Fatal Familial and Sporadic Insomnia

Fatal familial insomnia is a prion disease characterized by severe sleep impairment and dysautonomia associated with severe thalamic atrophy with minimal or no spongiform degeneration. Genetically, Ffiis linked to aspartic acid to asparagine variation at codon 178 of the prion protein gene (D178N) coupled to the methionine codon 129 (D178N-129M) the site of a common methionine/valine polymorphism. Age at onset is variable but is on average 50 years and the disease duration is between 7 and 84 months, with shorter duration in cases that are methionine homozygous at codon 129 (average 11 months) and longer in patients that are methionine/valine heterozygous (23 months) although there is considerable overlap. Positron emission tomography with fluorodeoxyglucose can diagnose the disease in the presymptomatic phase. The sporadic form of fatal familial insomnia, sporadic fatal insomnia, has very similar clinical and histopathological phenotypes to those associated with fatal familial insomnia. Genetically, all cases of sporadic fatal insomnia reported to date are homozygous methionine at codon 129 of the prion protein gene. Both fatal familial insomnia and sporadic fatal insomnia are associated with a protease-resistant prion protein with the electrophoretic mobility of the protease-resistant prion protein type 2. Currently there is no effective treatment for fatal familial insomnia and sporadic fatal insomnia. Modeling of fatal familial insomnia has been attempted using transgenic mice.