For decades, it has been assumed that hereditary prion diseases follow Mendel's basic rules: a 50% chance of passing on the mutation to each child. But what if this pillar of classical genetics were wrong? This study reveals a surprising finding: the prion variants p.D178N and p.E200K are transmitted much more than 50%, reaching rates of 67%–71%, and even 78% when the father is a carrier of p.E200K. This is the first systematic evidence of distortion of the transmission ratio in genetic prion diseases, a phenomenon that completely alters our understanding of their inheritance.

Beyond the numbers, the study opens up a fascinating debate: why do these mutations ‘travel’ with an advantage during reproduction? Do mechanisms of embryonic selection, competition between gametes, or unknown functions of the prion protein play a role?

An article that redefines genetic risk and forces us to rethink how we advise affected families.