Use of test
Purpose:
Deletion of the SHOX gene can cause short stature and bone malformations. There are usually two copies of the SHOX gene on the X and Y Chromosomes (one copy on each). The loss of one copy results in a less severe disorder (Leri-Weill dyschondrosteosis) than loss of both copies (Langer mesomelic dysplasia). 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 does not exclude a clinical diagnosis as there are other mutations which can cause the syndrome. Microarray testing can pick up smaller deletions within the SHOX gene.
Ethical Considerations:
These mutations are usually de novo and do not increase the risk of this disorder in siblings or other relatives. However a parent and other relatives may carry a balanced translocation involving this chromosome region and be at increased risk of having an affected child.
Methodology:
Fluorescent in situ hybridisation (FISH) analysis using probes located within the SHOX gene.
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:
15 business days for karyotype and FISH study; 3 business days for FISH alone.
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.