26 August 2005
The BMA published a report earlier this week on population screening and genetic testing. It reviews a number of well known issues: the impact of test results on insurance and employment, pharmacogenetics, pre-implantation genetic diagnosis and the benefits and pitfalls of screening programmes. Unfortunately, it provides little by way of new information or original recommendations.
A matter of much greater concern is its failure to encapsulate accurately the distinction between genetic screening and genetic testing. The first section of the report describes the essential characteristics of a screening programme and accurately sets out the differences between systematic and opportunistic screening. It makes clear that screening is a public health service in which members of a defined population are offered a test. It also encapsulates recent thinking about the nature of informed choice in screening, and how patients who are offered a screening test are encouraged to make a decision about whether or not they wish to participate.
The report then proceeds to characterise the distinction between genetic screening and genetic testing. It does so idiosyncratically, in a manner inconsistent with its own description of a screening programme. It suggests that the term screening should be used for testing members of a population for a disorder for which there is no prior evidence of the condition, although they may be part of a higher risk group, such as Ashkenazi Jews who are at risk of developing Tay Sachs disease, and reserves the term testing for those who know they are at risk, such as people belonging to families that may carry high penetrance genes associated with breast cancer or with a history of Huntington's disease. It is unclear why those who know they are at risk are seen by the authors to be conceptually different to those for which there is no prior evidence of the condition, although they may be part of a higher risk group. We suggest that the distinction that they try to make is unsound and has little relevance to the key difference between screening programmes and clinical tests, which is whether or not the test is explicitly offered to individuals as a public health service, as distinct from being used in the clinical setting when advice is sought by a patient.
It is our view that the term genetic screening should be used only when tests are offered (whether systematically or opportunistically) as part of a public health service, and genetic testing in all other circumstances. Our preference is that the testing of asymptomatic relatives of patients with inherited disorders should be referred to as cascade testing, although we concede that it would not be entirely inappropriate to call it cascade screening. We suggest that to use the word screening to refer generally to the testing of members of a population for a disorder for which there is no prior evidence of the condition (even if they may be part of a higher risk group) should be strongly avoided.
We regret that nowhere in the report is there any discussion about the definition or meaning of the term, a genetic test, since the term is capable of two entirely different meanings. The first meaning applies the word genetic to the disorder and confines itself to testing for genetic, that is inherited or heritable, disorders. In this sense any test for inherited disorders are genetic tests irrespective of the nature of the technology used. An ultrasound scan for adult polycystic disease of the kidney would be deemed a genetic test. The second meaning has the adjective genetic refer not to the disorder but to the technology used for the tests, thus equating genetic tests to tests based on DNA or chromosomes. Under this meaning, the use of a DNA based diagnostic to determine the increased risk of venous thromboembolism would be classified as a genetic test but not the use of an ultrasound scan for polycystic disease We believe that it is essential in any statement about genetic tests to make clear in which of these two senses it is being used.
A concentration by the report on the pitfalls of genetic screening is much to be regretted, since many of the ethical and social consequences that the report seeks to address are as much an issue for genetic testing as for genetic screening. The policy issues that arise when testing for inherited conditions are indeed different from those when testing for common complex disorders, but these differences are not those that distinguish screening from testing.