Table 2.

General HD information to include in genetic counseling

Explanation of autosomal-dominant inheritance and risk to the patient, relatives, and children

Description of DNA, the CAG expansion in HTT, and how the expansion produces a toxic protein that causes HD

Explanation of the four repeat ranges that can be seen in a test result: ≤26 = normal, 27–35 = intermediate–normal phenotype but expandable, 36–39 = reduced penetrance and expandable, ≥40 fully penetrant

Reverse correlation between age of onset and number of repeats

Anticipation (usually through the paternal line) and the possibility of juvenile HD