The difficulties that may arise in deciding upon a protocol to employ, should presymptomatic testing for vCJD become available, have been acknowledged.30 However, a detailed examination of possible protocols and a thorough analysis of the benefits and harms are yet to be undertaken. There is an urgent need to consider these issues prior to the availability of such a test. While the public health benefits of offering such a test are significant, so too is the risk of harm to individuals if testing is administered incorrectly.
COMPARISONS WITH PREDICTIVE GENETIC TESTING FOR HUNTINGTON’S DISEASE
Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder. It has a mean age of onset of 37 years and no effective treatment is available. On average, HD results in death 15 years after symptom onset.38 Presymptomatic genetic testing for HD has been available since 1986. This is generally undertaken in the setting of a formalised protocol whereby, prior to genotyping, those at risk have the opportunity to explore issues around what a positive result and a negative result may mean for them and their family.39 An exemplary protocol is outlined in guidelines developed by the International Huntington Association and the World Federation of Neurology.40
The majority of those at risk of developing HD choose not to have presymptomatic testing41 and guidelines advise against testing anyone under the age of 18 years.40 In a study of the outcomes of presymptomatic testing for HD it was found that 2% of individuals who received a positive result for a causative HD mutation experienced a catastrophic event (defined as committing suicide, attempting suicide, or requiring psychiatric hospitalisation).42 This rate of catastrophic events has been interpreted as relatively low, and attributed to the success of the counselling protocol.43 In addition to catastrophic events, the literature also reports significant levels of personal stress and social dislocation, including the breakdown of family and social support networks.44 It is thought that individuals who ultimately choose to have predictive testing through an informed consent process may be a self-selected group and therefore less likely to suffer major negative consequences when compared with situations in which genotyping is performed unwittingly in persons or against their will.45
Common to both HD and vCJD is the fact that a positive test result would lead to individuals being informed they have a high likelihood of developing an invariably fatal disease, currently without treatment. Thus a positive result for vCJD may have similar implications to positive presymptomatic genotyping for HD.
POTENTIAL HARMS AND BENEFITS OF PRESYMPTOMATIC TESTING FOR VCJD
Using predictive genetic testing for HD as a paradigm for presymptomatic testing for vCJD, several harmful outcomes are possible, which could include: increased anxiety; depression; guilt; the burden of carrying such knowledge with constant vigilance for the onset of symptoms; discrimination in the workplace or when obtaining insurance; damage to self-esteem; and stigmatisation.
There are two key differences between HD and vCJD that may lead to an increased potential for harm when testing for vCJD. First, the number of people who would be eligible for vCJD testing would most likely be much greater than those eligible for testing for HD. The presentation of a large number of persons for testing may exceed available resources, militating against adequate individual counselling. This scenario could result in higher levels of catastrophic events compared with the rates reported in predictive testing for HD. Secondly, HD is not infectious whereas vCJD is. Consequently, presymptomatic genetic testing for HD will be of no direct benefit to society, while determining whether or not a person carries vCJD could potentially be of considerable public health benefit in the health care setting. There is therefore the possibility of coercion to undertake testing exerted by external authorities such as government agencies, with consequent infringement of personal autonomy. Restricted access to invasive medical procedures is yet another potential harm given the transmissibility of vCJD.
The clearest support for presymptomatic testing for vCJD is a possible benefit to public health. Testing would allow the exclusion of blood and tissue/organ donations from asymptomatic carriers. Preoperative and preprocedure screening could be systematically undertaken as part of infection control measures for patients undergoing a range of surgical and other invasive procedures involving higher risk tissues. Personal benefits from presymptomatic testing are also likely. A presymptomatic test for vCJD could be used to reassure the "worried well". Additional benefits include the opportunity for psychological adjustment, the opportunity for making realistic future plans (including end of life decisions, decisions about financial planning, and decisions about the timing of having children), and a reduced time between symptom onset and diagnosis.