Tests
1st tests to order
no initial tests
Test
Result
diagnosis is clinical
Tests to consider
CAG repeat testing
Test
Ordered in patients to confirm a clinical diagnosis of Huntington disease.
Can be deferred until a time of the patient's choosing.
A positive result indicates, with virtual certainty, that the patient will develop symptoms of Huntington disease during a normal lifespan.
An intermediate result of 36 to 39 repeats implies that the person may or may not develop symptoms of Huntington disease during their lifetime.
A result of 29 to 35 repeats represents an expanded CAG repeat that will not result in disease in the patient, but is within a range that could expand sufficiently to result in disease in offspring.[10]
Less than 28 repeats is a normal result.
If the test is normal, further tests to identify other causes for symptoms are required.
Result
a positive result is ≥40 CAG repeats on 1 of the 2 alleles; an intermediate result is 36 to 39 repeats
MRI or CT scan
Test
Caudate or striatal atrophy is often not definitively present in very early Huntington disease.
Caudate or striatal atrophy is not specific as it can be seen in disorders other than Huntington disease (e.g., neuroacanthocytosis).[18]
Result
evident caudate or striatal atrophy may be apparent
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