Fragile X Syndrome: FMR1 Triplet Repeat Analysis

Diagnostic Use

The classic fragile X syndrome phenotype is male mental retardation to varying degrees, mild dysmorphic (abnormal-appearing) features, and enlargement of the testes in adults. Female heterozygotes may also be affected, depending on the pattern of X-inactivation in the brain.

Department

Genetics - Molecular Pathology

Delphic Registration Code

MOLP

Synonyms

FMR1 CGG repeat
FXTAS
POF
Premature ovarian failure

Turnaround Time

4 weeks

Test Code

5138

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

4.0

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

1.0

Minimum Sample Volume (ml)

0.5

Additional Specimen Information

This genetic analysis requires nucleated cells. Please don’t centrifuge or freeze the EDTA blood tube.

Aliquot Instructions

Sample Type

• Whole Blood

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

This genetic analysis requires nucleated cells. Please don’t centrifuge or freeze the EDTA blood tube.

If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Analysis and interpretation of this assay requires knowledge of the biological sex of the patient being tested. Please assist us in delivering quality results by providing accurate biological sex information on all referrals for this testing.

Interpretation

CGG repeats of normal, intermediate and low premutation size are amplified in the standard PCR. Normal males are identified by the presence of an allele with less than 58 CGG repeats. Premutations up to about 90 repeats are detectable. Females heterozygous for two normal alleles are also identified however about one-third of normal females are homozygous and are indistinguishable from fragile-X carriers in the standard PCR assay. These females, as well as the minority of samples which fail to amplify are re-analysed by triplet repeat primed PCR (TP-PCR) which reliably detects expanded CGG repeats in the 100 to >1000 repeat range but does not determine
repeat number.

Reference Intervals

Test Method

Fluorescently tagged PCR fragments from the FMR1 CGG repeat region at Xq27.3 are accurately sized on the ABI3130xl Genetic Analyser. Triplet repeat primed PCR (TP-PCR) may be employed in some cases to detect large CGG expansions.

Non-Funded Test Cost

$234.56 (Exclusive of GST)

Billing Code

5138

Uncertainty of Measurement:
The PCR assay has an uncertainty of measurement of one repeat unit within the normal and intermediate size ranges, verified by testing the NIST fragile X Standard Reference Material PN2399.

Contact Information

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