Non-therapeutic genetic testing in childhood presents a “myriad of ethical questions”; questions which are discussed and resolved in professional policy and position statements. In this paper we consider an underdiscussed but strongly influential feature of policy-making, the role of selective case and exemplar in the production of general recommendations. Our analysis, in the tradition of rhetoric and argumentation, examines the predominate use of three particular disease exemplar (Huntington’s disease, Tay-Sachs disease and sickle cell disease) to argue for or against particular genetic tests (predictive testing and testing for carrier status). We discuss the influence these choices have on the type and strength of subsequent recommendations. We argue that there are lessons to be drawn about how genetic diseases are conceptualised and we caution against the geneticisation of medical policy making.