Classification of sporadic Creutzfeldt-Jakob disease based on molecular and phenotypic analysis of 300 subjects

Classification of Sporadic Creutzfeldt-JakobDisease Based on Molecular and Phenotypic

Analysis of 300 SubjectsPiero Parchi, MD,* Armin Giese, MD,† Sabina Capellari, MD,* Paul Brown, MD,‡

Walter Schulz-Schaeffer, MD,† Otto Windl, PhD,† Inga Zerr, MD,§ Herbert Budka, MD,i

Nicolas Kopp, MD,¶ Pedro Piccardo, MD,# Sigrid Poser, MD,§ Amyn Rojiani, MD, PhD,**Nathalie Streichemberger, MD,¶ Jean Julien, MD,†† Claude Vital, MD,‡‡ Bernardino Ghetti, MD,#

Pierluigi Gambetti, MD,* and Hans Kretzschmar, MD†

Phenotypic heterogeneity in sporadic Creutzfeldt-Jakob disease (sCJD) is well documented, but there is not yet a sys-tematic classification of the disease variants. In a previous study, we showed that the polymorphic codon 129 of theprion protein gene (PRNP), and two types of protease-resistant prion protein (PrPSc) with distinct physicochemicalproperties, are major determinants of these variants. To define the full spectrum of variants, we have examined a seriesof 300 sCJD patients. Clinical features, PRNP genotype, and PrPSc properties were determined in all subjects. In 187, wealso studied neuropathological features and immunohistochemical pattern of PrPSc deposition. Seventy percent of sub-jects showed the classic CJD phenotype, PrPSc type 1, and at least one methionine allele at codon 129; 25% of casesdisplayed the ataxic and kuru-plaque variants, associated to PrPSc type 2, and valine homozygosity or heterozygosity atcodon 129, respectively. Two additional variants, which included a thalamic form of CJD and a phenotype characterizedby prominent dementia and cortical pathology, were linked to PrPSc type 2 and methionine homozygosity. Finally, a rarephenotype characterized by progressive dementia was linked to PrPSc type 1 and valine homozygosity. The present datademonstrate the existence of six phenotypic variants of sCJD. The physicochemical properties of PrPSc in conjunctionwith the PRNP codon 129 genotype largely determine this phenotypic variability, and allow a molecular classification ofthe disease variants.

Parchi P, Giese A, Capellari S, Brown P, Schulz-Schaeffer W, Windl O, Zerr I, Budka H, Kopp N, Piccardo P,Poser S, Rojiani A, Streichemberger N, Julien J, Vital C, Ghetti B, Gambetti P, Kretzschmar H.

Classification of sporadic Creutzfeldt-Jakob disease based on molecular and phenotypic analysisof 300 subjects. Ann Neurol 1999;46:224–233

Creutzfeldt-Jakob disease (CJD) has attracted increas-ing attention because of the unique properties of theinfectious agent and the emergence of bovine spongi-form encephalopathy (BSE), which reached epidemicproportion in the past decade.1,2 It appears that theBSE agent can be transmitted to the human popula-tion causing a new variant of CJD (nvCJD), with dis-tinct neuropathological and biochemical characteris-tics.3–6 The identification of nvCJD has reinforced theneed for a detailed analysis of phenotypic variability ofall forms of CJD, including the more common spo-radic form (sCJD). Distinctive clinical and pathologicalfeatures in small groups of sCJD patients have been

described, but there is not yet a systematic classificationof the disease variants.7–11 Moreover, the fundamentalquestion as to what extent phenotypic variability is de-termined by host genetic factors rather than by distinctstrains of the agent has not been addressed.

The pathogenesis of prion diseases is related to thecerebral deposition of a pathological isoform of theprion protein (PrP), a host-encoded, membrane-associated, copper-binding glycoprotein.12–14 Thepathological isoform of PrP (PrPSc) is formed througha posttranslational event involving conformationalchanges of the normal cellular isoform of the prionprotein (PrPC).15,16 PrPSc differs from PrPC by its high

From the *Division of Neuropathology, Institute of Pathology, CaseWestern Reserve University, Cleveland, OH; Departments of §Neu-rology and †Neuropathology, Georg-August-University, Gottingen,Germany; ‡Laboratory of CNS Studies, NINDS, National Institutesof Health, Bethesda, MD; iInstitute of Neurology, University of Vi-enna, and Austrian Reference Center for Human Prion Diseases,Vienna, Austria; ¶Hopital Neurologique Pierre Wertheimer, Lyon,and Departments of ††Neurology and ‡‡Pathology, Centre Hos-pitalier Universitaire Bordeaux, Pessac, France; #Department of

Pathology and Laboratory Medicine, Indiana University School ofMedicine, Indianapolis, IN; and **Department of Pathology, Uni-versity of South Florida, Tampa, FL.

Received Jan 28, 1999, and in revised form Mar 18. Accepted forpublication Mar 21, 1999.

Address correspondence to Dr Parchi, Division of Neuropathology,Institute of Pathology, Case Western Reserve University, 2085Adelbert Road, Cleveland, OH 44106.

224 Copyright © 1999 by the American Neurological Association

content in b-sheet structure and its partial resistance toprotease digestion.12,15,16 PrPSc is thought to be an es-sential, if not the exclusive, component of the trans-missible agent, or prion.17

Prions exist in many different strains that can be dis-tinguished by their disease characteristics after trans-mission to inbred animals.3,18–21 In addition, host ge-netic factors, mainly represented by polymorphisms ormutations in the coding region of the prion proteingene (PRNP), may also significantly affect the diseasephenotype.19 It has been recently shown that there areproperties of PrPSc, such as relative molecular mass andratio of di-, mono-, and unglycosylated forms of theprotein, that may allow the molecular identification ofprion strains.20,21 We showed that in sCJD two differ-ent types of PrPSc with distinct physicochemical prop-erties are found associated with distinct phenotypes,and suggested that two major prion strains are linked toCJD.22 In addition, we and others demonstrated an in-fluence on disease phenotype of a common methionine/valine (MV) polymorphism at codon 129 in thePRNP.22–25 To define the full spectrum of sCJD vari-ants, and contribute to the understanding of pathogen-esis and extent of strain variation in sCJD, we per-formed a detailed phenotypic and molecular analysis of300 sCJD patients. Based on these studies, which repre-sent the first comprehensive analysis of both molecularand clinicopathological features in a large series of pa-tients, we propose a classification of sCJD into six dis-tinct variants.

Patients and MethodsSelection of PatientsWe studied 300 subjects with confirmed CJD (PrPSc positiveon immunoblot), who lacked pathogenic mutations in thecoding region of PRNP and had a negative history of familialdiseases or exposure to known prion contaminants (pituitaryextracted hormones, intracerebral electrodes, and dura materor corneal grafts); 119 patients died in the United States be-tween 1990 and 1998, and 78 in Europe (Germany, 56;France, 15; Austria, 5; and Italy, 2) between 1993 and 1997.Forty cases (1997–1998) were from the National Prion Pa-thology Surveillance Center of the United States. The 56cases from Germany were part of the German National CJDSurveillance study. An additional 103 subjects belonged tothe National Institutes of Health series of transmitted cases26

and included 80 North American (USA, 77, Canada, 3) and23 European patients (France, 11; Italy, 4; UK, 4; Finland,3; Denmark, 1) who died between 1968 and 1980. Clinicaldata were available in all cases, and medical records alwaysincluded at least one neurological examination. Duration ofsymptoms was calculated from the time of presentation ofneurological signs suggesting an organic cause. Prodromalsymptoms were not considered. Clinical signs were classified“at onset” when observed within the first quarter of themean duration of symptoms of the group to which the pa-tient belonged (ie, 1 month if the mean duration was 4).

Histological ExaminationSemiquantitative evaluation of spongiosis, neuronal loss, andgliosis was performed in 187 brains by comparing hematox-ylin and eosin–stained sections from the affected subjects andfrom age-matched subjects with no history of neurologicaldisorders and no histopathological changes. Thirteen brainregions were examined (listed in Fig). Histological examina-tion was performed blindly to the results of molecular anal-ysis in most cases.

ImmunohistochemistryParaffin sections from formalin-fixed blocks of frontal (n 5165) and occipital cortices (n 5 110), as well as cerebellum(n 5 161) obtained from 187 brains, were processed by us-ing the monoclonal antibodies 3F427 and Go138 (Germancases),28 as described.29 PrP deposits were classified as (1)reticular or “synaptic,” (2) coarse or perivacuolar, and (3)plaque-like or focal.22,30

Molecular Genetic AnalysisGenomic DNA from all 300 subjects was used to amplifythe coding region of PRNP in the polymerase chain reactionwith the primers DG1 and DG222 or 895W and 896W(German patients).31 The polymerase chain reaction productwas visualized on a 1% agarose gel to detect potential inser-tion mutations or deletions. Potential point mutations wererevealed by the single-strand conformational polymorphismtechnique (German patients)31 or by the mutation mismatchdetection kit (Ambion, Inc, Austin, TX). Mutations werealso ruled out by direct sequencing of PRNP open readingframe in all cases of the rarest groups, who showed PrPSc

type 1 and valine homozygosity at codon 129 or PrPSc type2 and methionine homozygosity (see Results), and in at least3 subjects from the other groups. Finally, the codon 129genotype was examined by digestion with the restriction en-donuclease NspI in all subjects.

Protein StudiesImmunoblot analysis of PrPSc was performed as previouslydescribed.22 One or multiple samples from different brainregions, including the cerebral cortex (n 5 267), striatum(n 5 40), thalamus (n 5 27), or cerebellum (n 5 145) wereexamined in 275 subjects. In the remaining 25 (all from the1968–1980 period), the gray matter structure used for PrPSc

extraction was unidentifiable. The immunoblot profile ofPrPSc was classified as type 1 or type 2 based on electro-phoretic mobility, as previously described.22 For this analysis,PrPSc was resolved on 13% polyacrylamide gels, using aminigel apparatus (Mini-Protean II System, Bio-Rad, Her-cules, CA). For the analysis of PrPSc glycoform ratio, en-hanced chemiluminescence films were scanned at 42 mm res-olution and were analyzed quantitatively by using QuantityOne software (PDI, Imageware Systems, Huntington Sta-tion, NY).

ResultsMolecular AnalysisThe codon 129 allelic distribution in our sCJD popu-lation was significantly different from that reported for

Parchi et al: Spectrum of sCJD Variants 225

the normal European and US populations (Table1).31–34 Nearly 90% of patients were homozygous atcodon 129 with most having the genotype MM.

PrPSc involved two major patterns of electrophoreticmobility, with the relative molecular mass (Mr) of theunglycosylated band being either approximately 21 kd(type 1) or approximately 19 kd (type 2).22 We de-tected either one of the two PrPSc in all but 14 sub-jects, who showed both types (10 MM and four VVgenotypes). This association, however, was only de-tected in samples from the cerebral cortex, although itwas not limited to a specific cortical region. In the sub-cortical regions examined (at least one for each sub-ject), the 10 MM subjects only showed PrPSc type 1,the 4 VV subjects type 2. Finally, in most heterozygoussubjects (MV), PrPSc type 2 comprised a wider, moreheterogenous, unglycosylated band than in the ho-mozygotes. This band migrated at approximately 19 to20 kd, and was often visible as a doublet.

Type 1 and type 2 PrPSc were present in all PRNPgenotypes. However, most MM subjects showed PrPSc

type 1, whereas the VV and the MV patients predom-inantly displayed type 2 (see Table 1).

Three major bands that contain the diglycosylated,monoglycosylated, and unglycosylated isoforms, respec-tively, characterize the PrPSc profile on immunoblot.22

The relative proportion of each of these three bands(PrPSc glycoform ratio) showed a significant heteroge-neity among most of the sCJD groups (Table 2) de-fined by the codon 129 genotype and the type ofPrPSc. Most significantly, the analysis distinguishedtwo groups of MM2 subjects, designated as MM2-cortical (or MM2-C), and MM2-thalamic (or MM2-T), respectively, that also showed distinct phenotypicfeatures (see below).

Neuropathological and ImmunohistochemicalFindingsBy comparing lesion profiles and pattern of PrP immu-nostaining we identified six major pathological variants

that consistently recurred in at least 3 subjects. The sixsCJD variants largely correlated with the groups de-fined according to molecular criteria.

In the MM1 and MV1 subjects, a variable degree ofspongiform degeneration, gliosis, and loss of neuronsmainly affected the cerebral cortex, neostriatum, thala-mus, and cerebellum, whereas the hippocampus andthe brainstem nuclei were relatively spared (Fig). In thecerebral cortex, vacuolation was seen in all layers, andthe occipital lobe had the most severe pathology in47% of cases. Immunohistochemistry demonstratedthe synaptic pattern of PrPSc deposition in the cerebel-lum or cerebral cortex (Table 3). In addition, a coarsepattern was detected in about a third of subjects. Thispattern largely colocalized with large, confluent vacu-oles, and was most evident in the cerebral cortex. The10 MM subjects showing both PrPSc type 1 and 2 inthe cerebral cortex belonged to this subgroup.

VV1 subjects had predominant corticostriatal pa-thology with relative sparing of other subcortical struc-tures including the cerebellum (see Fig). No large con-fluent vacuoles were seen. Additional features were therelative sparing of the occipital lobe in comparisonwith the other cortical lobes, and the laminar corticaldistribution of spongiform changes that involved thedeeper layers. The latter, however, was clearly evidentonly in areas with preserved cytoarchitecture (ie, at bi-opsy). There were also ballooned neurons in the cere-bral cortex, that stained with antibodies to neurofila-ments, but not with glial fibrillary acidic protein, tau,a-synuclein, and ubiquitin antibodies. Immunohisto-chemistry for PrP only showed foci of very faint syn-aptic staining in the cerebral cortex, despite the severespongiform degeneration (see Table 3).

Two distinct phenotypes characterized the MM2subjects. In 6 (MM2-cortical), the lesion profile wassimilar to that of the MM1 group in all areas but thecerebellum, which lacked significant pathology (seeFig). Spongiform degeneration in these subjects con-sisted of large vacuoles, and was most severe in the ce-rebral cortex and striatum. Immunohistochemistry re-vealed a coarse staining pattern (see Table 3).

The other 6 MM2 subjects (MM2-thalamic) showedstriking similarities to the fatal familial insomnia phe-notype.35 Moderate to severe neuronal loss and gliosis,but no spongiform changes, were seen in most nucleiof the medial thalamus as well as in the inferior olives(see Fig). Spongiform degeneration was limited to iso-lated foci in the entorhinal cortex and cerebral neocor-tex. Immunohistochemistry showed a coarse pattern in1 case, and a faint synaptic staining in 2 subjects, butin the others the immunostaining was negative (seeTable 3).

All MV2 and VV2 subjects, including the 4 subjectsshowing both PrPSc types 1 and 2 in the cerebral cor-tex, displayed significant pathology in the limbic cor-

Table 1. Results (in %) of PRNP Genotyping andPrPSc Typing

Codon 129 MM MV VV

Normal populationa (n 5 544) 37 51 12sCJD population (n 5 300) 71.6b 11.7b 16.7b

PrPSc type 1 (n 5 214) 94.9c 3.7 1.4PrPSc type 2 (n 5 86) 14.0 31.4 54.6d

aValues obtained by combining the data published in references31–34.bp , 0.001 (x2 test) versus corresponding genotype in the normalpopulation.c,dInclude subjects with both type 1 and type 2 in the cortex.

PRNP 5 prion protein gene; PrPSc 5 protease-resistant prion pro-tein; sCJD 5 sporadic Creutzfeldt-Jakob disease.

226 Annals of Neurology Vol 46 No 2 August 1999

tex, and subcortical gray matter structures includingthe brainstem nuclei (see Fig). In contrast, the degreeof involvement of the neocortex correlated with theduration of symptoms, and it was relatively spared,particularly in the occipital lobe, in all subjects with adisease duration of less than 8 months. The corticalspongiform changes showed a laminar distribution in-volving the deeper layers. Immunohistochemistry re-

vealed a strong synaptic pattern showing a laminar dis-tribution in the cerebral cortex colocalized with thespongiform degeneration, plaque-like focal deposits,and strong staining along nerve fibers tracts andaround some neuronal perikarya and dendritic ar-borization (see Table 3).

Subjects MV2 could be further distinguished by thepresence of unicentric amyloid-kuru plaques in the cer-

Table 2. Glycoform Ratio (in %) of PrPSc in the 6 sCJD Groups

No. of Cases sCJD Group Upper Glycoform Lower Glycoform Unglycosylated

186 MM1, MV1a 24.1 6 4A 45 6 3B 30.9 6 4C

3 VV1 21.4 6 6D 44 6 5 34.6 6 3E

6 MM2-C 33.3 6 3F 40.8 6 2G 25.9 6 2H

6 MM2-T 25.4 6 4I 41 6 2J 33.6 6 4K

23 MV2 28.3 6 4L 40.8 6 3M 30.9 6 4N

43 VV2 32.7 6 3O 41.3 6 3P 26 6 3Q

aBecause the MM1 and MV1 subjects showed a virtually identical phenotype and glycoform ratio of protease-resistant prion protein (PrPSc),they were combined.

A vs F, A vs L, A vs O, B vs G, B vs J, B vs M, B vs P, C vs Q, L vs O, N vs Q, p , 0.001; C vs H, F vs I, H vs K, H vs N, I vs O, Kvs Q, p , 0.01; D vs F, E vs H, E vs Q, F vs L, p , 0.05 (unpaired two-tailed t test). Data are expressed as mean 6 SD values. Only samplesfrom the cerebral cortex were used.

sCJD 5 sporadic Creutzfeldt-Jakob disease; MM2-C 5 MM genotype type 2 (PrPSc)-cortical; MM2-T 5 MM genotype type 2 (PrPSc)-thalamic.

Fig. Lesion profiles for the different sporadic Creutzfeldt-Jakob disease (sCJD) groups classified according the codon 129 genotypeand the protease-resistant prion protein (PrPSc) type. Because the MM2 subjects showed two distinct profiles, this group has beendivided in two subgroups (cortical and thalamic). MM2 5 MM genotype and type 2 PrPSc. The following gray matter regionswere analyzed: frontal (FC), temporal (TC), parietal (PC), and occipital (OC) neocortices, hippocampus (HI) (CA 1 region), para-subiculum and entorhinal cortex (EC), neostriatum (ST) (nuclei caudatus and putamen), thalamus (TH) (mediodorsal nucleus),substantia nigra (SN), midbrain periventricular gray (PG), locus ceruleus (LC), medulla (ME) (periventricular gray and inferiorolive), and cerebellum (CE). Spongiosis was scored on a 0 to 4 scale (not detectable, mild, moderate, severe, and status spongiosus),astrogliosis and neuronal loss on a 0 to 3 scale (not detectable, mild, moderate, and severe). Lesion profiles were obtained by aver-aging the three scores for each brain region examined. Data are expressed as mean 6 SD values.


ebellum (see Table 3). They also showed less severepathology in the cerebellum compared with the VV2subjects with similar disease duration (see Fig). In ad-dition, a coarse staining was seen in a subset of subjectsin the cerebral cortex (see Table 3). Finally, the lami-nar staining in the cerebral cortex was less consistentlydetected in the MV2 than in the VV2 subjects (seeTable 3).

Clinical FindingsAGE AT ONSET AND DURATION OF SYMPTOMS. Subjectswith either VV2 or MV2 had a statistically significantyounger age at onset than those MM1 (Table 4). In asimilar manner, the VV1 and, to a lesser extent, theMM2-thalamic subjects showed a younger age at onsetthan the other groups.

Subjects MM1 showed a statistically significantshorter duration of symptoms than all the othergroups. In addition, subjects VV2 had a statisticallysignificant shorter duration than MV2, VV1, MMZ-cortical, or MM2-thalamic subjects.

CLINICAL SIGNS AT ONSET. Although there was overlapof clinical features, presenting signs differed among thesCJD groups (Table 5). Cognitive impairment was in-variably present in both VV1 and MM2-cortical sub-jects, but it was absent in most VV2 patients. In con-

trast, ataxia was very common in the VV2 and MV2subjects, but completely lacking in the VV1 andMM2-cortical groups. Visual signs, myoclonus andother dyskinesias were only detected in MM1 or MV1patients. In a similar manner, unilateral signs at onsetwere almost exclusively a feature of the MM1 andMV1 subjects.

CLINICAL SIGNS DURING EVOLUTION. Dementia char-acterized all subjects with the exception of a relativelysmall group of MM1 and MV1 patients who abruptlylapsed into a stupor or coma after showing neurologicalsigns without dementia at onset (Table 6). Ataxia re-mained significantly higher in the VV2 and MV2 sub-jects than in most of the other groups, whereas visualsigns, with the exception of hallucinations, were onlyseen in the MM1 or MV1 groups. Myoclonus was avirtually invariable feature of subjects MM1 or MV1,whereas it was lacking in a significant proportion ofsubjects from the other groups. Furthermore, the meantime of appearance of myoclonus was earlier in theMM1 or MV1 subjects. Finally, progressive insomnia,often accompanied by psychomotor agitation and vi-sual hallucinations, more consistently occurred in theMM2-thalamic phenotype.

Table 3. Patterns of PrPSc Deposition (in %)

sCJD Group(No. of Cases)

MM1(111)

MV1(5)

VV1(3)

MM2-C(5)

MM2-T(6)

MV2(19)

VV2(30)

Cerebellar or cortical synaptic 100 100 100 0 33.3 100 100Cortical perivacuolar 33.3 20 0 100 16.7 21.1 0Cerebellar plaque-like deposits 0 0 0 0 0 100 100Cerebellar kuru plaquesa 0 0 0 0 0 100 0Laminar cortical patternc 0 0 0 0 0 68.4b 90b

aPrP-positive amyloid (visible on hematoxylin and eosin staining) unicentric plaques.bBecomes 100% in subjects with a 4- to 10-month duration of symptoms.cIn the deep cortex (layers 4–6).

PrPSc 5 protease-resistant prion protein; sCJD 5 sporadic Creutzfeldt-Jakob disease; MM2-C 5 MM genotype type 2 (PrPSc)-cortical;MM2-T 5 MM genotype type 2 (PrPSc)-thalamic.

Table 4. Age at Onset and Duration of Symptoms

sCJD Groups(No. of Cases)

MM1(203)

MV1(8)

VV1(3)

MM2-C(6)

MM2-T(6)

MV2(27)

VV2(47)

Age at onseta (yr) 65.5 (42–91)c 62.1 (51–72) 39.3 (24–49) 64.3 (49–77) 52.3 (36–71) 59.4 (40–81) 61.3 (41–80)Durationb (mo) 3.9d (1–18) 4.9 (2.5–9) 15.3 (14–16) 15.7 (9–36) 15.6 (8–24) 17.1 (5–72) 6.5 (3–18)

aMM1 vs MV2, p , 0.01; MM1 vs VV2, p , 0.05 (unpaired, two-tailed t test).bMM1 vs VV1, MM1 vs MM2-C, MM1 vs MM2-T, MM1 vs MV2, MM1 vs VV2, VV2 vs MM2-T, VV2 vs MV2, p , 0.001 VV2 vs VV1p , 0.01 (Mann–Whitney test).cRanges are in parentheses.d88% of cases had a duration of symptoms #6 months.



ELECTROENCEPHALOGRAPHIC FINDINGS. The typicalelectroencephalogram (EEG) with periodic or pseudo-periodic sharp-waves complexes (PSWCs) was stronglyassociated to the MM1 and MV1 subjects (Table 7).In addition, the mean time of appearance of PSWCswas much earlier in the MM1 and MV1 subjects.

DiscussionThe definition of the full spectrum of sCJD variants isimportant for the epidemiological surveillance of the

disease that is currently under way in many coun-tries.36 This study provides the first comprehensiveanalysis of molecular and clinicopathological features ina large series of sCJD patients (Table 8).

The MM1 and MV1 subjects constitute about 70%of our sCJD population, and include cases previouslyclassified as typical CJD of the myoclonic type or asHeidenhain variant.7,11 The typical CJD triad of de-mentia, myoclonus, and PSWCs on EEG is a commonand early feature. In addition, visual signs may precede

Table 5. Symptoms and Signs at Onset (in %)


MM1(199)

MV1(8)

VV1(3)

MM2-C(6)

MM2-T(6)

MV2(27)

VV2(45)

Cognitivea 70 50 100 100 67 74 27Aphasia 23 25 33 33 0 11 0Visualb 26 12 0 0 0 0 0Oculomotor 6 12 0 0 17 19 32Gait or limb ataxia 33 75 0 0 67 81 100Dysarthria 5 12 0 0 33 11 13Myoclonus 18 12 0 0 0 0 0Other dyskinesias 4 0 0 0 0 0 0Pyramidal 6 0 0 0 0 0 0Sensory 7 25 0 0 0 7 15“Psychiatric”c 28 12 0 0 50 34 19Insomnia 8 0 0 0 17 15 9Unilateral 25 25 0 0 0 7 4

aOne or more of memory loss, confusion and/or disorientation, intellectual decline.bOne or more of visual loss, visual field defect, visual distortion, abnormal color vision, cortical blindness.cOne or more of depression or anxiety of recent onset requiring psychiatric evaluation, delusions, hallucinations, panic attacks, psychosis.


Table 6. Symptoms and Signs throughout the Entire Course of the Illness (in %)


MM1(203)

MV1(8)

VV1(3)

MM2-C(6)

MM2-T(6)

MV2(27)

VV2(47)

Cognitivea 94b 75b 100 100 100 100 100Aphasia 36 25 100 83 0 37 0Apraxia 10 0 67 33 0 26 0Visualc 42 12 0 0 0 0 0Oculomotor 8 12 33 0 33 19 32Limb or gait ataxia 52 87 33 17 100 100 100Dysarthria 7 37 0 0 67 26 48Myoclonus (mo) 97 (1.8) 100 (2) 67 (7.5) 67 (10.5) 50 (9) 77 (9) 66 (4.2)Seizures 19 12 0 33 0 11 2Other dyskinesias 18 12 0 17 17 22 20Parkinsonism 7 0 33 33 17 22 6Pyramidald 60 62 67 83 50 81 50Sensory 7 25 0 0 0 7 15“Psychiatric”e 34 12 0 0 67 44 21Insomnia 8 0 0 0 67 15 15

Mean time of appearance of myoclonus (in months after onset) is in parentheses.aMemory loss associated to one or more of confusion, disorientation, intellectual decline, behavioral abnormalities.bThe remaining subjects lapsed into a coma without showing cognitive dysfunction.c and eAs in Table 5.dRigidity with no other specifications has been classified as pyramidal.



severe dementia in about 30% of cases. The his-topathological lesions are distributed in a “classic CJD”pattern (see Fig), although their severity varies, accord-ing to the duration of symptoms.37 One-third of casesshow large confluent vacuoles and a coarse pattern ofPrP staining in the cerebral cortex, in addition to theother phenotypic features.

The VV2 combination represents 16% of subjectsand includes patients previously classified in the ataxic

variant.9,11 Ataxia at onset, isolated or associated withmild cognitive impairment is a consistent feature ofthis phenotype. In contrast to the MM1 and MV1groups, the VV2 subjects do not show PSWCs onEEG in most cases, and about a third of them lackprominent myoclonus. Pathologically, the lesion pro-file, the laminar cortical distribution of spongiform de-generation, and the pattern of PrP deposition distin-guish this variant from the typical phenotype.

Table 7. Electroencephalographic Findings (in %)

sCJD Groups(No. of Cases)

MM1(175)

MV1(7)

VV1(3)

MM2-C(6)

MM2-T(6)

MV2(26)

VV2(42)

Typical 80 71.4 0 0 0 7.7 7.1PSWCsa (2) (1.9) (8) (8)Paroxysmal 9.7 14.3 0 16.6 0 19.2 2.4Dischargesb (1.8) (2) (10) (14) (6)Slowing only 10.3 (1.6) 14.3 (2.5) 100 (8) 83.4 (9.5) 100 (12) 73.1 (9.5) 90.5 (4.1)

The mean time in months of evolution of symptoms at which the electroencephalographic pattern was recorded is shown in parentheses.aPeriodic sharp-waves complexes.bParoxysmal discharges without periodism.


Table 8. Molecular and Phenotypic Features of the Sporadic Creutzfeldt-Jakob Disease (sCJD) Variants

sCJD VariantPreviousClassification

% ofCases

Duration(mo) Clinical Features Neuropathological Features

MM1 or MV1 Myoclonic, Heiden-hain variants

70 3.9 Rapidly progressive dementia, earlyand prominent myoclonus, typicalEEG; visual impairment or unilat-eral signs at onset in 40% of cases

“Classic CJD” distribution of pathology;often prominent involvement of occipi-tal cortex; “synaptic type” PrP staining;in addition, one-third of cases showsconfluent vacuoles and perivacuolar PrPstaining

VV2 Ataxic variant 16 6.5 Ataxia at onset, late dementia, notypical EEG in most cases

Prominent involvement of subcortical, in-cluding brain stem nuclei; in neocortex,spongiosis is often limited to deep lay-ers; PrP staining shows plaque-like, focaldeposits, as well as prominent perineu-ronal staining

MV2 Kuru-plaques variant 9 17.1 Ataxia in addition to progressivedementia, no typical EEG, longduration (.2 yr) in some cases

Similar to VV2 but with presence ofamyloid-kuru plaques in the cerebellum,and more consistent plaque-like, focalPrP deposits

MM2-thalamic Thalamic variant 2 15.6 Insomnia and psychomotor hyperac-tivity in most cases, in addition toataxia and cognitive impairment,no typical EEG

Prominent atrophy of the thalamus andinferior olive (no spongiosis) with littlepathology in other areas; spongiosis maybe absent or focal, and PrPSc is detectedin lower amount than in the othervariants

MM2-cortical Not established 2 15.7 Progressive dementia, no typicalEEG

Large confluent vacuoles with perivacuolarPrP staining in all cortical layers; cere-bellum is relatively spared

VV1 Not established 1 15.3 Progressive dementia, no typicalEEG

Severe pathology in the cerebral cortex andstriatum with sparing of brain stem nu-clei and cerebellum; no large confluentvacuoles, and very faint synaptic PrPstaining

PrP 5 prion protein; PrPSc 5 protease-resistant PrP.


The third most common phenotype (;9% of cases)is the kuru-plaque variant, which is linked to MV atcodon 129 and PrPSc type 2.10,22 Despite its similari-ties with the VV2 phenotype, this variant is character-ized by a longer mean duration of symptoms, a higherfrequency of cognitive impairment at onset, and, mostdistinctively, the presence of kuru-type amyloidplaques.

The other sCJD variants are rarer and represent 5%of cases. The MM2-thalamic phenotype is indistin-guishable from that of fatal familial insomnia and othercases previously classified as thalamic form of CJD orpreferential thalamic degeneration.8,35,38 The associa-tion of thalamic and olivary atrophy, the relative spar-ing of basal ganglia and cerebellum, and the inconsis-tency of spongiform degeneration, which is limited toscattered foci in the cerebral cortex, make this variantunique. Progressive insomnia and psychomotor agita-tion at night, and absence of PSWCs on EEG are typ-ical clinical features.

In the MM2-cortical phenotype, dementia is themain sign, and visual or cerebellar signs, and PSWCson EEG are typically absent. The most distinctivepathological features are the type of spongiform degen-eration, which is characterized by large, confluent vacu-oles, and the pattern of PrP staining, which is coarse.

The VV1 subjects, like the MM2-cortical group,show a clinical phenotype dominated by cortical signsand progressive dementia, with neither typical EEGsnor early cerebellar signs. However, pathological fea-tures such as the type of spongiform changes, and thepattern of PrP deposition, clearly distinguish the twogroups.

Some subjects (9 MM1, 1 MV1, 1 VV2, and 1MV2) showed severe pathology including a significantinvolvement of the white matter, which would justifytheir classification with the panencephalopathic variantof CJD.39 As a common feature, they all had a longerduration of symptoms (12 6 2, 9, 18, and 72 months,respectively) than most cases of the group to whichthey belong. Based on these observations, we suggestthat the panencephalopathic variant of CJD is not adistinct entity, but rather an end-stage conditionshown by individual cases with an unusually prolongedcourse. In a similar manner, our data do not supportthe existence of a sCJD variant that fits the definitionof an amyotrophic form of CJD.40,41

The results of the present study invites changes inour current view and diagnostic approaches to CJD. Itis increasingly evident that, although the “classic”MM1 or MV1 phenotype (rapidly progressive myo-clonic dementia associated with PSWCs on EEG) isthe most common expression of sCJD, there are fiveother sCJD variants that display less typical features. Itis noteworthy that many of these atypical symptomsand signs, such as the young age at onset, the pro-

longed disease course, and the absence of periodiccomplexes on the EEG are part of the clinical pheno-type of nvCJD,4 and consistently considered amongthe features that separate nvCJD and sCJD as distinctclinical entities. All our VV1 subjects, 50% of theMM2-thalamic cases, and 33% of the MV2 subjectshad the onset of symptoms in their 40s or earlier. Inaddition, all these subjects had a relatively prolongedcourse of more than 1 year, and almost all of themlacked PSWCs on EEG. Our report emphasizes theneed for more awareness of these atypical sCJD vari-ants. Continued attention to clinically atypical cases isalso required to monitor the incidence of these sCJDvariants, and may lead to the discovery of additionalphenotypes. To reach these goals, neuropathologicalexamination, including the search for PrPSc by immu-nohistochemical and western blot analysis, should beincreasingly applied to atypical progressive neurologicaldisorders.

Clinical data are more informative for the MM1 orMV1 subjects. Some clinical signs, such as visual fielddefects, visual distortion, or reduced visual acuity ofcortical origin, myoclonus, or other dyskinesias, appearto be specific for this phenotype when observed withinthe first 2 months of symptoms. Unilateral signs at on-set are also an almost exclusive feature of this variant.Finally, PSWCs on EEG are recorded within the first 4months of symptoms only in the MM1 and MV1 sub-jects. The early recognition of these clinical signs, com-bined with PRNP genotyping, detection of the 14-3-3protein in cerebrospinal fluid,42 and, possibly, diffusionmagnetic resonance imaging,43 should allow the clini-cal identification of the MM1 and MV1 affected sub-jects with high accuracy.

The present results extend our earlier observationson the molecular basis of phenotypic variability inCJD.22 The conclusion that there are physicochemicalproperties of PrPSc that influence the phenotypic ex-pression of sCJD independently from the primary PrPsequence was based on the observation of two distinctphenotypes in PRNP syngenic MM subjects that cor-related with distinct types of PrPSc. In support of thisdata, we have now found that the codon 129 MV andVV genotypes can be associated with either type 1 ortype 2 PrPSc, and that each combination correlateswith distinct phenotypes. In addition, we have identi-fied a third phenotype in the MM population, a “tha-lamic” variant. Although the PrPSc associated with thisphenotype shares the type 2 pattern of electrophoreticmobility with other sCJD variants, it can be distin-guished from those by its slightly different glycoformratio.

Our findings, combined with those obtained by re-cent transmission studies, support that at least threedistinct strains of the pathogenic agent, in addition tothe BSE strain, are found in the human population.


Because striking phenotypic similarities exist betweenthe MM1 and MV1 subjects and between the MV2and VV2 patients, despite the different codon 129 ge-notype, whereas two phenotypes are linked to distinctPrPSc types in MV syngenic subjects, it seems that theMM1-MV1 and the MV2-VV2 variants behave liketwo distinct prion strains. Strong support for this hy-pothesis has recently been provided by a transmissionstudy.44 Evidence for an additional human prion straincomes from transmission of fatal familial insomnia,which demonstrated that the transmissible agent linkedto this familial prion disease has biological propertiesdistinct from that associated with the MM1 pheno-type.22 Thus, a third CJD strain is likely to be linkedto the MM2-thalamic phenotype. Whether the VV1and MM2-cortical phenotypes are associated with ad-ditional strains or are determined by other host geneticfactors remains to be determined.

In conclusion, our study of a large number of caseshas led to the identification of six distinct clinicopath-ological variants of sCJD, which appear to be largelyspecified by the genotype at codon 129 of PRNP, andthe physicochemical properties of PrPSc. These variantsmay originate either from stochastic events or prion in-fection, in combination with host genetic factors.Whichever the case, our findings significantly expandthe foundation for future epidemiological studies onthe pathogenesis of sCJD.

Supported by NIH grants AG08155, AG08992, AG10133, theCDC grant CCU 515004, the Britton Fund, the Ministere dela Sante PHRC AOM 96117, and the Bundesministerium furGesundheit.

We are indebted to the many physicians who provided clinical in-formation or pathological material regarding the patients studied, toDiane Kofskey for technical assistance, and to Dr Gianluigi Zanussofor his help in collecting tissue. Some human brain tissue was pro-vided by the Joseph and Kathleen Bryan Brain Bank at Duke Uni-versity Medical Center, the ADRC Brain Bank at Columbia Uni-versity, and the Harvard Brain Tissue Resource Center (HarvardMedical School/McLean Hospital, Belmont, MA). Part of this studywas made within the EU Concerted Action on Human Transmis-sible Spongiform Encephalopathies.

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Classification of sporadic Creutzfeldt-Jakob disease based on molecular and phenotypic analysis of 300 subjects