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Variant Creutzfeldt–Jakob Disease
V Variant Creutzfeldt–Jakob Disease S Notari, X Xiao, M Shimoji, J Yuan, H Bi, I Cali, Q Kong, and W-Q Zou, Case Western Reserve University School of Medicine, Cleveland, OH, USA ã 2010 Elsevier Ltd. All rights reserved.
Glossary Ataxia – Inability to coordinate voluntary movements, leading to unsteady movements and staggering gait; most often associated with lesions of the cerebellum. Bovine spongiform encephalopathy (BSE) – A prion disease of cattle; the bovine prions are transmitted to humans through consumption of contaminated meat products, and lead to variant Creutzfeldt–Jacob Disease (vCJD). Cellular prion protein (PrPC) – A normal glycoprotein attached to the cell surface through a glycosylphosphatidylinositol (GPI) anchor most abundant in the brain but also in other organs. Myoclonus – A sudden twitching of muscles or parts of muscles, without rhythm or pattern. Psychiatric symptoms – Early symptoms frequently seen in vCJD including depression, anxiety, and withdrawal. Scrapie prion protein (PrPSc) – An infectious and pathogenic protein also called prion that derives from PrPC via a structural transition from a-helix into b-sheet. In sharp contrast to PrPC, PrPSc is detergent-insoluble, resistant to protease, prone to aggregation, and infectious. Variant Creutzfeldt–Jakob disease (vCJD) – A variant form of Creutzfeldt–Jakob disease acquired from the consumption of BSE-contaminated meat. It is characterized by young age at onset; early dominant psychiatric symptoms followed by neurologic deficits (cerebellar ataxia, involuntary movements, dystonia, and myoclonus); abundant florid prion plaques; and PK-resistant PrPSc in the brain.
Definition and History Variant Creutzfeldt–Jakob disease (vCJD) belongs to a group of highly heterogeneous and fatal transmissible spongiform encephalopathies, or prion diseases, that affect both animals and humans. Animal prion diseases include scrapie in sheep and goats, bovine spongiform encephalopathy (BSE or mad cow disease) in cattle, as well as chronic wasting disease in deer and elk. In humans, prion diseases can be sporadic, inherited, or acquired by infection, depending on their etiology. They mainly manifest four major phenotypes: CJD, Gerstmann–Stra¨ussler–Scheinker disease, kuru, and fatal familial insomnia. As a group, prion diseases are characterized clinically by disorders of cognition and movement; pathologically by spongiform degeneration, neuronal loss, and astrocytosis; and biochemically by deposition of an infectious proteinaceous pathogen called prion or scrapie prion protein (PrPSc). In addition to these basic characteristics, vCJD also possesses a unique identity: early dominant psychiatric symptoms followed by late neurologic deficits, young age at death, presence in the brain of florid prion plaques, and an abnormal PrP that is resistant to protease digestion and displays distinctive electrophoretic characteristics (Figure 1). vCJD was first discovered by Will and colleagues in the United Kingdom in 1996. Its discovery, together with the immediate demonstration of the causal link between vCJD and BSE, represent milestones in the history of prion disease. Not only did these findings demonstrate, for the first time, that prion disease could be transmitted from animals to humans, but they also greatly accelerated the establishment of surveillance and control of prion diseases. Following the outbreak of BSE, the surveillance of CJD was heightened in the United Kingdom in 1990 in order to monitor any changes in this condition that might be associated with transmission of BSE to humans. Subsequently,
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(a)
(b)
kDa
Di.Mono.-
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Un.Type 1 Type 2 Type 2 (c)
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vCJD
Figure 1 PrPSc detection by immunohistochemistry and Western Blot analysis. Immunohistochemistry of brains affected by vCJD (a) and sCJD (b), and of a normal brain (c) with anti-PrP antibody 3F4. Amount and pattern of distribution of PrPSc are different between vCJD, where PrPSc forms clumps, and sCJD, which shows dot-like formations. No PrP is seen in the normal brain (J. Ironside, National CJD Surveillance Center, Edinburgh, UK, and P. Gambetti, National Prion Disease Pathology Surveillance Center, Cleveland, OH, USA). Probed with 3F4 (d) Homogenates of the frontal cortex from sCJDMM1 (type 1), sCJDMM2 (type 2) and vCJD were treated with proteinase K (PK) prior to Western blotting with 3F4 antibody. The PK-resistant PrP core fragments from sCJD exhibit a dominant middle band corresponding to monoglycosylated PrP and a lower band corresponding to unglycosylated PrP migrating at 21 kDa (PrPSc type 1) or at 19 kDa (PrPSc type 2). In contrast, the PK-resistant PrP core fragments from all vCJD show a single uniform profile: a dominant upper band corresponding to diglycosylated PrP and a lower band migrating at 19 kDa. Di.: diglycosylated PrP; Mono.: monoglycosylated PrP; and Un.: unglycosylated PrP.
in 1993, the European Union started a project involving the majority of European countries (extended to all member states in 1998) in which common methodologies and criteria for case definition were adopted. In 1995 and early 1996, through these efforts a number of cases of CJD were identified in the United Kingdom with a unique phenotype distinct from sporadic CJD. By March 1996, ten cases of CJD sharing a very similar phenotype had been collected: the patients were of a young age at death (mean 29 years vs. 66 years in sporadic CJD); and the illness was characterized by long duration (mean 14 months vs. 4.5 months in sporadic CJD) and an unusual and remarkably uniform clinical presentation, distinct from that previously seen in CJD. Subsequent animal inoculation studies confirmed that this novel human prion disease is caused by the same prion strain that causes BSE in cattle.
Pathogenesis vCJD, along with kuru of New Guinea, and iatrogenic CJD, are the three forms of the disease known to date to be acquired by infection. However, unlike kuru and iatrogenic CJD (caused, respectively, by human-to-human transmission through ritual cannibalism, or medical and surgical procedures), vCJD is caused by transmission from cattle,
most likely through an oral route by consumption of prioncontaminated meat products, or possibly through parenteral routes. In addition to the acquired form, the other forms of prion diseases comprise sporadic CJD, the most common form and genetically determined or familial CJD. However, regardless of their distinct etiologies, all prion diseases share a fundamental pathogenetic mechanism: the conversion of the normal or cellular PrP (PrPC) into an isoform, identified as scrapie PrP (PrPSc). PrPSc is the only known component of prion that is believed to be pathogenic and infectious but at the same time (and in contrast to viruses and bacteria) is thought to be free of nucleic acids. It is postulated that in acquired prion diseases, including vCJD, prions are acquired by exogenous infection whereas in sporadic and familial CJD prions form spontaneously, either as a result of a random misfolding event or as a result of the presence of PrP destabilizing mutation. Most of PrPC is full-length, diglycosylated, and attached to the cell surface via a glycosylphosphatidylinisotol (GPI) anchor; but small amounts of PrPC may be N-terminally truncated, monoglycosylated or unglycosylated, anchorless, or cytosolic. PrPC and PrPSc share their primary structure. The critical difference between these two proteins lies in the conformation, in that PrPC converts into PrPSc through an a-helix to b-sheet structural transition which results in profound differences in the physicochemical and biological
Variant Creutzfeldt–Jakob Disease
properties of the two conformers. PrPSc is rich in b-sheets and is detergent-insoluble, multimeric, resistant to proteinase K (PK) treatment, and infectious. In contrast, PrPC is rich in a-helix, detergent-soluble, monomeric, sensitive to PK, and noninfectious. Although there is no doubt that the coexistence of PrPSc and PrPC in the central nervous system (CNS) is a prerequisite for prion diseases, the role of these two PrP conformers in the pathogenesis of prion disease is not completely understood. Two major hypotheses have been proposed to explain how changes in PrPC conformation could cause neurodegeneration: first, functional gain, in which prion pathology is attributable to the acquisition of toxic function; and second, functional loss, in which a PrPC physiologic activity is lost upon conversion to or interaction with PrPSc. A Single Uniform Prion Strain Based on gel mobility and glycoform ratio, PrPSc detected in sCJD can be divided into two types: PrPSc type 1 with an unglycosylated PrP migrating at 21 kDa and a dominant N-terminal protease cleavage site at residue 82; and PrPSc type 2 with an unglycosylated PrP migrating at 19 kDa and a cleavage site at residue 97 on the gel (Figure 1). Moreover, all PrPSc species from sCJD exhibit a dominant monoglycosylated PrP. In contrast, PrPSc from all vCJD examined so far is invariably of a dominant diglycosylated PrP and a 19-kDa unglycosylated PrP with a primary cleavage site at residue 97 (Figure 1). The electrophoretic profile of PrPSc detected in all vCJD cases is virtually identical to that found in BSE, which indeed implies that prion present in vCJD derives from BSE. Polymorphism at Residue 129 of PrP It has been believed that polymorphism at residue 129 of PrP (either methionine (M) or valine (V)) is associated with susceptibility to human prion. Although most sporadic CJD occurs in individuals homozygous for 129 MM, it also affects individuals with genotype 129 MV or 129 VV. Remarkably, all clinically affected vCJD cases studied so far have been 129 MM homozygous. However, the identification, in an anonymous screening study, of two positive appendix tissues from subjects with 129 VV genotype, together with the description of an asymptomatic case of vCJD in an 129 MV patient infected by blood transfusion, highlight the possibility that polymorphisms rather than 129 MM could also be susceptible to variant CJD although they might exhibit atypical phenotypes such as a subclinical form. Involvement of the Lymphoreticular System The distinctive pathogenesis of vCJD in comparison with other forms of CJD is also reflected in the involvement of
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the lymphoreticular system. PrPSc is readily detectable in lymphoreticular tissues in vCJD including gut-associated lymphoid tissue, tonsil, spleen, appendix, and lymph nodes, whereas it is only detected in the spleen of some sporadic CJD using highly sensitive methods. Prion neuroinvasion bears remarkable similarities to neuroinvasion by viral agents. Oral or Parenteral Transmission Route Presumably, all clinically infected vCJD cases are contracted orally, through consumption of contaminated meat products derived from BSE cattle. But exactly how the BSE prion spreads from the gastrointestinal system to the CNS remains an unresolved question. It has been hypothesized that the invading prions undergo two phases to reach the CNS: they accumulate and replicate in the lymphoreticular organs (primary phase) and then disseminate to the CNS through the peripheral nerves. Studies in prion-infected animals revealed that the autonomous nervous system, including both vagal and sympathetic nerve fibers, contributes to the spread of orally administered prions. These results are consistent with a finding that PrPSc is detected in the sympathetic nervous system (stellate and celiac ganglia) in vCJD but not in sCJD. In addition to the oral route, recent identification of three cases of transfusion-associated vCJD prion infection has raised significant concerns that there may be substantial risks of iatrogenic transmission of vCJD prions. Surprisingly, an asymptomatic transfusionassociated vCJD case exhibited MV polymorphism at residue 129 but no neurologic disorders and no prion-related neuropathologic changes. Moreover, PrPSc was detectable only in the lymphoreticular tissues but not in the brain. It is unclear whether this preclinical stage resulted from the parenteral route transmission or from the 129 MV heterozygous polymorphism.
Epidemiology and Risk Factors Variant CJD has been reported in many countries particularly in Europe. As of February 2009, 214 cases of vCJD have been identified worldwide, mostly in the United Kingdom (Table 1). The patients in Ireland, Canada, and the United States of America had spent significant periods of time in the United Kingdom, which suggests that these patients contracted the disease through dietary exposure to BSE in the United Kingdom. However, the Italian patient and most French patients had not visited the United Kingdom. How were these patients infected by the BSE prion? Brandel and colleagues recently conducted a study in which they demonstrated that the British and French vCJD cases manifested very similar clinical, histopathologic, and molecular features and concluded that the two sets of vCJD patients shared the same
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prion strain. These findings highlight two issues. First, they raise the question of the origin of the infectious prion in the French vCJD: whether it originates from British BSE or from indigenous French BSE; and second, Table 1 disease
Number of vCJD reported and countries with the
Country
Number of cases
Unite Kingdom France Spain Republic of Ireland United States of America The Netherlands Portugal Saudi Arabia Italy Canada Japan Total
169 23 5 4 3 3 2 2 1 1 1 214
Data as of February 2009. Quoted from the European and Allied Countries Study Group of CJD (EUROCJD). Table 2
whether vCJD worldwide is caused by one prion strain or whether all vCJD cases carry the same British prion strain. It is critical that these two issues be clarified, so that the diffusion of the BSE epidemics through different continents can be understood and arrested.
Clinical Features, Diagnostic Work-Up and Tests, and Diagnostic Criteria It is widely believed that the high heterogeneity of sporadic CJD results mainly from the chameleon-like conformation of prions. Indeed, at least five clinical subtypes of sCJD have been identified based on a combination of PrPSc types and PrP polymorphism at residue 129. Surprisingly, the clinical manifestations of vCJD linked to a single uniform prion strain (PrPSc type 2 with the homozygous MM) remain relatively heterogeneous (Table 2). According to an analysis of clinical features of the first 100 cases by Will and colleagues, 63% of cases present with psychiatric symptoms alone, 15% with isolated neurologic symptoms and 22% with mixed features. Patients with vCJD usually
Differences between variant and sporadic CJD Variant CJD
Typical sporadic CJD (MM1)
29 years 14 months Presentation: affective or psychotic disorder, persistent pain, sensory symptoms, sometimes gait ataxia or dysarthria Later stage: ataxia, dementia
65 years 4 months Presentation: cognitive impairment, ataxia, mental, and visual signs
Pulvinar 90% ‘Typical’ 0% Positive
Caudate/putamen 60% ‘Typical’ 80% Negative
Multiple florid plaques in H&E sections, numerous small clusters of plaques in PrP stained sections, amorphous pericellular and perivascular PrP accumulation Severe spongiform change, perineuronal and axonal PrP accumulation Marked astrocytosis and neuronal loss
Reticular and perineuronal PrP accumulation in gray matter
Widespread fine spongiform degeneration, astrogliosis, neuronal loss; punctate PrP immunoreactivity; ‘brush stroke’ pattern in cerebellar molecular layer Fine spongiform degeneration and astrogliosis; punctate PrP immunoreactivity Fine spongiform degeneration and astrogliosis; punctate PrP immunoreactivity; substantia nigra not affected No spongiform degeneration and PrP immunoreactivity
MM 19 kDa (type 2) Residue 97
MM 21 kDa (type 1) Residue 82
a,b
Clinical features Mean age at death Median duration of illness Neurological signs
General diagnostic testa Thalamic MRI high signal EEG PrPSc detection in tonsil biopsy Neuropathological featuresb,c Cerebral and cerebellar cortex
Caudate nucleus and putamen Posterior thalamic nuclei and midbrain Brainstem and spinal cord Molecular features of PrPSc 129 Polymorphism Gel mobility (type) N-terminal PK cleavage site a
Later stage: myoclonus, ataxia, and pyramidal signs
Will RG and Ward HJ (2004) Clinical features of variant Creutzfeldt–Jakob disease. Current Topics in Microbiology and Immunology 284: 121–132. b Gambetti P, et al. (2003)Sporadic and familial CJD: Classification and characterisation. British Medical Bulletin 66: 213–239. c Ironside JW and Head MW (2004) Neuropathology and molecular biology of variant Creutzfeldt–Jakob disease Current Topics in Microbiology and Immunology 284: 133–159. Source EEG, Electroencephalogram.
Variant Creutzfeldt–Jakob Disease
manifest early psychiatric disorders such as depression, anxiety, and withdrawal. About 6 months later, neurologic disorders emerge, including cognitive impairment, ataxia, and involuntary movements. Chorea, dystonia, and myoclonus are also observable. During the progressive clinical course, dementia and diffuse cortical deficits are predictable. Finally, patients are mute and bed-bound. Death is inevitable after a median of 14 months from the onset of symptoms (range, 6–39 months), largely due to an intercurrent infection such as respiratory infection. It is recommended that the combination of an affective or psychotic disorder with persistent pain, sensory symptoms, gait ataxia, or dysarthria should signal a diagnosis of vCJD, especially in younger patients. Unlike sCJD, 14–3–3 protein in the cerebrospinal fluid, the electroencephalogram and CT brain scan are less helpful in diagnosing vCJD because these are usually normal. However, an MRI scan may be helpful. For example, specific high signal in the posterior thalamus on T2-weighted images can be detected in over 75% of vCJD cases. Moreover, the sensitivity of an MRI brain scan in vCJD can be improved by fluid-attenuated inversion recovery (FLAIR). The definite diagnosis of vCJD requires neuropathologic examination of brain tissue obtained either at biopsy or autopsy. In 2000, Will and colleagues established the diagnostic criteria, by which accurate antemortem diagnosis can be achieved using a combination of clinical history with special investigations including tonsil biopsy using PrP immunohistochemistry and Western blotting, as well as MRI brain scan.
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neuroblastoma cells. A recent patient-preference trial on all forms of CJD showed acceptable level of tolerance but no effect on the clinical course of CJD. Flupirtine maleate, a centrally acting nonopioid analgesic, has been tested in a randomized double-blind study of subjects with the diagnosis of probable CJD. Treated patients showed significantly slower rate of cognitive deterioration but no significant difference in survival time. Pentosan polysulfate (PPS), a drug for the treatment of interstitial cystitis, has been reported to stabilize and delay the progression of prion disease but there are controversial results in clinical studies. A major problem is that PPS does not cross the blood–brain barrier and it has to be administered intraventricularly. To date, this compound has not been tested in any case-control study. Administration of doxycyclin, a member of the tetracycline group, to sCJD patients under compassionate treatment has been reported to more than double survival rate compared to untreated sCJD subjects. A phase II, multicenter, randomized, double-blind study is ongoing.
Acknowledgments The authors want to thank Dr. Pierluigi Gambetti for providing Fig. 1 and Dr. James Ironside for providing vCJD samples. Supported by the CJD Foundation, NIH R01 NS062787, NIA AG-14359, CDC UR8/ CCU515004, and Charles S. Britton Fund. See also: Ataxia; Creutzfeldt–Jacob Disease; Kuru.
Differential Diagnosis For suspect vCJD cases, the main differential diagnosis lies with other human prion diseases, especially sCJD. Sporadic CJD can be readily excluded if detailed clinical data are available and special investigations are included following Will et al. diagnostic criteria. A detailed differential diagnosis between sCJDMM1 (the most common subtype of sCJD) and vCJD, including pathology, is listed in Table 2.
Management and Prognosis Although scrapie in sheep and goats has been recognized for more than 200 years and the first CJD case in humans was identified almost 90 years ago, to date no effective treatment has been found. Many attempts to treat experimental prion diseases in animals have been made over the past 30 years but only a few therapeutic compounds have been tested in patients, and none of them have been found effective in treating human prion diseases. The following compounds have being studied in clinic. Quinacrine, a widely used antimalarial drug, was found to successfully block formation of PrPSc in infected mouse
Further Reading Aguzzi A, Baumann F, and Bremer J (2008) The prion’s elusive reason for being. Annual Review of Neuroscience 31: 439–477. Brandel JP, et al. (2009) Variant Creutzfeldt–Jakob disease in France and the United Kingdom: Evidence for the same agent strain. Annals of Neurology 65(3): 249–256. Collinge J, Sidle KCL, Meads J, Ironside J, and Hill AF (1996) Molecular analysis of prion strain variation and the aetiology of ‘new variant’ CJD. Nature 383: 685–690. Gambetti P, Kong Q, Zou W, Parchi P, and Chen SG (2003) Sporadic and familial CJD: Classification and characterisation. British Medical Bulletin 66: 213–239. Glatzel M, Giger O, Braun N, and Aguzzi A (2004) The peripheral nervous system and the pathogenesis of prion diseases. Current Molecular Medicine 4: 355–359. Haı¨k S, Faucheux BA, Sazdovitch V, et al. (2003) The sympathetic nervous system is involved in variant Creutzfeldt–Jakob disease. Nature Medicine 9: 1121–1123. Head MW, Ritchie D, Smith N, et al. (2004) Peripheral tissue involvement in sporadic, iatrogenic, and variant Creutzfeldt–Jakob disease: An immunohistochemical, quantitative, and biochemical study. The American Journal of Pathology 164: 143–153. Hill AF, Butterworth RJ, Joiner S, et al. (1999) Investigation of variant Creutzfeldt–Jakob disease and other human prion diseases with tonsil biopsy samples. Lancet 353: 183–189. Hill AF, Desbruslais M, Joiner S, et al. (1997) The same prion strain causes vCJD and BSE. Nature 389: 448–450.
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Ironside JW, Bishop MT, Connolly K, et al. (2006) Variant Creutzfeldt–Jakob disease: Prion protein genotype analysis of positive appendix tissue samples from a retrospective prevalence study. British Medical Journal 332: 1186–1188. Ironside JW and Head MW (2004) Neuropathology and molecular biology of variant Creutzfeldt–Jakob disease. Current Topics in Microbiology and Immunology 284: 133–159. Peden AH, Head MW, Ritchie DL, Bell JE, and Ironside JW (2004) Preclinical vCJD after blood transfusion in a PRNP codon 129 heterozygous patient. Lancet 364: 527–529. Prusiner SB (1998) Prions. Proceedings of the National Academy of Sciences of the United States of America 95: 13363–13383. Spencer MD, Knight RS, and Will RG (2002) First hundred cases of variant Creutzfeldt–Jakob disease: Retrospective case note review of early psychiatric and neurological features. British Medical Journal 324: 1479–1482. Trevitt CR and Collinge J (2006) A systematic review of prion therapeutics in experimental models. Brain 129: 2241–2265. Wadsworth JD, Joiner S, Hill AF, et al. (2001) Tissue distribution of protease resistant prion protein in variant Creutzfeldt–Jakob disease using a highly sensitive immunoblotting assay. Lancet 358: 171–180. Ward HJ, Head MW, Will RG, and Ironside JW (2003) Variant Creutzfeldt–Jakob disease. Clinics in Laboratory Medicine 23: 87–108. Westergard L, Christensen HM, and Harris DA (2007) The cellular prion protein (PrPC): Its physiological function and role in disease. Biochimica Et Biophysica Acta 1772: 629–644. Will RG, Ironside JW, Zeidler M, et al. (1996) A new variant of Creutzfeldt–Jakob disease in the UK. Lancet 347: 921–925.
Will RG and Ward HJ (2004) Clinical features of variant Creutzfeldt–Jakob disease. Current Topics in Microbiology and Immunology 284: 121–132. Will RG, Zeidler M, Stewart GE, et al. (2000) Diagnosis of new variant Creutzfeldt–Jakob disease. Annals of Neurology 47: 575–582. Zeidler M and Ironside JW (2000) The new variant of Creutzfeldt–Jakob disease. Revue Scientifique Et Technique 19: 98–120. Zou WQ and Gambetti P (2007) Prion: The chameleon protein. Cellular and Molecular Life Sciences 64: 3266–3270. Zou WQ and Gambetti P (2009) Variant Creutzfeldt–Jakob disease in France and the United Kingdom: Evidence for the same agent strain. Annals of Neurology 65(3): 233–235.
Relevant Websites http://www.cjdsurveillance.com/ – CJD Surveillance National Prion Disease Pathology Surveillance Center. http://www.cdc.gov/ – Centers for Disease Control and Prevention. http://www.cjd.ed.ac.uk/ – The National Creutzfeldt-Jakob Disease Surveillance Unit (NCJDSU). http://www.eurocjd.ed.ac.uk/ – The European and Allied Countries Collaborative Study Group of CJD (EUROCJD) plus the Extended European Collaborative Study Group of CJD (NEUROCJD). http://www.who.int/ – World Health Organization.
Glossary Ataxia – Inability to coordinate voluntary movements, leading to unsteady movements and staggering gait; most often associated with lesions of the cerebellum. Bovine spongiform encephalopathy (BSE) – A prion disease of cattle; the bovine prions are transmitted to humans through consumption of contaminated meat products, and lead to variant Creutzfeldt–Jacob Disease (vCJD). Cellular prion protein (PrPC) – A normal glycoprotein attached to the cell surface through a glycosylphosphatidylinositol (GPI) anchor most abundant in the brain but also in other organs. Myoclonus – A sudden twitching of muscles or parts of muscles, without rhythm or pattern. Psychiatric symptoms – Early symptoms frequently seen in vCJD including depression, anxiety, and withdrawal. Scrapie prion protein (PrPSc) – An infectious and pathogenic protein also called prion that derives from PrPC via a structural transition from a-helix into b-sheet. In sharp contrast to PrPC, PrPSc is detergent-insoluble, resistant to protease, prone to aggregation, and infectious. Variant Creutzfeldt–Jakob disease (vCJD) – A variant form of Creutzfeldt–Jakob disease acquired from the consumption of BSE-contaminated meat. It is characterized by young age at onset; early dominant psychiatric symptoms followed by neurologic deficits (cerebellar ataxia, involuntary movements, dystonia, and myoclonus); abundant florid prion plaques; and PK-resistant PrPSc in the brain.
Definition and History Variant Creutzfeldt–Jakob disease (vCJD) belongs to a group of highly heterogeneous and fatal transmissible spongiform encephalopathies, or prion diseases, that affect both animals and humans. Animal prion diseases include scrapie in sheep and goats, bovine spongiform encephalopathy (BSE or mad cow disease) in cattle, as well as chronic wasting disease in deer and elk. In humans, prion diseases can be sporadic, inherited, or acquired by infection, depending on their etiology. They mainly manifest four major phenotypes: CJD, Gerstmann–Stra¨ussler–Scheinker disease, kuru, and fatal familial insomnia. As a group, prion diseases are characterized clinically by disorders of cognition and movement; pathologically by spongiform degeneration, neuronal loss, and astrocytosis; and biochemically by deposition of an infectious proteinaceous pathogen called prion or scrapie prion protein (PrPSc). In addition to these basic characteristics, vCJD also possesses a unique identity: early dominant psychiatric symptoms followed by late neurologic deficits, young age at death, presence in the brain of florid prion plaques, and an abnormal PrP that is resistant to protease digestion and displays distinctive electrophoretic characteristics (Figure 1). vCJD was first discovered by Will and colleagues in the United Kingdom in 1996. Its discovery, together with the immediate demonstration of the causal link between vCJD and BSE, represent milestones in the history of prion disease. Not only did these findings demonstrate, for the first time, that prion disease could be transmitted from animals to humans, but they also greatly accelerated the establishment of surveillance and control of prion diseases. Following the outbreak of BSE, the surveillance of CJD was heightened in the United Kingdom in 1990 in order to monitor any changes in this condition that might be associated with transmission of BSE to humans. Subsequently,
315
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(a)
(b)
kDa
Di.Mono.-
-21 -19
Un.Type 1 Type 2 Type 2 (c)
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sCJD
vCJD
Figure 1 PrPSc detection by immunohistochemistry and Western Blot analysis. Immunohistochemistry of brains affected by vCJD (a) and sCJD (b), and of a normal brain (c) with anti-PrP antibody 3F4. Amount and pattern of distribution of PrPSc are different between vCJD, where PrPSc forms clumps, and sCJD, which shows dot-like formations. No PrP is seen in the normal brain (J. Ironside, National CJD Surveillance Center, Edinburgh, UK, and P. Gambetti, National Prion Disease Pathology Surveillance Center, Cleveland, OH, USA). Probed with 3F4 (d) Homogenates of the frontal cortex from sCJDMM1 (type 1), sCJDMM2 (type 2) and vCJD were treated with proteinase K (PK) prior to Western blotting with 3F4 antibody. The PK-resistant PrP core fragments from sCJD exhibit a dominant middle band corresponding to monoglycosylated PrP and a lower band corresponding to unglycosylated PrP migrating at 21 kDa (PrPSc type 1) or at 19 kDa (PrPSc type 2). In contrast, the PK-resistant PrP core fragments from all vCJD show a single uniform profile: a dominant upper band corresponding to diglycosylated PrP and a lower band migrating at 19 kDa. Di.: diglycosylated PrP; Mono.: monoglycosylated PrP; and Un.: unglycosylated PrP.
in 1993, the European Union started a project involving the majority of European countries (extended to all member states in 1998) in which common methodologies and criteria for case definition were adopted. In 1995 and early 1996, through these efforts a number of cases of CJD were identified in the United Kingdom with a unique phenotype distinct from sporadic CJD. By March 1996, ten cases of CJD sharing a very similar phenotype had been collected: the patients were of a young age at death (mean 29 years vs. 66 years in sporadic CJD); and the illness was characterized by long duration (mean 14 months vs. 4.5 months in sporadic CJD) and an unusual and remarkably uniform clinical presentation, distinct from that previously seen in CJD. Subsequent animal inoculation studies confirmed that this novel human prion disease is caused by the same prion strain that causes BSE in cattle.
Pathogenesis vCJD, along with kuru of New Guinea, and iatrogenic CJD, are the three forms of the disease known to date to be acquired by infection. However, unlike kuru and iatrogenic CJD (caused, respectively, by human-to-human transmission through ritual cannibalism, or medical and surgical procedures), vCJD is caused by transmission from cattle,
most likely through an oral route by consumption of prioncontaminated meat products, or possibly through parenteral routes. In addition to the acquired form, the other forms of prion diseases comprise sporadic CJD, the most common form and genetically determined or familial CJD. However, regardless of their distinct etiologies, all prion diseases share a fundamental pathogenetic mechanism: the conversion of the normal or cellular PrP (PrPC) into an isoform, identified as scrapie PrP (PrPSc). PrPSc is the only known component of prion that is believed to be pathogenic and infectious but at the same time (and in contrast to viruses and bacteria) is thought to be free of nucleic acids. It is postulated that in acquired prion diseases, including vCJD, prions are acquired by exogenous infection whereas in sporadic and familial CJD prions form spontaneously, either as a result of a random misfolding event or as a result of the presence of PrP destabilizing mutation. Most of PrPC is full-length, diglycosylated, and attached to the cell surface via a glycosylphosphatidylinisotol (GPI) anchor; but small amounts of PrPC may be N-terminally truncated, monoglycosylated or unglycosylated, anchorless, or cytosolic. PrPC and PrPSc share their primary structure. The critical difference between these two proteins lies in the conformation, in that PrPC converts into PrPSc through an a-helix to b-sheet structural transition which results in profound differences in the physicochemical and biological
Variant Creutzfeldt–Jakob Disease
properties of the two conformers. PrPSc is rich in b-sheets and is detergent-insoluble, multimeric, resistant to proteinase K (PK) treatment, and infectious. In contrast, PrPC is rich in a-helix, detergent-soluble, monomeric, sensitive to PK, and noninfectious. Although there is no doubt that the coexistence of PrPSc and PrPC in the central nervous system (CNS) is a prerequisite for prion diseases, the role of these two PrP conformers in the pathogenesis of prion disease is not completely understood. Two major hypotheses have been proposed to explain how changes in PrPC conformation could cause neurodegeneration: first, functional gain, in which prion pathology is attributable to the acquisition of toxic function; and second, functional loss, in which a PrPC physiologic activity is lost upon conversion to or interaction with PrPSc. A Single Uniform Prion Strain Based on gel mobility and glycoform ratio, PrPSc detected in sCJD can be divided into two types: PrPSc type 1 with an unglycosylated PrP migrating at 21 kDa and a dominant N-terminal protease cleavage site at residue 82; and PrPSc type 2 with an unglycosylated PrP migrating at 19 kDa and a cleavage site at residue 97 on the gel (Figure 1). Moreover, all PrPSc species from sCJD exhibit a dominant monoglycosylated PrP. In contrast, PrPSc from all vCJD examined so far is invariably of a dominant diglycosylated PrP and a 19-kDa unglycosylated PrP with a primary cleavage site at residue 97 (Figure 1). The electrophoretic profile of PrPSc detected in all vCJD cases is virtually identical to that found in BSE, which indeed implies that prion present in vCJD derives from BSE. Polymorphism at Residue 129 of PrP It has been believed that polymorphism at residue 129 of PrP (either methionine (M) or valine (V)) is associated with susceptibility to human prion. Although most sporadic CJD occurs in individuals homozygous for 129 MM, it also affects individuals with genotype 129 MV or 129 VV. Remarkably, all clinically affected vCJD cases studied so far have been 129 MM homozygous. However, the identification, in an anonymous screening study, of two positive appendix tissues from subjects with 129 VV genotype, together with the description of an asymptomatic case of vCJD in an 129 MV patient infected by blood transfusion, highlight the possibility that polymorphisms rather than 129 MM could also be susceptible to variant CJD although they might exhibit atypical phenotypes such as a subclinical form. Involvement of the Lymphoreticular System The distinctive pathogenesis of vCJD in comparison with other forms of CJD is also reflected in the involvement of
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the lymphoreticular system. PrPSc is readily detectable in lymphoreticular tissues in vCJD including gut-associated lymphoid tissue, tonsil, spleen, appendix, and lymph nodes, whereas it is only detected in the spleen of some sporadic CJD using highly sensitive methods. Prion neuroinvasion bears remarkable similarities to neuroinvasion by viral agents. Oral or Parenteral Transmission Route Presumably, all clinically infected vCJD cases are contracted orally, through consumption of contaminated meat products derived from BSE cattle. But exactly how the BSE prion spreads from the gastrointestinal system to the CNS remains an unresolved question. It has been hypothesized that the invading prions undergo two phases to reach the CNS: they accumulate and replicate in the lymphoreticular organs (primary phase) and then disseminate to the CNS through the peripheral nerves. Studies in prion-infected animals revealed that the autonomous nervous system, including both vagal and sympathetic nerve fibers, contributes to the spread of orally administered prions. These results are consistent with a finding that PrPSc is detected in the sympathetic nervous system (stellate and celiac ganglia) in vCJD but not in sCJD. In addition to the oral route, recent identification of three cases of transfusion-associated vCJD prion infection has raised significant concerns that there may be substantial risks of iatrogenic transmission of vCJD prions. Surprisingly, an asymptomatic transfusionassociated vCJD case exhibited MV polymorphism at residue 129 but no neurologic disorders and no prion-related neuropathologic changes. Moreover, PrPSc was detectable only in the lymphoreticular tissues but not in the brain. It is unclear whether this preclinical stage resulted from the parenteral route transmission or from the 129 MV heterozygous polymorphism.
Epidemiology and Risk Factors Variant CJD has been reported in many countries particularly in Europe. As of February 2009, 214 cases of vCJD have been identified worldwide, mostly in the United Kingdom (Table 1). The patients in Ireland, Canada, and the United States of America had spent significant periods of time in the United Kingdom, which suggests that these patients contracted the disease through dietary exposure to BSE in the United Kingdom. However, the Italian patient and most French patients had not visited the United Kingdom. How were these patients infected by the BSE prion? Brandel and colleagues recently conducted a study in which they demonstrated that the British and French vCJD cases manifested very similar clinical, histopathologic, and molecular features and concluded that the two sets of vCJD patients shared the same
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prion strain. These findings highlight two issues. First, they raise the question of the origin of the infectious prion in the French vCJD: whether it originates from British BSE or from indigenous French BSE; and second, Table 1 disease
Number of vCJD reported and countries with the
Country
Number of cases
Unite Kingdom France Spain Republic of Ireland United States of America The Netherlands Portugal Saudi Arabia Italy Canada Japan Total
169 23 5 4 3 3 2 2 1 1 1 214
Data as of February 2009. Quoted from the European and Allied Countries Study Group of CJD (EUROCJD). Table 2
whether vCJD worldwide is caused by one prion strain or whether all vCJD cases carry the same British prion strain. It is critical that these two issues be clarified, so that the diffusion of the BSE epidemics through different continents can be understood and arrested.
Clinical Features, Diagnostic Work-Up and Tests, and Diagnostic Criteria It is widely believed that the high heterogeneity of sporadic CJD results mainly from the chameleon-like conformation of prions. Indeed, at least five clinical subtypes of sCJD have been identified based on a combination of PrPSc types and PrP polymorphism at residue 129. Surprisingly, the clinical manifestations of vCJD linked to a single uniform prion strain (PrPSc type 2 with the homozygous MM) remain relatively heterogeneous (Table 2). According to an analysis of clinical features of the first 100 cases by Will and colleagues, 63% of cases present with psychiatric symptoms alone, 15% with isolated neurologic symptoms and 22% with mixed features. Patients with vCJD usually
Differences between variant and sporadic CJD Variant CJD
Typical sporadic CJD (MM1)
29 years 14 months Presentation: affective or psychotic disorder, persistent pain, sensory symptoms, sometimes gait ataxia or dysarthria Later stage: ataxia, dementia
65 years 4 months Presentation: cognitive impairment, ataxia, mental, and visual signs
Pulvinar 90% ‘Typical’ 0% Positive
Caudate/putamen 60% ‘Typical’ 80% Negative
Multiple florid plaques in H&E sections, numerous small clusters of plaques in PrP stained sections, amorphous pericellular and perivascular PrP accumulation Severe spongiform change, perineuronal and axonal PrP accumulation Marked astrocytosis and neuronal loss
Reticular and perineuronal PrP accumulation in gray matter
Widespread fine spongiform degeneration, astrogliosis, neuronal loss; punctate PrP immunoreactivity; ‘brush stroke’ pattern in cerebellar molecular layer Fine spongiform degeneration and astrogliosis; punctate PrP immunoreactivity Fine spongiform degeneration and astrogliosis; punctate PrP immunoreactivity; substantia nigra not affected No spongiform degeneration and PrP immunoreactivity
MM 19 kDa (type 2) Residue 97
MM 21 kDa (type 1) Residue 82
a,b
Clinical features Mean age at death Median duration of illness Neurological signs
General diagnostic testa Thalamic MRI high signal EEG PrPSc detection in tonsil biopsy Neuropathological featuresb,c Cerebral and cerebellar cortex
Caudate nucleus and putamen Posterior thalamic nuclei and midbrain Brainstem and spinal cord Molecular features of PrPSc 129 Polymorphism Gel mobility (type) N-terminal PK cleavage site a
Later stage: myoclonus, ataxia, and pyramidal signs
Will RG and Ward HJ (2004) Clinical features of variant Creutzfeldt–Jakob disease. Current Topics in Microbiology and Immunology 284: 121–132. b Gambetti P, et al. (2003)Sporadic and familial CJD: Classification and characterisation. British Medical Bulletin 66: 213–239. c Ironside JW and Head MW (2004) Neuropathology and molecular biology of variant Creutzfeldt–Jakob disease Current Topics in Microbiology and Immunology 284: 133–159. Source EEG, Electroencephalogram.
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manifest early psychiatric disorders such as depression, anxiety, and withdrawal. About 6 months later, neurologic disorders emerge, including cognitive impairment, ataxia, and involuntary movements. Chorea, dystonia, and myoclonus are also observable. During the progressive clinical course, dementia and diffuse cortical deficits are predictable. Finally, patients are mute and bed-bound. Death is inevitable after a median of 14 months from the onset of symptoms (range, 6–39 months), largely due to an intercurrent infection such as respiratory infection. It is recommended that the combination of an affective or psychotic disorder with persistent pain, sensory symptoms, gait ataxia, or dysarthria should signal a diagnosis of vCJD, especially in younger patients. Unlike sCJD, 14–3–3 protein in the cerebrospinal fluid, the electroencephalogram and CT brain scan are less helpful in diagnosing vCJD because these are usually normal. However, an MRI scan may be helpful. For example, specific high signal in the posterior thalamus on T2-weighted images can be detected in over 75% of vCJD cases. Moreover, the sensitivity of an MRI brain scan in vCJD can be improved by fluid-attenuated inversion recovery (FLAIR). The definite diagnosis of vCJD requires neuropathologic examination of brain tissue obtained either at biopsy or autopsy. In 2000, Will and colleagues established the diagnostic criteria, by which accurate antemortem diagnosis can be achieved using a combination of clinical history with special investigations including tonsil biopsy using PrP immunohistochemistry and Western blotting, as well as MRI brain scan.
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neuroblastoma cells. A recent patient-preference trial on all forms of CJD showed acceptable level of tolerance but no effect on the clinical course of CJD. Flupirtine maleate, a centrally acting nonopioid analgesic, has been tested in a randomized double-blind study of subjects with the diagnosis of probable CJD. Treated patients showed significantly slower rate of cognitive deterioration but no significant difference in survival time. Pentosan polysulfate (PPS), a drug for the treatment of interstitial cystitis, has been reported to stabilize and delay the progression of prion disease but there are controversial results in clinical studies. A major problem is that PPS does not cross the blood–brain barrier and it has to be administered intraventricularly. To date, this compound has not been tested in any case-control study. Administration of doxycyclin, a member of the tetracycline group, to sCJD patients under compassionate treatment has been reported to more than double survival rate compared to untreated sCJD subjects. A phase II, multicenter, randomized, double-blind study is ongoing.
Acknowledgments The authors want to thank Dr. Pierluigi Gambetti for providing Fig. 1 and Dr. James Ironside for providing vCJD samples. Supported by the CJD Foundation, NIH R01 NS062787, NIA AG-14359, CDC UR8/ CCU515004, and Charles S. Britton Fund. See also: Ataxia; Creutzfeldt–Jacob Disease; Kuru.
Differential Diagnosis For suspect vCJD cases, the main differential diagnosis lies with other human prion diseases, especially sCJD. Sporadic CJD can be readily excluded if detailed clinical data are available and special investigations are included following Will et al. diagnostic criteria. A detailed differential diagnosis between sCJDMM1 (the most common subtype of sCJD) and vCJD, including pathology, is listed in Table 2.
Management and Prognosis Although scrapie in sheep and goats has been recognized for more than 200 years and the first CJD case in humans was identified almost 90 years ago, to date no effective treatment has been found. Many attempts to treat experimental prion diseases in animals have been made over the past 30 years but only a few therapeutic compounds have been tested in patients, and none of them have been found effective in treating human prion diseases. The following compounds have being studied in clinic. Quinacrine, a widely used antimalarial drug, was found to successfully block formation of PrPSc in infected mouse
Further Reading Aguzzi A, Baumann F, and Bremer J (2008) The prion’s elusive reason for being. Annual Review of Neuroscience 31: 439–477. Brandel JP, et al. (2009) Variant Creutzfeldt–Jakob disease in France and the United Kingdom: Evidence for the same agent strain. Annals of Neurology 65(3): 249–256. Collinge J, Sidle KCL, Meads J, Ironside J, and Hill AF (1996) Molecular analysis of prion strain variation and the aetiology of ‘new variant’ CJD. Nature 383: 685–690. Gambetti P, Kong Q, Zou W, Parchi P, and Chen SG (2003) Sporadic and familial CJD: Classification and characterisation. British Medical Bulletin 66: 213–239. Glatzel M, Giger O, Braun N, and Aguzzi A (2004) The peripheral nervous system and the pathogenesis of prion diseases. Current Molecular Medicine 4: 355–359. Haı¨k S, Faucheux BA, Sazdovitch V, et al. (2003) The sympathetic nervous system is involved in variant Creutzfeldt–Jakob disease. Nature Medicine 9: 1121–1123. Head MW, Ritchie D, Smith N, et al. (2004) Peripheral tissue involvement in sporadic, iatrogenic, and variant Creutzfeldt–Jakob disease: An immunohistochemical, quantitative, and biochemical study. The American Journal of Pathology 164: 143–153. Hill AF, Butterworth RJ, Joiner S, et al. (1999) Investigation of variant Creutzfeldt–Jakob disease and other human prion diseases with tonsil biopsy samples. Lancet 353: 183–189. Hill AF, Desbruslais M, Joiner S, et al. (1997) The same prion strain causes vCJD and BSE. Nature 389: 448–450.
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Ironside JW, Bishop MT, Connolly K, et al. (2006) Variant Creutzfeldt–Jakob disease: Prion protein genotype analysis of positive appendix tissue samples from a retrospective prevalence study. British Medical Journal 332: 1186–1188. Ironside JW and Head MW (2004) Neuropathology and molecular biology of variant Creutzfeldt–Jakob disease. Current Topics in Microbiology and Immunology 284: 133–159. Peden AH, Head MW, Ritchie DL, Bell JE, and Ironside JW (2004) Preclinical vCJD after blood transfusion in a PRNP codon 129 heterozygous patient. Lancet 364: 527–529. Prusiner SB (1998) Prions. Proceedings of the National Academy of Sciences of the United States of America 95: 13363–13383. Spencer MD, Knight RS, and Will RG (2002) First hundred cases of variant Creutzfeldt–Jakob disease: Retrospective case note review of early psychiatric and neurological features. British Medical Journal 324: 1479–1482. Trevitt CR and Collinge J (2006) A systematic review of prion therapeutics in experimental models. Brain 129: 2241–2265. Wadsworth JD, Joiner S, Hill AF, et al. (2001) Tissue distribution of protease resistant prion protein in variant Creutzfeldt–Jakob disease using a highly sensitive immunoblotting assay. Lancet 358: 171–180. Ward HJ, Head MW, Will RG, and Ironside JW (2003) Variant Creutzfeldt–Jakob disease. Clinics in Laboratory Medicine 23: 87–108. Westergard L, Christensen HM, and Harris DA (2007) The cellular prion protein (PrPC): Its physiological function and role in disease. Biochimica Et Biophysica Acta 1772: 629–644. Will RG, Ironside JW, Zeidler M, et al. (1996) A new variant of Creutzfeldt–Jakob disease in the UK. Lancet 347: 921–925.
Will RG and Ward HJ (2004) Clinical features of variant Creutzfeldt–Jakob disease. Current Topics in Microbiology and Immunology 284: 121–132. Will RG, Zeidler M, Stewart GE, et al. (2000) Diagnosis of new variant Creutzfeldt–Jakob disease. Annals of Neurology 47: 575–582. Zeidler M and Ironside JW (2000) The new variant of Creutzfeldt–Jakob disease. Revue Scientifique Et Technique 19: 98–120. Zou WQ and Gambetti P (2007) Prion: The chameleon protein. Cellular and Molecular Life Sciences 64: 3266–3270. Zou WQ and Gambetti P (2009) Variant Creutzfeldt–Jakob disease in France and the United Kingdom: Evidence for the same agent strain. Annals of Neurology 65(3): 233–235.
Relevant Websites http://www.cjdsurveillance.com/ – CJD Surveillance National Prion Disease Pathology Surveillance Center. http://www.cdc.gov/ – Centers for Disease Control and Prevention. http://www.cjd.ed.ac.uk/ – The National Creutzfeldt-Jakob Disease Surveillance Unit (NCJDSU). http://www.eurocjd.ed.ac.uk/ – The European and Allied Countries Collaborative Study Group of CJD (EUROCJD) plus the Extended European Collaborative Study Group of CJD (NEUROCJD). http://www.who.int/ – World Health Organization.