Huntington Disease: CAG Repeat Analysis
Test Code: 6942
Turnaround time: 3 weeks
Huntington disease is a progressive neurodegenerative disease characterized by chorea and dementia. This disease is inherited in an autosomal dominant fashion and affects approximately 1 per 10,000 individuals. Although patients may develop symptoms at any time from childhood to later in life, the average age of onset is between 35 and 45. With paternal transmission of the gene, there is a tendency for earlier onset to occur. Over 80% of the patients with an onset before the age of 20 inherited the abnormal gene from their father. Mutations may occur spontaneously as well, but this is uncommon.
Huntington disease is caused by an abnormal expansion of a CAG repeat within the HTT/ITI5 on chromosome 4. Although the number of CAG repeats correlates with the age of onset, the correlation is not precise enough to use in determining disease prognosis for an individual patient.
Due to the complexities and ethical issues surrounding genetic testing for Huntington, a signed consent form for Huntington disease testing is mandatory.
This test is indicated for:
- Confirmation of a clinical diagnosis of Huntington disease
- Presymptomatic testing in adults with a family history of Huntington disease
CAG repeat number is determined by PCR amplification and fragment size analysis.
Nearly 100% of CAG expansions in the HTT/ITI5 gene will be detected by this assay.
Normal individuals have 6-35 repeats while individuals with greater than 39 CAG repeats have a high probability of developing the disease. When the repeat number is between 36 and 39, Huntington disease cannot be reliably diagnosed due to incomplete penetrance.
Type: Whole Blood
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml
Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.
A signed consent form for Huntington disease testing is mandatory.