Creutzfeldt-Jakob+disease


 * Creutzfeldt-Jakob Disease – A Genetic Cause with a Neurodegenerative Effect (By: Shivam Kapadia)**

Creutzfeldt-Jakob disease (CJD) is a human prion disease which results in the agglutination of specific prion proteins (PrP) bodies throughout the brain (Prusiner, 1998). This protein agglutination is the result of specific mutations in the normal PrP (PrPC) which cause conformational changes that form octamer subunits and induce indefinite polymerization. (Prusiner, 1998; Hesketh, Thompsett & Brown, 2012). This modified prion protein (PrPSC) is resistant to thermal, acidic and chemical agents, and even protease degradation; which makes CJD an incurable and untreatable disease (Prusiner, 1998). The novelty properties of PrPSC has challenged genetic and biological models, fuelling research to better understand the underlying genetic and biological mechanisms of PrPSC infectivity. This research is currently aimed at developing pre-emptive treatment to provide palliative care in already-diseased individuals.

toc =**1. Classification:**=

CJD is divided into three subtypes: familial, infectious(variant), and sporadic forms. Each subtype represents a specific mode of PrPSC infection, and transmission.

**1.1 Sporadic CJD (sCJD):**
The development of sporadic CJD is considered to be the human analogous to bovine spongioform encephalopathy (BSE) in cattle (Wells et al., 1987; Fornai et al., 2006). It is considered the prototypical human prion disease, sharing many neurological and histological features with familial CJD and variant CJD (Zeidler et al., 1997a, b). Genetically, sCJD is associated with the methionine-129 (M129) polymorphism which develops the most severe of symptoms (Capellari, Strammiello, Saverioni, Kretzchmar & Parchi, 2011). The disease also has some characteristic diagnostic features. These markers include: the presence of periodic sharp-wave complexes (PSWCs) on an electroencephalogram (EEG) measurement and a persistent elevation in the 14-3-3 protein, found in the cerebrospinal fluid (CSF) (Pocchiari et al., 2004). The presence of PWSCs and elevated 14-3-3 protein are thought to affect the age of onset of CJD and the duration of disease (i.e. survival time) (Pocchiari et al., 2004). Pocchiari etl al., (2004) have further suggested that a later onset of sCJD is correlated with a shortened survival time. This idea has been further probed by the Abiola group (2002) which has determined the presence of sex-specific factors that influence the age of disease onset, showing that females develop CJD later than do males.

**1.2 Familial CJD (fCJD):**
Familial CJD is a form of vertically transmitted prion disease where patients with fCJD have inherited one of many genetic markers and mutations which are associated with the onset of disease (Masters, Gajdusek & Gibbs, 1981). Many of these markers follow an autosomal-dominant inheritance pattern in diseased families (Owen et al., 1989; Collinge & Palmer, 1992). Some of these mutations include the E200K—D178N haplotype that associated with the onset of fCJD (Telling et al., 1996; Prusiner, 1998; Mead, 2006; Friedman-Levi et al., 2011). Other variants of the PRNP gene, include those containing insertions, as potential mutant genes involved in fCJD transmission (Owen et al., 1989). Familial CJD has also been implicated in patients carrying the M129 polymorphism, a feature that is also common to the sporadic form of Creutzfeldt-Jakob disease. Beyond the genetic underpinnings of this disease, fCJD shares many of the same clinical and morphological features associated with sporadic CJD (Prusiner, 1983).

**1.3 Variant CJD (vCJD):**
Variant CJD, also referred to as genetic or infectious CJD is form of iatrongenically transmitted PrPSC. CJD has been known to be the result of across-species barrier transmission of bovine spongioform encephalopathy (Wells et al., 1987; Prusiner, 1998). Accounts of iatrogenic transmission have also been documented. Cases of vCJD have been described in human pituitary growth hormone patients (Fradkin et al., 1991; Lewis et al., 2006). These patients received growth hormone therapy from cadaveric sources, which lead to the later onset of vCJD. Another common form of transmission has been through dura mater exposure during neurosurgery, or through contaminated neurosurgical equipment (Otto, 1987). Apart from epidemiological data, genetic research suggests that homozygous valine 129 polymorphic individuals are at a greater risk of contracting vCJD upon exposure relative to other individuals (Collinge, Palmer & Dryden, 1991). There is also emerging research from the last decade, suggesting that vCJD is clinically distinct from the prototypical sCJD. It has been shown that vCJD patients develop an earlier onset of the disease, corresponding earlier presence of psychiatric symptoms as compared to sCJD patients(Will et al., 1996). Such patients also lack the characteristic PSWCs shown through electroencephalography (Will et al., 1996). It has also been shown that structurally PrPSC differs post-translationally such that sCJD consists of monoglycosylated PrPSC while vCJD is diglycosylated in general (Collinge, Sidle, Meads, Ironside, & Hill, 1996).

=**2. Symptoms:**=

**2.1 Degenerative Symptoms:**
CJD is characteristically marked by global degeneration of the central nervous system. This is by means of spongioform degeneration, a form of vacuolation, where vacuoles formed are lined by the PrPSC. This degeneration can be presented in patterns, including striped formation and plaque inclusions.

**2.1.1 Clinical Phenotypes: **
Patients with CJD commonly present themselves with a wide media type="youtube" key="w9SJRdzpDBk" height="219" width="392" align="right"spectrum of conditions and symptoms. It has been suggested that as the PrPSC spreads throughout the brain, symptoms become increasingly severe and disabling. They often begin with personality changes, confusion, and tendency to forget things, which may or may not develop into some form of fully-developed personality disorder (Collinge et al., 1992). With the spread of the prion disease, patients may develop depression, apathy, experience unwarranted withdrawal, insomnia, and even unspecified anorexia (Zeidler et al., 1997a). One of the core features of CJD is the development of dementia, transitioning from milder forms to expressing extreme phenotypes, mimicking Alzheimer’s disease leading to global cognitive impairment, over a very short period of time (Kretzchmar, James, DeArmond, & Tateishi, 1996). Other neuropsychiatric changes involve myoclonus—motor jerks—ataxia, visual/cerebellar changes (Kretzchmar et al., 1996). Pyramidal and extrapyramidal symptoms a have also been associated with the progression of prion disease (Kretzchmar, 1996). It appears that clinical symptoms presented in CJD patients occur along spectrums of severity. With the progression of CJD, psychiatric conditions become worse, somatosensory activity is abolished leading to uncontrolled motions, muteness and paralysis (Zeidler et al., 1997b). (Below are videos of CJD cases - displaying clinical characteristics of prion disease) media type="youtube" key="videoseries?index=2" height="282" width="509" align="center"


 * 2.1.2 Neuropathological Phenotypes:**

It has been reported that the basal ganglia is especially prone to prion pathology, where the caudate nucleus is most commonly affected, spreading outwards to neighbouring regions such as the putamen (Ukisu et al., 2006). Prion infection has also been observed in the striatum, and several specific regions of the thalamus. (Tschampa et al., 2003). Magnetic resonance imaging (MRI) studies have shown that PrPSC preferentially targets certain nuclei and medial and posterior regions in the thalamus (Tschampa et al., 2003). This specificity of CJD infection of general areas of the brain may have to do with the physical ability of PrPSC to spread. Talbott, Plato, Sattenberg, Parker & Heindreich (2011) have suggested that the spread of PrPSC in CJD is limited to only certain regions of the brain because of a diffusion constraint, such that PrPSC is only able to diffuse out so far among neighbouring regions of the brain. Therefore, it appears that CJD may not be a result of global plaque formation, but rather more concentrated infectivity. CJD patients with the T183A—M129 haplotype are an example of where PrPSC spreading is specifically linked to severe fronto-temporal lesions and corresponding deficits, while mesencephalic regions and lower are generally preserved (Nitrini et al., 1997) This is further supported by work by Grasbon-Frodl et al. (2004) suggesting that lower than mesencephalic regions are less affected than higher cortical regions, in the case-study of a 40-year old man with a T183A mutation-causing sCJD. It has also been shown that sCJD patients show spongioform degeneration along cortical regions neighbouring the midline of the brain (Tschampa et al., 2007). This claims further support for the idea that the entire central nervous system (CNS) is not affected by CJD and that regions such as the basal ganglia, thalamus, and cortical areas such as the cingulate and insula around the midline may be affected, see **Figure 1**. (Ukisu, 2006; Tschampa, 2003, 2007).

**2.1.3 Histological Features:**
All forms of CJD are characterized by the presence of spongioform degeneration (i.e. vacuolation **Figures 2, 3**) and astrogliosis (Prusiner, 1998; Fornai et al., 2006). This vacuolation can be found throughout the brain; however, generally affects higher cortical regions. Regions such as the neocortex, thalamic region, basal ganglia and cerebellum have been commonly found as the sites of degeneration in the brain (Kretzchmar et al., 1996; Jarius et al., 2003; Mead, 2006). Microscopy studies on the cerebellum, for example, show linear plaque-like formations in its molecular layer (Jarius et al., 2003; Vital et al., 1998). There has also been increasing evidence of the presence of PrPSC in amyloidogenic plaques, suggesting a possible link between Alzheimer’s disease and CJD.

**2.2 Age-Related Symptoms:**
There has been increasing evidence over the last two decades, to suggest that there exists a special relationship between age of the patient and time of disease onset and even severity of the prion disease. Epidemiologic studies have shown that the later the development of prion disease is in an individual, the faster the disease spreads; implicating a shorter survival time for older patients (Weintjens, 1997; Pocchiari, 2004). An experiment conducted by Manolakou et al. (2001) using a mouse model has demonstrated that the incubation period of bovine spongioform encephalopathy (BSE) increased in progeny of younger maternal mice. These results appear to indicate that age-related effects may actually be transmitted across generations.

There is variable evidence suggesting sex-specific factors affecting aging. While it has been suggested that females tend to have longer incubation periods, it may be argued that this is only the case because epidemiologically females tend to outlive males (Abiola et al., 2002; Pocchiari et al., 2004). However, there is also evidence to counter this claim, stating that females actually develop the disease faster (Bruce & Dickinson, 1985).

Some of the longest known duration of symptoms to date involves a man diagnosed with familial CJD, whose symptoms progressed over the course of 13 years (Brown et al., 1984). Studying the genetic landscape of such individuals may offer invaluable insight towards palliative treatment and understanding disease resistance in humans. The effects of age have now further been implicated in affecting incubation time and the severity of symptoms together. A major study by Avrahami & Gabizon (2009) has shown that older mice are associated with a later disease onset, implicating longer periods of dormant incubation in the host. It has been further shown that older prion-diseased mice display milder symptoms than younger mice infected with prions. It appears that some of the characteristic feature of CJD including: astrogliosis, vacuolation and PrPSC agglutination, are less extensive in older aged group of mice. This finding has significant implications, suggesting that older infected individuals may have down-played symptoms which may allow them to have a less severe decline upon disease onset. This would support the idea of long-lasting diseased patients as described by Brown et al. (1984). However this evidence directs new questions in prion-related aging research. The relationship between later disease onset—shorter survival time and later disease onset—milder symptoms, requires greater scrutiny.

=**3. Genetic Mechanisms:**=

The aberrant PrPSC, responsible for causing CJD, is a mutated version of PrPC which contains a high number of beta-sheets that act as a template-mould to induce a conformational change in the normal PrPC converting into the mutant PrPSC (Prusiner, 1983, 1998; Oesch et al., 1985; Pan et al., 1993). This idea is called “Prusiner’s Theory” which describes that PrPSC does not replicate, but acts as a mould to induce a structural change in PrPC (Prusiner, 1998). During this process the PrPC undergoes permanent 20 structural changes converting its alpha-helices into beta-sheets (Pan et al., 1993). The conversion of the normal prion protein into PrPSC allows for homologous aggregation of the two proteins, which then upon interaction with another PrPC, repeat the same process, demonstrating that PrP aggregation is a self-propagating event (Ma & Lindquist, 2002a). This suggests that it is not necessarily the mutation in the PRNP gene that is responsible for prion pathogenicity, rather it is the modified proteomic structure that is pathogenic. This is so because both mutated and normal primary sequences of PrP can become aberrant. It is and idea supported by a hypothesis set forth by Ma, Wollmann & Lindquist (2002b) that PrPSC is not essential to neurotoxicity, that PrPC can also be toxic. This hypothesis explains that abnormal PrP agglutination is actually the cause of the disease and can occur via either form of the PrP protein. It is likely that the abnormal aggregating process that occurs is a result of PrPC that escapes interacting with the endosome-ubiquitinin-proteasome system (See **Figure 4.**) (Arnold et al., 1995).

**3.1 Mutations in the PRN****P Gene:**
Early experiments into determining the genetic basis of prion disease involved studying scrapie prions in the brain. It was found that there was a gene that encoded for a protein analogous to the prions found in the brain; and that prions were not self-replicatory carrying no DNA to replicate themselves (Oesch et al., 1985). This gene is now called the PRNP gene. There are a multiplicity of mutations, and changes in the genetic code that have been implicated different aspects of the prion disease process of CJD (Capellari et al., 2011). **Figure 5** below illustrates the structure of the PrPC (Zahn et al., 2000). ======

**3.1.1 E200K:**
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The E200K is a commonly identifiable marker for both sporadic and familial cases of CJD (Telling et al., 1996; Goldgaber et al., 1989). It is the result of a deamination of the dinucleotide CpG (Seno et al., 2000). It has been estimated that there is approximately a 56% penetrance rate of carriers developing some form of CJD (Brown, 1992; Kretzchmar et al., 1996). Creutzfeldt-Jakob patients with this genetic marker have are clinically associated with rapid dementia with myoclonus, pyramidal/extrapyramidal symptoms and cerebellar features such as the development of streak-like formations instead of classical plaque formations (Jarius et al, 2003).

**3.1.2 Octapeptide Repeat Insertions (OPRIs):**
There exists a region within the PRNP gene that contains octapeptide repeat insertions/deletions (OPRI/D) (Skworc et al., 1999). It has been implicated that 3 or more ORPRIs are involved in CJD; which are commonly found in the N-terminal of the PRNP gene (Capellari et al., 2011; Mead, 2006). However, studies have shown that the number of repeats is correlated with the age (i.e. time) of onset (Mead, et al., 2007). Specifically large repeats of OPRIs have been correlated with an earlier disease onset; and it has also been suggested that these greater number of OPRIs follow a similar pathological phenotype as the codon-129 polymorphism (Mead, 2006; Mead et al., 2007). These insertions are linked to the specific codon-129 polymorphisms, where heterozygous M/V-129 polymorphism, correlates with a later disease onset and fewer OPRI while homozygous M129 with more OPRIs are suggested to have an earlier disease onset (Mead et al., 2007). More specifically than this, experiments have shown that 5-7 OPRIs in the PRNP gene are linked, potentially causally, to preclinical personality changes, which are soon followed by dementia and ataxia, classical to CJD (Cochrain et al., 1996; Jansen et al., 2011). OPRIs are generally associated with classical symptoms of CJD: cerebellar ataxia, pyramidal and extrapyramidal symptoms, myoclonus and chora (Mead, 2006). However, a greater number of repeats, 8-9, are thought to form plaques in the cerebellum (Mead, 2006; Vital et al., 1998). Specifically the work by Vital et al. (1998) has shown that 4-7 OPRIs result in the classic string-like deposits in the molecular layer of the cerebellum, while 8-9 repeats are shown to form actual full-formed plaques (See **Figure 6a**).

**3.1.3 D178N:**
D178N is a point mutation converting Aspartic acid to Asparagine. It is one of many mutations that can be found on the PRNP gene that is associated with the development of CJD (Telling et al., 1996). It is one of the most common mutations to be found in CJD patients and commonly found in association with the codon-129 polymorphism which have been correlated together in a causal link to fCJD (Telling et al., 1996). The D178N-E200K haplotype is also commonly correlated with fCJD patients (Goldfarb et al., 1992; Monari et al., 1994). One of the most important features of this mutation is that it has been shown to have 100% penetrance (Kovacs et al., 2005). This point mutation also displays certain unique phenotypes. Patients with the D178N mutation appear to show insomnia, malfucintioning autonomic nervous system (dysautonomia), and myoclonus with localized degeneration of the anteroventral and dorsomedial thalamic regions (**Figure 6b**) (Mead, 2006).

**3.1.4 Codon-129 Polymorphism:**
While the codon-129 polymorphism is not a mutation per say, it is one of the most common and distinguishing genetic markers on the PRNP gene for CJD (Collinge & Palmer, 1992; Palmer et al., 1991). It is considered to be a susceptibility marker for the development of any form of CJD (Palmer et al., 1991). For example, the homozygous Valine (VV129) polymorphism is thought to make the PrP(C) more susceptible to conformational change, and therefore has been thought to be a major marker for the onset of sporadic and/or iatrogenic CJD (Collinge et al., 1991). Meanwhile the homozygous methionine (MM129) polymorphism has been associated with earlier disease onset in individuals. Associations of codon-129 and various other mutations in the PRNP gene have been suggested as factors causing specific phenotypes of CJD (Capellari et al., 2011). Some of these associations include the D178N-129M associated with the onset of fCJD (Telling et al., 1996). Another prominent association is the T183A-129M haplotype that affects frontal, temporal and mesencephalic regions (Grasbon-Frodl et al., 2004; Nitrini et al., 1997). Please review the work by Capellari et al. (2011) outlining the clinical pathological phenotypes associated with various codon-129 containing haplotypes, in CJD individuals. **Figure 7** below previews this work.

3.2 Seeding Mechanism for PrP Aggregation:
The “seeding hypothesis” is currently the leading theory that proposes a mechanism for PrP aggregation in prion diseases such as CJD. While copper has been commonly associated with many of the normal functions of the normal PrP(C), another metal has also been implicated in PrP activity (Davies & Brown, 2008). New experiments such the one conducted by Hesketh, Thompsett, & Brown (2012) however are looking at the role of manganese interactions with PrP(C) and its part in prion disease progression. It has been demonstrated that manganese induces structural changes in PrP(C) upon interaction (Tesenkova, Iodanova, Toyoda & Brown, 2004). These occur through manganese-binding at the N-terminal of PrP(C) (Brown et al., 2000). The structural changes in the PrP(C) convert it into PrP(SC), making the protein: more pathogenic to the CNS, protease-resistant, and cytotoxic (Brown et al., 2000; Davies & Brown, 2009; Uppington & Brown, 2008). This infectious form of PrP(C) is able to self-polymerize, by modifying the secondary structures of other normal PrP(C) proteins—restructuring the peptide to hold more β-sheets, forming octameric “seeds” which act as the basic unit to induce full-scale polymerization of PrP(SC) into aggregates, as seen in **Figure 8** (Brazier et al., 2008; Hesketh et al., 2012). These seeds are therefore, a manganese-bound-PrP(SC) complex, which have been found in the brains of CJD patients (Hesketh et al., 2007; Thackray, Klein, Aguzzi, & Bujdoso, 2002; Wong et al., 2001). Extensive research by the group of Hesketh et al. (2012), has shown that these “manganese prion seeds” lose infectivity over time, as a result of slowly-developing-permanent conformational changes in octameric structure and excess aggregation. They postulate that prion diseases, such as CJD, require a continuously generating supply of new manganese prion seeds in order to move from an incubation to a full blown disease, or else subthreshold accumulation will appear subclinical (Hesketh et al., 2007, 2012; Thackray, Klein, & Bujdoso, 2003). Furthermore, while Copper has been primarily associated with normal PrP function, Hesketh et al. (2012) have suggested a mechanism to explain why manganese instead of copper is responsible for the disease development (Davies & Brown, 2008). They have postulated that because manganese exists at around 10% of the concentration of copper in the brain, the interactions with PrP(C) are much rarer, and therefore, corresponds to the rare event of PrP(SC) production. =**4. Palliative Treatment & Research**=

As of date there is no curative treatment for any form of CJD. However, there do exist certain palliative treatments available to alleviate the disease symptoms. Many of these treatments are catered specifically towards a certain symtoms. Seizures are treated by anti-epileptics, myclonus with clonazepam, patients with ataxia require the use of feeding tubes, and antipsychotics are used to deal with psychotic behaviours, are some of the symptom-specific treatments available (Mastrianni, 2010). Currently there is a mass of ongoing research into the genetic mechanism of CJD and prion diseases whose information is being used to develop treatments. Experiments have shown in models that knocking out the PRNP gene during the symptomatic phase of CJD stops further accumulation of plaques, by stopping further conversion of PrP(C) (Mallucci et al., 2003). Another option being looked into is to use manganese-chelators to block manganese-induced PrP(C) conversion to PrP(SC), thereby allowing a longer incubation period (Brazier et al., 2010).

=**5. References**=

 Abiola, O. O., Iyegbe, C., Lantos, P., Plomin, R., Anderton, B. H., & Whatley, S. A. (2002). Profound Sex-Specific Effects on Incubation Times for Transmission of Bovine Spongioform Encephalopathy to Mice. //Intervirology, 45//, 56-58.  Arnold, J. E., Tipler, C., Laszlo, L., Hope, J., Landon, M., & Mayer, R. J. (1995). The abnormal isoform of the prion protein accumulates in the late-endosome-like organelles in scrape-infected mouse brain. //J Pathol, 176//(4), 403-411. doi: 10.1002/path.1711760412  Avrahami, D., & Gabizon, R. (2011). Age-related alterations affect the susceptibility of mice to prion infection. //Neurobiology of Aging, 32//, 2006-2015.  Brazier, M. W., Davies, P., Player, E., Marken, F., Viles, J. H. & Brown, D. R. (2008). Manganese binding to the prion protein. //J Biol Chem,// //283//, 12831–12839.  Brazier, M. W., Volitakis, I., Kvasnicka, M., White, A. R., Underwood, J. R., Green, J. E., … Collins, S. J. (2010). Manganese chelation therapy extends survival in a mouse model of M1000 prion disease. //J Neurochem, 114//, 440-451.  Brown, D. R., Hafiz, F., Glasssmith, L. L., Wong, B. S., Jones, I.M., Clive, C., & Haswell, S. J. (2000). Consequences of manganese replacement of copper for prion protein function and proteinase resistance. //EMBO J, 19//, 1180–1186.  Brown, P. (1992). The phenotypic expression of different mutations in transmissible human spongioform encephalopathy. //Rev Neurol (Paris), 148//(5), 317-327.  Brown, P., Gibbs, C. J., Rodgers-Johnson, P., Asher, D. M., Sulima, M. P., Bacote, A., Goldfarb, L. G., & Gajdusek, D. C. (1994). Human spongiform encephalopathy: The National Institutes of Health series of 300 cases of experimentally transmitted disease. //Ann Neurol,// //35//, 513-529.  Brown, P., Rodgers-Johnson, P., Cathala, F., Gibbs, C. J., & Gajdusek, D. C. (1984). Creutzfeldt-Jakob Disease of Long Duration: Clinicopathological Characteristics, Transmissibility, and Differential Diagnosis. //Ann Neurol, 16//, 295-304.  Bruce, M. E., & Dickinson, A. G. (1985). Genetic control of amyloid plaque production and incubation period in scrapie-infected mice. //J Neuropathol J Exp Neurol, 44//(3), 285-294.  Capellari, S., Strammiello, R., Saverioni, D., Kretzchmar, H., & Parchi, P. (2011). Genetic Creutzfeldt-Jakob disease and fatal familial insomnia: insights into phenotypic variability and disease pathogenesis. //Acta Neuropathol, 121//, 21-37. doi: 10.1007/s00401-010-0760-4  Cochrain, E. J., Bennett, D. A., Cervenakova, L., Kenney, K., Bernard, B., Foster, N. L., ... Brown, P. (1996). Familial Creutzfeldt-Jakob disease with a five-repeat octapeptide insert mutation. //Neurol, 47//(3), 727-733.  Collinge, J., Brown, J., Hardy, J., Mullan, M., Rossor, M. N., Baker, H., … Lantos, L. (1992). Inherited Prion Disease with 144 Base Pair Gene Insertion: 2. Clinical and Pathological Features. //Brain, 115//(3), 687-710. doi: 10.1093/brain/115.3.687  Collinge, J., & Palmer, M. S. (1992). Prion diseases. //Current Opinion in Genetics and Development, 2//, 448-454.  Collinge, J., Palmer, M. S., & Dryden, A. J. (1991). Genetic predisposition to iatrogenic Creutzfeldt-Jakob disease. //Lancet, 337//, 1441-1442.  Collinge, J., Siddle, K. C. L., Meads, J., Ironside, J. W., & Hill A. F. (1996). Molecular analysis of prion strain variation and the aetiology of “new variant” CJD. //Nature, 383//, 685-690.  Davies, P. & Brown, D. R. (2008). The chemistry of copper binding to PrP: is there sufficient evidence to elucidate a role for copper in protein function? //Biochem J, 410//, 237–244.  Davies, P. & Brown, D. R. (2009). Manganese enhances prion protein survival in model soils and increases prion infectivity to cells. //PLoS ONE, 4//, e7518.  Deriziotis, P., & Tabrizi, S. J. (2008). Prions and the proteasome. //Biochimica et Biophysica Acta, 1782//, 713-782.  Fornai, F., Ferrucci, M., Gesi, M., Bandettini di Poggio, A., Giorgi, F. S., Biagioni, F., & Paparelli, A. (2006). A hypothesis on prion disorders: Are infectious, inherited, and sporadic causes so distinct? //Brain Research Bulletin, 69//, 95-100.  Fradkin, J. E., Schonberger, L. B., Mills, J. L., Gunn, W. J., Piper, J. M., Wysowski, D. K., … Brown, P. (1991). Creutzfeldt-Jakob Disease in Pituitary Growth Hormone Recipients in the United States. //JAMA, 265//, 880-884.  Friedman-Levi, Y., Meiner, Z., Canello, T., Frid, K., Kovacs, G. G., Budka, H., … Gabizon, R. (2011). Fatal Prion Disease in a Mouse Model of Genetic E200K Creutzfeldt-Jakob Disease. //PLoS Pathogens, 7//(11), 1-14.  Goldfarb, L. G., Brown, P., Goldgaber, D., Asher, D. M., Srass, N., Granpera, G., …Gajdusek, D. C. (1989). Patientswith Creutzfeld-Jakob Disease and Kuru lack the mutation in the PRNP gene found in Gerstmann-Straussler syndrome, but they show a different double mutation in the same gene. //Am J Hum Genet, 45//, A189.  Goldfarb, L. G., Petersen, R. B., Tabaton, M., Brown, P., LeBlanc, A. C., Montagna, P., ... et al. (1992). Fatal familial insomnia and familial Creutzfeldt-Jakob disease: disease phenotype determined by a DNA polymorphism. //Science, 258//, 806-808.  Goldgaber, D., Goldfarb, L. G., Brown, P., Asher, D. M., Brown, W. T., Lin, S., Kascsak, R. J…. et al. (1989). Mutations in Familial Creutzfeld-Jakob Disease and Gerstmann-Straussler-Scheinker’s Syndrome. //Exp Neurol, 106//(2), 204-206.  Grasbon-Frodl, E., Lorenz, H., Mann, U., Nitsch, R. M., Windl, O., & Kretzchmar, H. A. (2004). //Acta Neuropathologica, 108//, 476-484. doi: 10.1007/s00401-004-0913-4  Hesketh, S., Sassoon, J., Knight, R., Hopkins, J. and Brown, D. R. (2007). Elevated manganese levels in blood and central nervous system occur before onset of clinical signs in scrapie and bovine spongiform encephalopathy. //J Anim Sci, 85//, 1596–1609.  Hesketh, S., Thompsett, A. R., & Brown, D. R. (2012). Prion protein polymerisation triggered by manganese-generated prion protein seeds. //J Neurochem, 120//, 177-189. doi: 10.1111/j.1471-4159.2011.07540.x Jansen, C., Voet, W., Head, M. W., Parchi, P., Yull, H. Verrips, A., …Rozemuller, A. J. M. (2011). A novel seven-octapeptide repeat insertion in the prion protein gene (PRNP) in a Dutch pedigree with Gerstmann-Straussler-Scheinker disease phenotype: comparison with similar cases from the literature. //Acta Neuropathol, 121//, 59-68. doi: 10.1007/s00401-010-0656-3  Jarius, C. Kovacs, G. G., Belay, G., Hainfellner, J. A., Mitrova, E., & Budka, H. (2003). Distinctive cerebellar immunoreactivity for the prion protein in familial (E200K) Creutzfeldt-Jakob disease. //Acta Neuropathologica, 105//, 449-454. doi: 10.1007/s00401-002-0664-z  Kovács, G. G., Puopolo, M., Ladogana, A., Pocchiari, M., Budka, H., van Duijn, C., … Mitrova, E. (2005). Genetic prion disease: the EUROCJD experience. //Hum Genet, 118//, 166-174. doi: 10.1007/s00439-005-0020-1  Kretzchmar, H. A. James, W., DeArmond, S. J., Tateishi, J. (1996). Diagnostic Criteria for Sporadic Creutzfeldt-Jakob Disease. //Arch Neurol, 53//, 913-920.  Lewis, A. M., Yu, M., DeArmond, S. J., Dillon, W. P. Miller, B. L., & Geschwind, M. D. (2006). Human Growth Hormone-Related Iatrogenic Creutzfeldt-Jakob Disease With Abnormal Imaging. //Arch Neurol, 63//, 288-290.  Mallucci, G., Dickinson, A., Linehan, J., Klohn, P. C., Brandner, S. and Collinge, J. (2003). Depleting neuronal PrP in prion infection prevents disease and reverses spongiosis. //Science, 302//, 871–874.  Ma, J., & Lindquist, S. (2002a). Conversion of PrP into a Self-Perpetuating PrPSC-like Conformation in the Cytosol. //Science, 298//, 1785-1788. doi: 10.1126/science.1073619  Ma, J., Wollmann, R., & Lindquist, S. (2002b). Neurotoxicity and Neurodegeneration When PrP Accumulates in the Cytosol. //Science,// //298//, 1781-1785. doi: 10.1126/science.1073725  Manolakou, K., Beaton, J., McConnell, I., Farquar, C., Manson, J., Hastie, N. D., ... Jackson, J. (2001). Genetic and environmental factors modify bovine spongioform encephalopathy incubation period in mice. //Proc Natl Acad Sci, 98//(13), 7402-7407.  Masters, C. L., Gajdusek, D. C., & Gibbs Jr., C. J. (1981). The familial occurrence of Creutzfeldt-Jakob disease and Alzheimer’s disease. //Brain, 104//, 559-580.  Mastrianni, J. A. (2010). The genetics of prion diseases. //Genetics in Medicine, 12//(4), 187-195.  Mastrianni, J. A., & Ross, R. P. (2000). The Prion Diseases. //Seminars in Neurology, 20//(3), 337-352.  Mead, S. (2006). Prion Disease Genetics. //European Journal of Human Genetics, 14//, 273-281. doi: 10.1038/sj.ejhg.5201544.  Mead, S., Webb, T. E., Campbell, T. A., Beck, J., Linehan, J. M., Rutherfoord, S., ... Collinge, J. (2007). Inherited prion disease with 5-OPRI: phenotype modification by repeat length and codon 129. //Neurol, 69//(8), 730-738.  Monari, L., Chen, S. G., Brown, P., Parchi, P., Petersen, R. B., Mikol, J., … Gambetti, L. A. (1994). Fatal familial insomnia and familial Creutzfeldt-Jakob disease: Different prion proteins determined by a DNA polymorphism. //Proc Natl Acad Sci USA, 91//, 2839-2842.  Nitrini, R., Rosemberg, S., Passos-Bueno, M. R., da Silva, L. S., Iughetti, P.,, Papadopoulos, M., … LeBlanc, A. (1997). Familial spongioform encephalopathy associated with a novel prion protein gene mutation. //Ann Neurol, 2//(42), 138-146.  Oesch, B., Westaway, D., Walchli, M., McKinley, M. P., Kent, S. B., Aebersold, R., ... Weissmann, C. (1985). A cellular gene encodes scrapie PrP 27-30 protein. //Cell, 40//(4), 735-746.  Otto, D. (1987). Creutzfeldt-Jakob disease associated with cadaveric dura (response). J Neurosurg, 67, 149.  Owen, F., Lofthouse, R., Crow, T. J., Baker, H. F., Poulter, M., Collinge, J., … Prusiner, S. B. (1989). Insertion in prion protein gene in familial Creutzfeldt-Jakob disease. //Lancet, 333//, 51-52.  Owen, F., Poulter, M., Collinge, J., Leach, M., Shah, T., Lofthouse, R., … Rossor, M. N. (1991). Insertions in the Prion Protein Gene in Atypical Dementia. //Exp Neurol, 112//, 240-242.  Palmer, M. S., Dryden, A. J., Hughes, J. T., & Collinge, J. (1991). Homozygous prion protein genotype predisposes to sporadic Creutzfeldt-Jakob disease. //Nature, 352//, 340-342.  Pan, K. M., Baldwin, M., Nguyen, J., Gasset, M., Serban, A., Groth, D., … Prusiner, S. B. (1993). Conversion of α-helices into β-sheets feature in the formation of the scrapie prion proteins. //Proc Natl Acad Sci USA, 90//, 10962-10966.  Pocchiari, M., Puopolo, M., Croes, E. A., Budka, H., Gelpi, E., Collins, S., … Will, R. G. (2004). Predictors of survival in sporadic Creutzfeldt-Jakob disease and other human transmissible spongioform encephalopathies. //Brain, 127//, 2348-2359. doi: 10.1093/brain/awh249  Prusiner, S. B. (1998). Prions. //Proc Natl Acad Sci USA, 95//, 13363-13383.  Prusiner, S. B., McKinley, M. P., Bowman, K. A., Bolton, D. C., Bendheim, P. E., Groth, D. F., & Glenner, G. G. (1983). Scrapie prions aggregate to form amyloid-like birefringent rods. //Cell, 35//(2-1), 349-358.

Satpute-Krishnan, P., Langseth, S. X., & Serio, T. R. (2007). Hsp104-Dependent Remodeling of Prion Complexes Mediates Protein-Only Inheritance. //PLoS Biol, 5//(2), e24. doi:10.1371/journal.pbio.0050024

 Seno, H., Tashiro, H., Ishino, H., Inagaki, T., Nagasaki, M., & Morikawa, S. (2000). New haplotype of familial Creutzfeldt-Jakob disease with a codon 200 mutation and a codon 219 polymorphism of the prion protein gene in a Japanese family. //Acta Neuropathol, 99//(2), 125-130.  Skworc, K. H., Windl, O., Schulz-Schaeffer, W. J., Giese, A., Berqk, J., Nӓgele, A., … Kretzchmar, H. A. (1999). Familial Creutzfeldt-Jakob disease with a novel 120-bp insertion in the prion protein gene. //Ann Neurol, 46//(5), 693-700.  Talbott, S. D., Plato, B. M., Sattenberg, R. J., Parker, J., & Heidenreich, J. O. (2011). Cortical restricted diffusion as the predominant MRI finding in sporadic Creutzfeldt-Jakob disease. //Acta Radiologica, 52//, 336-339. doi: 10.1258/ar.2010.100355  Telling, G. C., Parchi, P., DeArmond, S. J. Cortelli, P., Montagna, P., Gabizon, R., … Prusiner, S. B. (1996). Evidence for the Conformation of the Pathologic Isoform of the Prion Protein Enciphering and Propagating Prion Diversity. //Science, 274//, 2079-2082.  Thackray, A. M., Klein, M. A., Aguzzi, A. & Bujdoso, R. (2002). Chronic subclinical prion disease induced by low-dose inoculum. //J Virol 76//, 2510–2517.  Thackray, A. M., Klein, M. A. & Bujdoso, R. (2003). Subclinical prion disease induced by oral inoculation. //J Virol, 77//, 7991–7998.  Tschampa, H. J., Kallenberg, K., Kretzchmar, H. A., Meissner, B., Knauth, M., Urbach, H., Zerr, I. (2007). Pattern of Cortical Changes in Sporadic Creutzfeldt-Jakob Disease. //Am J Neuroradiol, 28//, 1114-1118. doi: 10.3174/ajnr.A0496  Tschampa, H. J., Mürtz, P., Flacke, S., Paus, S., Schild, H. H., & Urbach, H. (2003). Thalamic Involvemet in Sporadic Creutzfeldt-Jakob Disease: A Diffusion-Weighted MR Imaging Study. //Am J Neuroradiol, 24//, 908-915.  Tsenkova, R. N., Iordanova, I. K., Toyoda, K. & Brown, D. R. (2004). Prion protein fate governed by metal binding. //Biochem Biophys Res Commun, 325//, 1005–1012.  Ukisu, R., Kushihashi, T., Tanaka, E., Baba, M., Usui, N., Fujisawa, H., & Takenaka, H. (2006). Imaging of Early Stage Creutzfeld-Jakob Disease: Typical and Atypical Manifestations. //Radiographics//, //26//, S191-S204.  Uppington, K. M. & Brown, D. R. (2008). Resistance of cell lines to prion toxicity aided by phospho-ERK expression. //J Neurochem, 105//, 842–852.  Vital, C., Gray, F., Vital, A., Parchi, P., Capellari, S. Petersen, R. B., … Gambetti, P. (1998). Prion encephalopathy with insertion of octapeptide repeats: the number of repeats determines the type of cerebellar deposits. //Neuropathol Appl Neurobiol,// //24//, 125-130.  Wells, G. A., Scott, A. C., Johnson, C. T., Gunning, R. F., Hancock, R. D., Jeffrey, M., ... Bradley, R. (1987). A novel progressive spongioform encephalopathy in cattle. //Vet Rec, 121//, 419-420.  Will, R. G., Ironside, J. W., Zeidler, M., Cousens, S. N., Estibeiro, K., Alperovitch, A., … Smith, P. G. (1996). A new variant of Creutzfeldt-Jakob disease in the U.K. //Lancet, 347//, 921-925.  Wientjens, D. P. W. M. (1997). Epidemiology of Creutzfeldt–Jakob disease: Incidence, risk factors and survival in European studies [dissertation]. Rotterdam: Erasmus University.  Wong, B. S., Chen, S. G., Colucci, M., Xie, Z., Pan, T., Liu, T., … Brown, D. R. (2001). Aberrant metal binding by prion protein in human prion disease. //J Neurochem, 78//, 1400-1408.  Zahn, R., Liu, A., Lührs, T., Riek, R., von Schroetter, C., Garcia, F. L., … Wüthrich, K. (2000). NMR solution structure of the human prion protein. //Proc Natl Acad Sci 97//(1), 145-150.  Zeidler, M., Johnstone, E. C., Bamber, R. W., Dickens, C. M., Fisher, C. J., Francis, A. F., … Will, R. G. (1997a). New variant Creutzfeldt disease: psychiatric feature. //Lancet, 350//, 908–10.  Zeidler, M., Stewart, G. E., Barraclough, C. R., Bateman, D. E, Bates, D., Burn, D. J., …, & Will, R. G. (1997b). New variant Creutzfeld-Jakob disease: neurological features and diagnostic tests. //Lancet,// //350//, 903-907.