There is an international effort of specialists contributing to a registry where we collect – theoretically in a homogeneous manner – data from patients with a rare disease and subforms thereof. My task is to look at it from the angle of age. Amongst many approaches, I also aim to investigate survival. Obviously, severe disease is associated with worse outcome; this is mostly self-explanatory and the argument appears circular. But what about age? Imaginably, survival is higher in the youngest group, and as people get older, survival is decreased. But this is true irrespective of having or not having a disease. Of course, there is no control group as a part of this registry (I speak about roughly 3000 individuals for the assessment of overall survival). So what am I really interested in? I would like to assess excess mortality caused by the disease, in different age groups.