Neurodevelopmental disorders
Neurodevelopmental disorders
Chromosomal microarray is a genome wide screen for the detection of genetic imbalance with higher resolution and abnormality rate than karyotype analysis
Sample requirements
To request a microarray test please send blood samples, well mixed, in EDTA (3-5ml) to Cytogenetics. Only one sample tube is required. For patients who are difficult to bleed, we will attempt to process smaller samples. Click here for the GLH Rare and Inherited Disease referral form.
Please note that blood samples in lithium heparin tubes are not required for microarray alone tests.
For parental follow up samples, however, we may still request blood specimens in both EDTA (3-5ml) and lithium heparin (1-2ml) in the probands report. This is because sometimes we need to exclude a balanced parental rearrangement by FISH or karyotype. For sample labelling, sample tube guide and referral form criteria see referral requirements.
For accurate interpretation of the array result include full clinical details of the patient and relevant family members including cytogenetic laboratory references.
Acceptance and rejection criteria
For microarray testing blood in any tube other than EDTA will not be processed. The preferred volume is larger than 1ml but for smaller volumes (>0.25ml) processing will be attempted but the test may be unsuccessful.
Referral categories
For optimum interpretation of the microarray result, please provide a full clinical description of the patient.
Microarray testing has replaced karyotype analysis for patients with:
- Developmental delay
- Learning disability
- Facial dysmorphism or congenital abnormalities
- Hypotonic infant
- Congenital heart disease
Please select the most appropriate code for the tests required using the current National genomic test directory for rare and inherited disease and the Rare and inherited disease eligibility criteria. Ctl F will allow search of both of these documents. Please include the appropriate code on the referral form.
The most frequently used codes for microarray only are:
R28 – Congenital malformation and dysmorphism syndromes – microarray only
Testing criteria: clinical features strongly suggestive of a chromosomal cause.
R377 – Intellectual disability – microarray only
Testing criteria: Unexplained moderate/severe/profound global developmental delay or unexplained moderate/severe/profound intellectual disability.
Some clinical indications for which microarrays are indicated have their own codes.
If tests in addition to a microarray are required, please use appropriate code(s) for this from the test directory.
Some copy number changes (CNVs) may be reported as of uncertain significance and cannot be fully interpreted without investigation of parental samples. If required, parental blood samples will be requested in the report and a targeted analysis carried out for the copy number change observed in the original test of the proband. Microarray may detect incidental CNVs which may have implications for other family members.
Microarray will not exclude:
- Balanced rearrangements
- Point mutations
- Fragile X
- Single gene disorders
- Some cases of Prader-Willi or Angelman Syndrome
- Some cases of mosaicism
Please indicate at referral if additional testing for the conditions listed above is required.
Limitations
Please see our limitations of testing page.
Storage and further testing
DNA from EDTA samples is stored for at least 30 years within Molecular Genetics. Subsequent genetic testing can be requested at any time but may not be possible depending on the quality of the material available.
Page last updated 15/10/2024. Please note that if printed, the information is only valid on the day of printing.