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Paediatric Laboratory Medicine

Fragile X E Syndrome: FMR2 Trinucleotide Repeat Analysis

Clinical Significance

FRAXE is a form of non-syndromic X-linked intellectual disability characterized by mild intellectual disability. The FRAXE phenotype is quite variable, and tends to include slow learning, hyperactivity, attention problems and language delay. The gene associated with FRAXE is called FMR2. The normal gene contains a three base pair sequence, which is repeated on each X chromosome (called a CCG repeat). The principal mutation causing FRAXE is an expansion of the CCG repeat sequence within the FMR-2 gene.

Test Name

Fragile X E Syndrome: FMR2 Trinucleotide Repeat Analysis

Alternate Name/ Synonym

FRAXE syndrome

Gene Name

  • FMR2

Alternate Gene Name


Test Code



Molecular Genetics


FMR2 5'UTR trinucleotide (CCG) repeat analysis via PCR

External Proficiency Testing


Turn Around Time

2 weeks (Prenatal samples), 2-3 weeks (Pregnancy/Urgent samples), 4-6 weeks (Routine)


AF4/FMR2 family, member 2


Fragile X E Syndrome

Specimen Type

Blood; gDNA.

For details about specimen requirements, please refer to: Specimen Type & Requirements (PDF).

Minimum Specimen Requirements

5-10 mL EDTA or ACD 0.5 mL EDTA (neonate); minimum 10 ug in 100 uL low TE (pH8.0)


Room Temperature

Special Requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

The eligibility for this test is determined by the presence of a family history suggestive of X-linked intellectual disability; a pedigree must be provided for Fragile X E testing.

Approval is required

CPT Codes


Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Phone: 416-813-7200
Phone: 1-855-381-3212


Interpretation is provided in report

Information Sheet: Fragile X E Syndrome