A number sign (#) is used with this entry because fatal familial insomnia (FFI) is associated with mutation in the prion protein gene (PRNP; 176640). Description Fatal familial insomnia is a prion disorder showing autosomal dominant inheritance. It is clinically characterized by insomnia with or without a diurnal dreaming state, hallucinations, delirium, and dysautonomia preceding motor and cognitive deterioration. FFI is specifically associated with the asp178-to-asn mutation of the PRNP gene (D178N; 176640.0010) when the amino acid at position 129 is methionine (M129V; 176640.0005). The D178N mutation and the val129 allele results in Creutzfeldt-Jacob disease (CJD; 123400) (see 176640.0007) (Goldfarb et al., 1992).

Fatal familial insomnia (FFI) is a very rare form of prion disease (see this term) characterized by subacute onset of insomnia showing as a reduced overall sleep time, autonomic dysfunction, and motor disturbances.

Fatal familial insomnia (FFI) affects the thalamus , the part of the brain that controls the sleep-wake cycle. Symptoms typically begin between the ages of 40-60 years. The most common symptoms are sleep disturbance, psychiatric problems, weight loss, and balance problems. Other symptoms include high blood pressure, excess sweating, and difficulty controlling body temperature. These symptoms tend to get worse over time. FFI is usually fatal in 6-36 months. Almost all cases of FFI occur due to a specific variant in the PRNP gene and are inherited in an autosomal dominant pattern.