The presence of valine at codon 129 (129V) coupled with the same D178N mutation is associated with a very different phenotype reminiscent of CJD. FFI is linked to the presence of a D (aspartic acid) to N (asparagine) variation at codon 178 (D178N) coupled with the methionine at codon 129 (129M) on the mutant allele of the prion protein gene ( PRNP). sFI shares a very similar phenotype to FFI, but is not associated with a mutation in the prion protein gene.
Genetic or familial cases are linked to a mutation on the prion protein gene, and include several subtypes of Gerstmann Sträussler Scheinker syndrome, familial CJD, and fatal familial insomnia (FFI). Acquired cases include iatrogenic CJD, acquired by medical or surgical procedures, and variant CJD, usually acquired from consuming beef products contaminated with the agent of bovine spongiform encephalopathy. Sporadic cases, with no known environmental source of infection, include sporadic Creutzfeldt - Jakob disease (CJD), the most common human prion disease, and sporadic fatal insomnia (sFI), one of the least common. They are classified into three main groups: sporadic, acquired, and genetic. Human prion diseases are rare, transmissible, invariably fatal neurodegenerative diseases that are characterized by the accumulation of a misfolded host protein, the prion protein, in brain tissue. In patients with suspected prion disease, a characteristic change in sleep pattern can be an important clinical clue for identifying sFI or FFI polysomnography (PSG), genetic analysis, and nuclear imaging may aid in diagnosis.
Genetic tests identified no prion protein (PrP) gene mutation, but neuropathological examination and molecular study showed protease-resistant PrP (PrP res) in several brain regions and severe atrophy of the anterior-ventral and medial-dorsal thalamic nuclei similar to that described in FFI. Following death of this patient, an interview with a close family member indicated the patient's illness included a major change in her sleep pattern, corroborating the reported autopsy diagnosis of sFI. We report a case of a 33-year-old female who died of a prion disease for whom the diagnosis of sFI or FFI was not considered clinically. Sporadic fatal insomnia (sFI) and fatal familial insomnia (FFI) are rare human prion diseases.
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