Next-generation sequencing enabled us to create a population-based expanded carrier screening (ECS) test that simultaneously tests for 50 serious autosomal recessive diseases. Before offering this test universally, we wanted to know what factors are related to intended participation and how the general public can be informed about the test without being influenced in their intention to participate. We studied this by measuring to what extent 'message framing' and 'narrative information' can influence people's intended participation. Data were collected by means of an online survey of 504 potential users, and the factors examined were based on the Theory of Planned Behaviour and on previous research on intended participation in preconception carrier screening. Message framing was manipulated by explaining the risk of couple carriership in different ways, while narrative information was provided to only half of the respondents. The factors most positively related to intended participation were perceiving benefits of the screening, having a positive attitude towards the screening, having no religion, having an actual child wish and experiencing the choice to participate as easy. Perceived benefits and a positive attitude were most influential factors by far. Message framing and narrative information had no significant effect on intended participation, reinforcing that message framing and narrative information can help to inform the general public about ECS without influencing their intended participation. Future research should study if the importance of perceived benefits and a positive attitude can be replicated when other factors are included and when actual participation is measured instead of intended participation. European Journal of Human Genetics (2017) 25, 793-800; doi:10.1038/ejhg.2017.74; published online 3 May 2017 INTRODUCTION Approximately 1-2 in 100 couples are at risk of having a child affected with a recessive genetic condition. 1 Population based expanded carrier screening (ECS) makes it possible to test couples before pregnancy for relevant recessive genetic conditions simultaneously. The preconception period might be considered a better time than the prenatal period, because it results in more reproductive options being available and termination of pregnancy can be avoided. 2 Next-generation sequencing techniques enabled us to create such a population-based ECS test that simultaneously tests for 50 serious autosomal recessive diseases. 3 The composition of this panel was based on previous research, multidisciplinary discussions and stakeholder meetings. Screening results are couple-based, so only couples who are both carriers of the same disease get positive results. However, before this test can be offered in a public healthcare setting, we needed a better understanding of the factors driving intended participation and how the general public could be better informed-but not influenced -in their intention to participate. This information is important because it is clear from previous research a...