalies. Am J Hum Genet. 2010;86:749-764. 
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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