Fatal familial insomnia around the world. Introduction.

Despite decades of research, much intensified in recent years, transmissible spongiform encephalopathies (TSEs) or prion diseases have remained enigmatic in many aspects. Among these, the intricate connection between infectivity and genetics, genotype-phenotype correlation, and pathogenesis of brain damage are major problems in need of clarification. Fatal familial insomnia (FFI) appears as an ideal model situation for answering some of these problems: it has been understood to have a distinctive clinicopathological phenotype based on a specific genotype as well as transmissibility. However, as always with good science, new data prompts more questions than it is able to answer. The following survey of FFI cases in Europe and around the world is no exception from this rule.