22q11.2 FISH
Also known as: 22q FISH, 22q11.2 deletion syndrome, DiGeorge syndrome, velocardiofacial syndrome (VCFS), conotruncal anomaly face syndrome (CTAF), Opitz G/BBB syndrome, Cayler cardiofacial syndrome, Shprintzen syndrome, CATCH22
Test category:
Paediatric - Congenital disorder
Use of test
Purpose:
Deletions of the proximal long arm of Chromosome 22 (22q) cause a characteristic syndrome of developmental delay and malformations. The syndrome is called DiGeorge syndrome (DGS) or velo-cardio-facial syndrome (VCFS). The deletion may be too small to be seen by conventional chromosome studies. This test provides diagnostic information.
Utility:
In an affected person, an abnormal result is diagnostic of this microdeletion syndrome. Further family studies may clarify the recurrence risk in relatives.
A normal result makes it unlikely that the patient has this disorder.
Ethical considerations:
These mutations are often de novo and do not increase the risk of this disorder in siblings or other relatives. However a parent and other relatives may have the same deletion (and lack obvious features of the disorder) and yet be at risk of having an affected child.
Methodology:
Fluorescent in situ hybridisation (FISH) analysis using probes located within 22q. Deletions that are smaller than the probe may not be detected.
Requesting the test
Ordering:
This test is usually requested by a paediatrician or clinical geneticist. A full karyotype is usually requested at the same time.
Sample required:
2-5 mL blood in EDTA and 2-5 mL blood in lithium heparin. Specimens may be collected by the requesting practitioner or at any Sonic Healthcare collection centre (see link below).
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We recommend that the patient or another adult check the labelling of request forms and sample tubes.
>Link to Sonic Healthcare collection centres
Special instructions:
If the clinical diagnosis is uncertain, it may be preferable to request a microarray study rather than this specific FISH test as a microarray screens for microdeletions and duplications across all chromosomes.
Turnaround time:
5 business days.
Price:
This test has a Medicare rebate which, subject to the requirements of the Medicare descriptor being met, may cover all or part of the cost.
Rebate:
The Medicare details, including descriptor and schedule fee, are listed under MBS item 73291.