Diagnostic tests

Cytogenetic studies on blood specimens are useful in diagnosing structural and numerical chromosome abnormalities. Patients suitable for these studies include people with

• congenital abnormalities
• developmental delay
• unexplained intellectual disability
• family history of a chromosome abnormality
• primary or secondary amenorrhea
• multiple pregnancy loss or infertility.

Routine cytogenetics

Blood cells need to be induced to divide and produce metaphases for cytogenetic analysis. The time taken for a standard sample to be cultured, have specialised staining and microscopic analysis is approximately 10 days.

We endeavour to obtain a result within 14 days. The majority of bloods are reported within the range 10-14 days. Inadequate samples may prolong the analysis time.

Techniques are available to obtain preliminary results in specific urgent cases (usually 2-3 days).

Additional requests for further testing eg FISH, subtelomere and breakage studies may lengthen the turnaround time.

FISH testing

For certain microdeletion and microduplication syndromes, FISH testing is available. The more common of these include:

• 1p36 microdeletion syndrome
• Wolf-Hirschhorn syndrome(4p16.3)
• Cri-du-chat syndrome (5p15)
• Sotos syndrome (5q35)
• Williams syndrome (7q11.23)
• Kabuki syndrome (test in development)
• Langer Giedion syndrome (8q24.1)
• Beckwith-Wiedemann syndrome (11p15)
• Wilms/aniridia/genital urinary/mental retardation syndrome (WAGR) (11p13)
• Retinoblastoma (13q14)
• Angelman syndrome (15q11-12)
• Prader-Willi syndrome (15q11-12)
• Miller-Dieker syndrome (17p13.3)
• Smith-Magenis syndrome (17p11.2)
• Familial Neuropathies (CMT 1A, HNPP)(17p11.2)
• 22q11.2 microdeletion syndromes (DiGeorge/Velocardiofacial/CATCH 22)
• Leri-Weill syndrome (Xp22.33, Yp11.3)

Specimen requirements

For adults and children a minimum of 5 mL of whole blood (babies - minimum 1 mL) in a lithium heparin tube is the optimum sample. Mix thoroughly. Do not spin. Blood should be kept cool but not frozen in transit.

The request form should be completed with name and date of birth of patient, comprehensive clinical details, specific test requirements and a legible name and contact details for the referring practitioner.

Breakage syndromes

The department will perform specialised techniques to help diagnose Fanconi anaemia (FA), Ataxia telangiectasia (AT) and Bloom's syndrome.

FA and AT need an age and sex matched control and therefore prior notice of requesting these tests is desirable. Due to the culture timing that is required, it is necessary for such samples to be processed on a Monday or Tuesday.

For adults and children a minimum of 5mL of whole blood (babies - minimum of 2mL) in a lithium heparin tube. Mix thoroughly. Do not spin. Blood should be kept cool but not frozen in transit.

The request form should be completed with name and date of birth of patient, comprehensive clinical details, specific test requirements, and a legible name and contact details for the referring practitioner.

As all of these tests are labour intensive, it is approximately 10-14 days before any results are issued.

Costs

The cost of all of the above diagnostic cytogenetics for Australian patients varies according to the particular testing requested, but in most instances, attracts a Medicare rebate.

Overseas patients will also be charged according to the actual testing required.

Subtelomeric FISH testing

Subtelomeric FISH analysis is a new test able to detect minute alterations at the tips of human chromosomes. Most subtelomere rearrangements are not visible under normal light microscopic examination. This test can detect a chromosome abnormality in a further 3-5% of patients with unexplained developmental delay ± dysmorphic features.

Subtelomeric testing requested by a medical practitioner costs $200/patient in addition to the normal cost of chromosome analysis. The patient will receive a separate account for $200 for which there will be no medicare rebate. Subtelomere testing is available free of charge for a small number of hospital patients selected by the South Australian Clinical Genetics Service .

Specimen requirements

Subtelomeric testing will only be performed subsequent to normal cytogenetic analysis. See previous requirements.

Limitations of Test

Mosaicism can not be excluded. Generally 20 cells are examined. This allows for 14% mosaicism to be excluded with 95% confidence limits.

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