Over the last years, several private companies have developed direct-to-consumer (DTC) genetic testing services that directly propose to consumers genetic tests outside the context of a genetic counseling session (for review see Bloss et al1). The argument usually presented by these companies is that DTCs facilitate access to testing and increase consumer awareness of the risk of developing diseases. The number of available DTC tests is rapidly increasing with tests for Mendelian disorders resulting from a deleterious mutation to tests for multifactorial diseases, due to a combination of DNA variants. Most of the DTC tests analyze common DNA variants, which are present in the general population and have been shown by genome-wide association studies (GWAS) to be associated with a low or moderate increase of disease risk. Although there is no reason why private companies could not participate in genetic testing, as long as their practice respects the general guidelines in genetics, the development of such DTC genetic testing raises numerous issues. First, DTC is clearly taking advantage of the underestimation by the consumers of the complexity of the disease genetic determinism. It is urgent to clarify the fact that, while in monogenic disorders a deleterious mutation is the key determinant, the majority of frequent diseases involve a combination of numerous genetic variations, such as SNPs, each conferring a very slightly increased risk, usually in the magnitude of 1.2, as measured by the numerous GWAS studies published over the last years. Second, the realization of a genetic analysis requires a specific, personalized information delivered before the test in order to explain the medical benefits of the test, the limits of the test and the medical consequences of a positive result, in terms of follow-up, investigations and treatment, not only for the tested individual but also for his family. Finally, the estimation of the genetic risk for an individual to develop a specific disease must be based on the evaluation of the phenotype and of the family history. Therefore, there is no evidence that ‘positive’ CTD tests, based only on the screening for common genetic variations, will justify a specific medical follow-up and procure a medical benefit to individuals. Furthermore, positive tests may induce psychological distress, even if the individual risk remains low. In contrast, ‘negative’ results might inappropriately reassure the patient concerning his risk to develop a disease. These limits and risks of DTC services are illustrated by one of the first studies on this topic published in this issue of the Journal.2 This study has compared the performance of the personal genome screening (PGS) from Navigenics with the family history-based risk-assessment (FHRA) commonly used in genetic counseling sessions. A total of 44 participants were included in this study and their risks for breast, prostate and colorectal cancers were evaluated. FHRA classified 8, 2 and 7 patients as high-risk subjects for each cancer type, respectively, whereas 1, 2 and 0 subjects were classified as high-risk subject according to PGS. More importantly, PGS classified at high risk only 1 of the 9 subjects harboring a highly penetrant BRCA or colorectal cancer mutation.

After the revolution initiated by the next-generation sequencing, which has uncovered the extent of human DNA variability, revealed that diseases, initially considered as multifactorial, result in fact from de novo deleterious mutations and that disorders previously viewed monogenic may have an oligogenic inheritance, the challenge for medical geneticists is not anymore the detection but the interpretation of genetic variations. Our awareness of the complexity of the disease genetic determinism should lead more and more to a clinical guidance and a sophisticated interpretation. In this context, the development of DTCs appears as a paradox▪