Demand for predictive genetic testing for Huntington's disease in Australia, 1987 to 1993

Genetic counseling and testing for Huntington's disease: A historical review

This manuscript describes the ways in which genetic counseling has evolved since John Pearson and Sheldon Reed first promoted "a genetic education" in the 1950s as a voluntary, non-directive clinical tool for permitting individual decision making. It reviews how the emergence of Huntington's disease (HD) registries and patient support organizations, genetic testing, and the discovery of a disease-causing CAG repeat expansion changed the contours of genetic counseling for families with HD. It also reviews the guidelines, outcomes, ethical and laboratory challenges, and uptake of predictive, prenatal, and preimplantation testing, and it casts a vision for how clinicians can better make use of genetic counseling to reach a broader pool of families that may be affected by HD and to ensure that genetic counseling is associated with the best levels of care. © 2016 Wiley Periodicals, Inc.

Problems assessing uptake of Huntington disease predictive testing and a proposed solution

The uptake of predictive testing for Huntington disease informs our understanding of decision making by those at risk and assists with planning for service provision. Uptake figures have been reported from several centers based on the total number of people who have undertaken predictive testing as a percentage of those estimated to be at 50% risk in the region. This method produced a figure of 35% from our own service, much higher than observation of the local pedigrees indicated, and higher than other published reports. We have identified some errors in the commonly used formula. The major errors are the use of the cumulative total of those who have had testing with a static denominator of those at 50% risk, and the failure to exclude from the at-risk group those who are too young and therefore ineligible to test.We report data from the Huntington Disease Register of Victoria and estimate the prevalence to be 8 per 100,000 in 1999. Additional data on individuals at risk were collated. We found that for every diagnosed person there were 4.2 individuals at 50% risk, a lower ratio than one to five hypothesized in the literature. We examined these ratios in the context of uptake.Significantly, we provide a solution to the calculation of uptake with a formula that factors in a dynamic denominator and corrects for the number of years testing has been offered. Using this formula, we calculated an uptake of 13.0-15.4% for the state of Victoria, Australia. This formula can be used to compare uptake across different centers.

Predictive testing for Huntington's disease

Worldwide, predictive testing for Huntington's disease has become an accepted clinical application that has allowed many individuals from HD-families to proceed with their life without the uncertainty of being at risk. International guidelines have extensively contributed to establishing counselling programmes of high quality, and have served as a model for other genetic disorders. Psychological follow-up studies have increased the insight into the far-reaching impact of test results for all individuals involved. Although the guidelines have served as a useful frame of reference, clinical experience has shown the importance of a case-by-case approach to do justice to the specific needs of the individual test candidate. Issues such as ambiguous test results, lack of awareness in a test candidate of early signs of the disease, non-compliance to the test protocol, or the test candidate's need for information on the relationship between age at onset and CAG-repeat require careful consideration. Receiving a test result is only one of the transition points in the life of an individual at risk; such result needs to be valued from a life-cycle perspective.

Fifteen years of experience in predictive testing for Huntington disease at a single testing center in Victoria, Australia

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.

Reproductive decision making before and after predictive testing for Huntington's disease: an Australian perspective

A retrospective study examined both pre- and post-result reproductive decision making for 281 people at risk for Huntington's disease aged 18-45 years who had undergone predictive testing in one centre in Australia between 1990 and 2002. Forty-eight per cent of subjects had one or more pre-result pregnancies, and of these, three had prenatal linkage testing. One high-risk (50%) pregnancy was terminated. Four couples chose an alternative reproductive option. Following testing, data were available for 231 subjects, and no significant difference was found between mutation carriers and non-carriers in the occurrence of post-result pregnancies. This contrasts with the finding of a recent European study, although the outcome of the present study may have been influenced by loss of follow-up data for 50 subjects. Five carriers (17%) had a total of six prenatal tests. Four showed a carrier result and these pregnancies were terminated. Two carriers utilized an alternative reproductive option (donor insemination and pre-implantation genetic diagnosis). The results of this study confirm previous findings of a low uptake of prenatal testing and alternative reproductive options by people at risk for Huntington's disease undergoing predictive testing.

Gender Differences in Attitudes Among Those at Risk for Huntington's Disease

This report presents and discusses selected findings regarding gender differences from an Australian-based study that investigated attitudes of individuals at risk for Huntington's disease (HD) towards genetic risk and predictive testing. Clear gender differences emerged regarding perceived coping capacity with regard to predictive testing, as well as disclosure of the genetic risk for HD to others. Female participants were more likely to disclose their genetic risk to others, including their medical practitioners, while male participants were three times more fearful of disclosing their genetic risk to others. These findings are of interest in light of gender differences that have consistently been reported regarding the uptake of predictive testing for HD, other genetic conditions, and health services more generally. While gender differences cannot provide a fully explanatory framework for differential uptake of predictive genetic testing, men and women may experience and respond differently to the genetic risk for HD and possibly other inherited disorders. The meanings of genetic risk to men and women warrants further exploration, given anticipated increases in genetic testing for more common conditions, especially if post-test interventions are possible. These issues are also relevant within the context of individuals' concerns about the potential for discrimination on the basis of genetic risk or genetic test information.

Genetic testing for Alzheimer's disease

Genetic factors are important in the development of Alzheimer's disease (AD). Familial AD can result from rare mutations in some genes. Other genes, such as the apolipoprotein E gene (APOE), operate as risk factors for late-onset sporadic AD. On a background of advances in the genetics of AD we suggest a way in which genetic information may be used in the diagnosis of AD. If there is a positive family history of early-onset dementia and the clinical features suggest AD, patients may be tested for presenilin and amyloid precursor protein gene mutations with appropriate pretest and post-test counselling. Predictive testing should be performed under guidelines developed by the World Federation of Neurology and the Human Genetics Society of Australasia. The usefulness of APOE genotyping as an adjunct to conventional diagnostic tests is unknown; data suggest it has low sensitivity and specificity and may have little predictive value in an individual patient. APOE genotyping should not be performed in asymptomatic individuals, except as part of an ethically approved research project; this recommendation is supported by a number of international consensus statements. APOE testing should not be used as a diagnostic test without adequate pretest and post-test counselling, education and support. APOE testing should not be used as a sole diagnostic test in the work-up of patients with AD. Genetic risk factors other than APOE require validation and should not be used routinely, except as part of an ethically approved research protocol.