Transmissible Spongiform Encephalopathies

Transmissible spongiform encephalopathies (TSEs) or commonly known as prion diseases are rare disease that is rapidly progressive and lethal. This disease is caused by transmissible agents of TSEs called prions (Kintosh & Collinge, 2003). Basically, prions induce abnormally folded proteins by converting the specific normal proteins that are found abundantly in the brain tissues in the prion form of proteins (Sasaki et al., 2005). These prion proteins lead to brain damage and the characteristic signs and symptoms of the prion diseases. They can be notable by lengthy incubation phases, spongiform changes related to neuronal loss, and a failure to induce an inflammatory response (Sundstrom & Dreher, 2003). Prion diseases mostly affect mammals including human and animals.

Fatal Familial Insomnia (FFI) is one of the prion diseases which affect human. It is an autosomal dominant inherited disease which caused by a mutation in the PRNP gene. As FFI is is known to be genetically inherited disorder which involve dominant mutated gene, it would be transmitted if one parent is a carrier or has the gene (Sundstrom & Dreher, 2003). This means their offspring has the probability of 50% for having the disease. The average age in which people suffer from the disease is 50 (Schenkein & Montagna, 2006). So, it is difficult to prevent the transmission of the disease to the childrens since the parents might not know they are having the disease. However, FFI is still considered as rare among human population because it would be lethal if an individual carries homozygous dominant alleles of the mutated gene and eventually can not be pass to the offspring.

A 'prion' hyphothesis states that the abnormally folded PrPSc forms of the prion protein may arise either spontaneously, or in patients carrying a mutation that makes misfolding more likely, or from an exogenous infective source. Once a misfolded form has arisen, other PrPc molecules are converted, propagating the disease in a form of a chain reaction (Kintosh & Collinge, 2003). Figure 1 shows the mechanism for prion conversion and propagation. Normal PrP (PrPc) interacts with an abnormal version of itself (PrPSc), which has the capability to transform the normal protein into the misfolded form and thus propagating the misfolded conformational information.

Figure 1: The molecular events that cause normal proteins to adopt an abnormally folded state

FFI disease is associated with the mutated gene of PRNP which provides information for the synthesis of prion protein PrPSc. A mutation can be found at codon 178 of the prion protein gene where there is a presence of asparagine (N) instead of the normal codon which is aspartic acid (D). Besides, FFI is also related to the presence of methionine codon at position 129 of the mutant alleles (Outeiro & Tetzlaff, 2007). When a prion protein enter