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MOLECULAR Analysis:
FMR1 Related Disorders (FXTAS, POF)
The CGG trinucleotide repeat in the fragile X gene (FMR-1) is variable in length. Normal individuals have from 5 to 44 repeats. Unaffected carriers of a fragile X mutation have what is termed a premutation. These individuals have from 55 to 200 trinucleotide repeats. In patients with fragile X syndrome, the premutation has expanded to greater than 200 repeats. Expansions in this range are termed full mutations and result in complete disruption of the FMR-1 gene. A gray zone repeat range exists from 45 to 54 repeats. Repeat numbers in this range have been shown to be stable in some families and unstable in others.
Fragile X Associated Tremor/Ataxia Syndrome (FXTAS) is a progressive neurodegenerative disorder primarily affecting fragile X premutation carrier males over age 50. The penetrance of FXTAS increases with age.
Females with premutations are at increased risk for premature ovarian failure or ovarian dysfunction.
- Individuals with a diagnosis of FXTAS
- Females with premature ovarian failure or ovarian dysfunction
Direct mutation analysis: Our testing methodology incorporates polymerase chain reaction (PCR) and Southern blot technologies. Fluorescent labeled primers are used to amplify the CGG repeat region in the FMR1 gene. PCR is followed by capillary electrophoresis on the ABI 3130 Genetic Analyzer. PCR analysis is useful in determining repeat numbers in the normal and premutation ranges. Southern analysis with the probe pE5.1 detects full expansions of the CGG trinucleotide repeat.
FXTAS occurs in approximately 20 to 30% of fragile X premutation carrier males. Individual cases of carrier females with FXTAS have been reported. Premature ovarian failure occurs in approximately 20% of females who have an FMR1 premutation.
Blood: 5 cc collected in a purple top (EDTA) or yellow top (acid citrate dextrose) vacutainer tube. Do not centrifuge or freeze. Sample may be refrigerated or stored at room temperature.
Please contact the laboratory at 858-534-3093 for information on prenatal testing.
14 days
PCR: 83890, 83894, 83900, 83901, 83909 (2X), 83912
For PCR and Southern blot add 83892, 83896, 83897
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