In patients who have the cytogenetic changes of fragile X syndrome but lack the molecular changes characteristic of that disorder (i.e., are FMR1-mutation negative), a second site of fragility, symbolized FRAXE, has been demonstrated to be expanded. Data suggests that an etiologic relationship may exist between FRAXE and nonspecific X-linked intellectual disability. Loss of expression of the gene AFF2, also known as FMR2, has been correlated with FRAXE expansion. Sequence analysis and deletion/duplication analysis are available to identify mutations in the AFF2 gene.
For patients with suspected FRAXE syndrome, repeat expansion testing and methylation analysis in males and repeat expansion testing only in females are recommended as the first step in mutation identification. For patients in whom mutations are not identified, full gene sequencing and deletion/duplication analysis are also available.
This test is indicated for:
- Confirmation of a clinical diagnosis of FRAXE syndrome
- Carrier testing in adult females with a family history of FRAXE syndrome
Detection and Reference Range
All cases of FRAXE syndrome caused by CCG expansion of the AFF2 gene will be detected by this assay. Rare cases of FRAXE syndrome caused by mutation of the AFF2 gene will not be detected by this assay.
Normal: Approximately 6-35 CCG repeats. Affected: Approximately >200 CCG repeats.
Type: Whole Blood
Specimen Requirements:In EDTA (purple top) or ACD (yellow top) tube:
Infants (<2 years): 2-3 ml
Children (>2 years): 3-5 ml
Older Children & Adults: 5-10 ml
Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.
- Full gene sequencing and deletion/duplication analysis of the AFF2 gene is available for those individuals in whom repeat analysis and methylation testing is negative.
- Testing for fragile X syndrome at the FRAXA site is available by repeat expansion/methylation analysis, FMR1 sequencing, and FMR1 deletion/duplication analysis.