neurologic disorders
Overview of Prion Diseases
Transmission of prion diseases
Prion diseases originate Sporadically (apparently starting spontaneously, without a known cause) Via genetic inheritance (familial) Via infectious transmission Sporadic prion diseasesare the most common, with a worldwide annual incidence of about 1 to 2/1 million people. How PrPScfirst forms is unknown. Familial prion diseasesare caused by defects in the PrP gene (PRNP), which is contained in the short arm of chromosome 20. The genetic mutations causing prion diseases are almost all autosomal dominant; ie, they cause disease when they are inherited from only one parent. Also, penetrance is variable; ie, depending on the type of mutation, a variable percentage of carriers of the mutation have clinical signs of the disease during their lifetime. More than 50 mutations exist. Different gene defects cause different types of prion disease, which include Creutzfeldt-Jakob Disease (CJD) (CJD) Gerstmann-Sträussler-Scheinker Disease (GSS) (GSS) Diseases with mixed features of CJD and GSS Diseases that are clinically and pathologically different from other prion diseases, such as prion disease associated with diarrhea and autonomic neuropathy Fatal Insomnia (FFI) To date, researchers have identified only one mutation that causes FFI, the familial form of fatal insomnia. . Small abnormalities in specific codons (nucleotide sequences that are the building blocks of genes), which on their own do not cause disease, may determine the predominant symptoms and rate of disease progression in familial and other prion diseases ( Transmission references ). Infectiously transmitted prion diseasesare rare. They can be transmitted From person to person: Iatrogenically, via organ and tissue transplants, use of contaminated neurosurgical instruments, or, rarely, blood transfusion (as in vCJD); or via cannibalism (as in kuru) From animal to person: Via ingestion of contaminated beef (as in vCJD) Prion diseases are not known to be contagious through casual person-to-person contact. Prion diseases occur in many mammals (eg, mink, elk, deer, domestic sheep and cattle) and can be transmitted between species via the food chain. However, transmission from animals to humans has been observed only in vCJD, after people consumed beef from cattle with bovine spongiform encephalopathy (BSE, or mad cow disease). In most US states, Canada, South Korea, Norway, Finland, and Sweden ( Transmission references ), there is concern that chronic wasting disease (CWD), the prion disease of elk and deer, may be transmissible to people who hunt, butcher, or eat the affected animals. Experimental evidence suggests that transmission of CWD from animals to humans may be possible, and recent data indicate that the barriers between species may be weakened when CWD has been transmitted from animal to animal several times (as may happen in the wild [ 