Purpose: This retrospective study describes 15 years of experience in predictive testing for Huntington disease at a single center in Victoria, Australia.
Method: Data collected on 756 participants included age, gender, family history, prior risk and the age at which this risk became known, exposure to Huntington disease, number of children, and proximity to the testing center.
Results: Some 57.8% of participants were female, and 88.8% had a 50% risk of developing Huntington disease. The mean age at entry was 40.4 years and was gender-independent. Of all completed tests (n = 648), 37.5% gave high-risk results, and 3.2% were in the zone of reduced penetrance. The 14.3% who withdrew from testing tended to be younger and childless, lacked exposure to severe Huntington disease, and more often at 25% or less risk. Some 32.4% of candidates presented for testing within 1 year of becoming aware of their risk, and most of these individuals had little or no exposure to severe Huntington disease. Those whose exposure was considerable waited on average for more than 13 years. Among the most inexperienced candidates were a group of "adoptees" (raised away from their biological family). Maternal transmission was the source of risk for 19 of 20 adoptees.
Conclusion: This study illustrates the significance of exposure to Huntington disease and its impact on the timing of testing.