Intermediate allele predictive test result

An ‘intermediate allele’ gene has between 27-35 CAG repeats. Individuals with an intermediate gene will not develop HD. However, the number of CAG repeats in an intermediate gene can be unstable when passed to the next generation. As a result of this instability, the number of CAG repeats may increase beyond the number required for HD (i.e. 36 or greater) when passed from parent to child. Consequently, children have an increased risk of developing HD in later life. CAG repeats are most unstable when a father transmits the intermediate gene; the number of CAG repeats usually remains stable when a mother transmits the gene. The chance that the number of CAG repeats may increase into the HD range is thought to be small and current research is examining the magnitude of risk in greater detail.