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FRAGILE X SYNDROME

Background

Fragile X syndrome (OMIM 300624) is characterised by moderate to severe mental retardation, macroorchidism and distinct facial features which include a long face, large ears and prominent jaw. Fragile X sydrome is caused by the expansion of a CGG repeat in the FMR1 gene and abnormal methylation of the gene. Premutations of FMR1 do not cause mental retardation but are associated with premature ovarian failure in females and late onset tremor/ataxia syndrome in males. Premutations are unstable and, when transmitted by a female, have a risk of expanding to a full mutation. Alleles within the intermediate size range are not thought to be associated with developmental delay/learning disability but may display size instability in future generations.
 

Testing at WRGL

A fluorescent triplet-primed PCR-based assay is used to determine the size of the CGG repeat in the FMR1 gene. Prenatal analysis can be performed – please notify the laboratory if this is required.
 
The CGG repeat range definitions used in this laboratory are those defined by the European Molecular Genetics Quality Network (EMQN) and are shown in the following table.

 

CGG Repeat Number

Definition

<45 Normal
45-54 Intermediate
55-200 Premutation
>200 with abnormal methylation Full mutation

 

Cost, Sample Requirements & Turnaround Times

 

Test

Cost NZD*

Sample Requirements

Current TAT

Fragile X PCR $220 4 ml of whole blood in EDTA (purple top) 1-2 weeks
Prenatal
Fragile X PCR
$220 + cost of excluding maternal cell contamination (MCC) 4 ml of whole blood in EDTA (purple top) from mother,
CVS 20-30 mg
clean villi

up to 1 week

 
*No direct charge for the central region DHBs covered by the Crown Funding Agreement


 

Fragile X

ABOUT US

Wellington Regional Genetics Laboratory (WRGL) provides a comprehensive, integrated diagnostic cytogenetic and molecular genetic testing service

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CONTACT US

(04) 918-5352
wrgl@ccdhb.org.nz