Eurofins Biomnis code

XFRA

Synonyms

• OMIM code : #300624 /*309550
• FMR1

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.

Prenalytics

• 5 mL
• Whole blood EDTA (only), do not use tubes containing beads.
• Ambient temperature

Further information

• Attach the clinical data
• Sample must be refrigerated if transport is > 48 hours
• According to regulation, each request must ALWAYS be accompanied by a consent form signed by the patient and the prescribing pathologist
• 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