A key concern in game-based learning is the level of authenticity that the game requires in order to have an accurate match of what the learners can expect in the real world with what they need to learn. In this paper, we show how four challenges to the designer of authentic games have been addressed in a game for an undergraduate course in a medical school. We focus in particular on the system of interaction with different characters of the game, namely, the patients and a number of professionals. Students use their personal phone and email application, as well as various web sites. First, we analyze the authenticity of the game through four attributes, authenticity of the character, of the content of the feedback, of the mode and channel of communication and of the constraints. Second, the perceived authenticity (by students) is analyzed. The later is threefold and defined by an external authenticity (perceived likeness with a real life reference), an internal authenticity (perceived internal coherence of the proposed situations) and a didactical authenticity (perceived relevance with respect to learning goals).