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Prader-Willi syndrome FISH

Also known as: 15q11.2q13 microdeletion

Test category:

Paediatric - Congenital disorder

Use of test

Purpose:

Deletion of genes on the long arm of Chromosome 15 can cause a characteristic syndrome of abnormal neurodevelopment and malformations called Prader-Willi syndrome (PWS). 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 does not exclude the diagnosis of Prader-Willi syndrome as there are other mutations on Chromosome 15 which can cause the syndrome; further studies may be warranted.

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 15q.

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.

>Link to Microarray test

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.

Click here for our billing policy.