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C9ORF72 Repeat Expansion (New test)

Item Value
Approval req'd? No
Available Stat? No
Test code ALSC9
Performed by Molecular Diagnositcs
In House Availability Run once per month
Method PCR and Southern blot
Collection Instructions Do not collect sample in heparin. Avoid hemolysis. Keep sample refrigerated for overnight or longer storage. Do not freeze.
Container type Lavender top
Amount to Collect 5 mL blood
Sample type EDTA whole blood, amniotic fluid, CVS; cultured cells

Note: Amniotic fluid and CVS collected at UCSF will be sent to Cytogenetics for culturing prior to testing. The tissue culture will be separately billed
Preferred volume
Peripheral blood in EDTA 5 mL
Amniotic fluid 20 mL
CVS 20 mg
Cultured cells from non-UCSF sites T25 flask x2


Note: Amniotic fluid and CVS collected at UCSF will be sent to Cytogenetics for culturing prior to testing. The tissue culture will be separately billed
Min. Volume
Peripheral blood in EDTA 2 mL
Amniotic fluid 10 mL
CVS 10 mg
Cultured cells T25 flask x1
UCSF Rejection Criteria Heparinized samples. Low confluence cell cultures. Insufficient amount of amniotic fluid or chorionic villi
Processing notes Do not centrifuge or freeze. Ship at room temp or 4C. Refrigerate samples for storage.
Normal range Negative for the hexanucleotide repeat expansion (1-30 repeats)
Synonyms FTD/ALS Hexanucleotide Repeat Expansion; Frontotemporal Dimentia; Amyotropic lateral Sclerosis
Stability Room temperature 3 days, refrigerated 1 week.
Turn around times 4-6 weeks
Reflex? Positive expansions are reflexed to a Southern blot based-assay that will determine the approximate ranges of the expanded repeat.
Additional information An interpretation of this test by a laboratory physician will automatically be performed and billed for separately.

Amyotrophic lateral sclerosis (ALS) and fronototemporal dementia (FTD) are neurodegenerative disorders characterized by progressive paralysis and cognitive decline, respectively. Although most of ALS and FTD cases are sporadic and idiopathic, approximately 5 – 10% of affected individuals follow a Mendelian pattern of an autosomal dominant inheritance. A hexanucleotide repeat (GGGGCC) located in the promoter region of the C9orf72 gene is strongly associated with familial cases of ALS and/or FTD and thus constitutes the basis of the present molecular diagnostic assay. Pathologic expansions (>30 repeats) can be used for the presymptomatic or symptomatic diagnosis of these disorders. Other mutations that casuse ALS and/or FTD occur in the superoxide dismutase (SOD), RNA binding protein FUS (Fused in Sarcoma) and the transcriptional repressor TDP-43 genes. None of these mutations are covered by this assay.

The C9orf72 hexanucleotide repeat in negative individuals consists of up to 30 repeats. In most affected individuals, the repeat was shown to expand to 250-1600 repeats or more. The pathogenic expansions was found to be non-penetrant in carriers who were younger than 35 years of age, increasing to 50% penetrance by 58 years and to almost full penetrance by 80 years. There is also evidence of genetic anticipation in families segregating the pathogenic repeat showing an earlier age of onset in subsequent generations.

This test consists of two PCR assays that will detect first, the repeat size on alleles within the negative range of 1-30 repeats and second, the presence or absence of a positive expanded repeat. Positive expansions are reflexed to a Southern blot based-assay that will determine the approximate ranges of the expanded repeat.

Evidence of genetic counseling should be provided for any presymptomatic testing.

This test was developed and its performance characteristics determined by the UCSF Clinical Laboratories. It has not been cleared or approved by the Food and Drug Administration. The FDA has determined that such clearance or approval is not necessary. This test is used for clinical purposes. It should not be regarded as investigational or for research. This laboratory is certified under the Clinical Laboratory Improvement Amendments of 1988 (CLIA-88) as qualified to perform high complexity clinical laboratory testing.
CPT coding 81479
LDT or Mod FDA? Yes
Last Updated 9/10/2013 9:07:57 AM
Entry Number 1544

If you have additional questions regarding this test, please call: 415-353-1667

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