A “negative” predictive test result means that the individual has not inherited the DNA change associated with HD:
This individual will not develop HD.
- The number of CAG repeats on both genes contain 26 or fewer CAG repeats
- The accuracy of this result is almost 100% if a parent or other affected relative is shown to have a CAG size in the HD range (i.e. 36 CAG repeats or more)
- Rarely, a person can appear to have physical signs of HD yet both of their genes have a CAG size in the normal. These rare cases requires further medical investigations to determine the individual’s diagnosis.