Eurofins Biomnis code

XFRAP

Synonyms

• OMIM code : #300624 / *309550

Clinic significance

Fragile X syndrome is the most common cause of hereditary mental retardation and accounts for 40% of all X-linked mental retardation. The disease affects about 1/1500 boys and 1/2500 girls, with very variable symptomatology, especially in girls. The mutation consists of an increase in the number of CGG repeats in exon 1 of the FMR-1 gene at Xq27.3 which is accompanied by local methylation and under-expression of the gene product. This region of the chromosome is unstable and the mutation can develop progressively and three stages are recognised:

- normal subjects have fewer than 50 CGG repeats;
- predisposed but healthy subjects have between 50 and 200 CGG repeats but the region is not methylated;
- affected subjects have over 200 CGG repeats and the region is methylated.

The phenotype of predisposed women is normal (no mental retardation) but their children may be affected (the risk is proportional to the number of repeats). Predisposed women should be offered the possibility of prenatal diagnosis.
Preconception screening and prenuptial screening are not authorized in France, any request received for this reason will be cancelled.

Prenalytics

• Fresh or cultured amniotic fluid, fresh or cultured trophoblast
• Ambient temperature

Further information

• 5 ml of whole blood on EDTA from each parent (quotation on request) is required to perform this test
• ALWAYS attach the medical prescription, the clinical patient's history and the consent form signed by both the patient and the prescribing clinical
• Enclose the specific B12-INTGB request form: Molecular Genetics

Documents to download

• Specific Request Form (B12-INTGB)

Methodology

PCR - PCR Amplidex (confirmation)

Turnaround time

9 days PCR - 15 days for confirmation by Amplidex PCR