Tests Included

If only one allele is detected by PCR, then a second PCR-based assay will be performed to determine if there is a second allele with an expanded CAG repeat. An additional Southern blot analysis should be considered for those specimens with a negative result on the reflexed assay.

Performed

Monday - Friday

Methodology

Polymerase Chain Reaction / Fragment Analysis

Reported

Routine: 12 - 14 days

Synonyms

  • Huntington's Disease
  • Huntington's Chorea
  • Huntingtin Gene
  • HTT Gene
  • Clinical Genomics

Performing Lab

Clinical Genomics

Turnaround Time

14 days

Add-on Eligibility

Yes, within 7 days of collection
*If DNA has been extracted previously for other Clinical Genomics tests, this is stored for 6 weeks and may qualify for add-on

Specimen Type

Blood

Specimen Volume

5 mL (Minimum: 1 mL)

Collection Container

EDTA Whole Blood Tube (Lavender Top Vacutainer)

Unacceptable Conditions

  1. Severely clotted or grossly hemolyzed specimens
  2. Specimens that have been improperly collected, stored, or transported
  • Specimens collected in preservatives other than EDTA
    • ACD tubes are accepted, but EDTA is preferred
  • Serum or plasma
  • Specimens that have been frozen
  • Commingled specimens
  1. Specimens in tubes that have been damaged or broken during transport
  2. Specimens with insufficient volume for testing
  3. Unlabeled or mislabeled specimens

Storage/Transport Temperature

Transport Instructions      
Collection Location Transport Temperature Processing Required Timeframe
ED/Inpatient Room Temperature None Specimen must be received by the lab within 3 days of collection
Laboratory/Outpatient/Off-Site Room Temperature None Specimen must be received by the lab within 3 days of collection

Storage: Refrigerated

Stability (from collection to initiation)

Stability:
Prior to Extraction:
  • Room Temperature: 3 days
  • Refrigerated: 7 days
  • Frozen: Unacceptable
Extracted DNA:
  • Room Temperature: Unacceptable
  • Refrigerated: Unacceptable
  • Frozen: Indefinitely

Laboratory Storage: 
  • Original Specimen: Refrigerated
  • Extracted DNA: Frozen
Laboratory Retention: 
  • Original Specimen: 6 weeks
  • Extracted DNA: 6 weeks

Collection Instructions

Labeling Instructions:
When labeling blood tubes, leave a small window visible for the lab to assess the fill volume and sample integrity. Ensure that the barcode is in the correct orientation.


Collection Instructions:
Follow the correct order of draw when collecting with additional orders and tube types:
     
 

Reference Interval

Negative: ≤ 26 CAG repeats

Interpretive Data

Huntington Disease is a neurodegenerative disorder causing progressive cognitive, motor, and psychiatric disturbances typically beginning at 35-44 years of age (although 5% are affected as juveniles and 25% are affected after age 50). HD is caused by an expansion of a trinucleotide (CAG) repeat region within the first exon of the HTT gene (c.52CAG), leading to the production of an abnormal protein product.

Incidence: 1 in 10,000

Inheritance: Autosomal Dominant

Cause: Expanded number of CAG repeats in the HD gene
  • Unaffected, Mutable: 27 - 35 repeats
  • Reduced Penetrance: 36 - 39 repeats
  • Affected, Full Penetrance: ≥ 40 repeats

Clinical Sensitivity and Specificity: 99%

Methodology: PCR followed by size analysis using capillary electrophoresis; all apparent homozygotes reflexed to a second, alternatively primed PCR analysis

Analytical Sensitivity and Specificity: 99%

Limitations: Other neurodegenerative disorders will not be detected. Diagnostic error may occur with this test due to rare genetic variation at a primer binding site. PCR-based methodologies have detected trinucleotide expansions up to approximately 115 CAG repeats; alleles with expansions greater than 115 repeats may be undetectable by PCR.

This test was developed and its performance characterictics determined by the UC San Diego Health System Molecular Diagnostics Laboratory. It has not been cleared or approved by the US Food and Drug Administration. FDA clearance or approval is not required for clinical use. The result of this test should be interpreted using all relevant clinical data and should not be used alone for clinical diagnosis or patient management decisions.
Ordering

Tests Included

If only one allele is detected by PCR, then a second PCR-based assay will be performed to determine if there is a second allele with an expanded CAG repeat. An additional Southern blot analysis should be considered for those specimens with a negative result on the reflexed assay.

Performed

Monday - Friday

Methodology

Polymerase Chain Reaction / Fragment Analysis

Reported

Routine: 12 - 14 days

Synonyms

  • Huntington's Disease
  • Huntington's Chorea
  • Huntingtin Gene
  • HTT Gene
  • Clinical Genomics

Performing Lab

Clinical Genomics

Turnaround Time

14 days

Add-on Eligibility

Yes, within 7 days of collection
*If DNA has been extracted previously for other Clinical Genomics tests, this is stored for 6 weeks and may qualify for add-on
Collection

Specimen Type

Blood

Specimen Volume

5 mL (Minimum: 1 mL)

Collection Container

EDTA Whole Blood Tube (Lavender Top Vacutainer)

Unacceptable Conditions

  1. Severely clotted or grossly hemolyzed specimens
  2. Specimens that have been improperly collected, stored, or transported
  • Specimens collected in preservatives other than EDTA
    • ACD tubes are accepted, but EDTA is preferred
  • Serum or plasma
  • Specimens that have been frozen
  • Commingled specimens
  1. Specimens in tubes that have been damaged or broken during transport
  2. Specimens with insufficient volume for testing
  3. Unlabeled or mislabeled specimens

Storage/Transport Temperature

Transport Instructions      
Collection Location Transport Temperature Processing Required Timeframe
ED/Inpatient Room Temperature None Specimen must be received by the lab within 3 days of collection
Laboratory/Outpatient/Off-Site Room Temperature None Specimen must be received by the lab within 3 days of collection

Storage: Refrigerated

Stability (from collection to initiation)

Stability:
Prior to Extraction:
  • Room Temperature: 3 days
  • Refrigerated: 7 days
  • Frozen: Unacceptable
Extracted DNA:
  • Room Temperature: Unacceptable
  • Refrigerated: Unacceptable
  • Frozen: Indefinitely

Laboratory Storage: 
  • Original Specimen: Refrigerated
  • Extracted DNA: Frozen
Laboratory Retention: 
  • Original Specimen: 6 weeks
  • Extracted DNA: 6 weeks

Collection Instructions

Labeling Instructions:
When labeling blood tubes, leave a small window visible for the lab to assess the fill volume and sample integrity. Ensure that the barcode is in the correct orientation.


Collection Instructions:
Follow the correct order of draw when collecting with additional orders and tube types:
     
 
Result Interpretation

Reference Interval

Negative: ≤ 26 CAG repeats

Interpretive Data

Huntington Disease is a neurodegenerative disorder causing progressive cognitive, motor, and psychiatric disturbances typically beginning at 35-44 years of age (although 5% are affected as juveniles and 25% are affected after age 50). HD is caused by an expansion of a trinucleotide (CAG) repeat region within the first exon of the HTT gene (c.52CAG), leading to the production of an abnormal protein product.

Incidence: 1 in 10,000

Inheritance: Autosomal Dominant

Cause: Expanded number of CAG repeats in the HD gene
  • Unaffected, Mutable: 27 - 35 repeats
  • Reduced Penetrance: 36 - 39 repeats
  • Affected, Full Penetrance: ≥ 40 repeats

Clinical Sensitivity and Specificity: 99%

Methodology: PCR followed by size analysis using capillary electrophoresis; all apparent homozygotes reflexed to a second, alternatively primed PCR analysis

Analytical Sensitivity and Specificity: 99%

Limitations: Other neurodegenerative disorders will not be detected. Diagnostic error may occur with this test due to rare genetic variation at a primer binding site. PCR-based methodologies have detected trinucleotide expansions up to approximately 115 CAG repeats; alleles with expansions greater than 115 repeats may be undetectable by PCR.

This test was developed and its performance characterictics determined by the UC San Diego Health System Molecular Diagnostics Laboratory. It has not been cleared or approved by the US Food and Drug Administration. FDA clearance or approval is not required for clinical use. The result of this test should be interpreted using all relevant clinical data and should not be used alone for clinical diagnosis or patient management decisions.

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