Huntington disease testing

Last updated: Wednesday, 11, March, 2009

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Item Process
Specimen

10-20 mL blood in EDTA tube.

Method

PCR analysis to detect an expanded triplet repeat mutation in the Huntington gene.

Application

Used to detect the Huntington disease mutation in symptomatic or asymptomatic people.

Predictive tests in asymptomatic family members should only be arranged after consultation with the pathologist and a clinical genetics service.

Prenatal diagnosis is available.

The DNA test may also be used to assist in the differential diagnosis of a neurological problem which could be Huntington disease.

Interpretation

In the normal population the triplet repeat region is less than 31 triplets in length whilst those with Huntington disease have repeats which are >37.

The identification of the characteristic expansion of the triplet repeat is diagnostic for the presence of the Huntington disease mutation. Those with very high repeat numbers eg, >50 repeats typically have early onset of disease.

Individuals with triplet repeats between 31-37 are thought to have a premutation and although they may not develop Huntington disease, their offspring may be at risk.

Care should be taken in interpreting the normal and pathological range for triplet repeats since there is some variability between laboratories. Similarly, the significance of the repeat numbers may be interpreted differently in some cases.

Reference

Rubinsztein DC et al. Am J Hum Genet 1996; 59: 16-22.

ACMG/ASHG. Am J Hum Genet 1998; 62: 1243-1247.