Transcript Spongiform-Encephalopathies

Spongiform Encephalopathies
Dr. Cathal Collins
14/02/05
Introduction
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Prion disease
Neurodegenerative
Long incubation period
Progresses inexorably
5 human prion diseases:
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Kuru
Creutzfeldt-Jokob disease (CJD)
New variant CJD
Gerstmann-Straussler-Scheinker syndrome
Fatal familial insomnia
Neuropathology
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Neuronal loss
Proliferation of glial cells
Absence of an inflammatory response
Presence of small vacuoles which
produces a spongiform appearance
Animal prion diseases
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Scrapie: sheep, goats; first described 1738
Transmissible Mink Encephalopathy: minks;
1964
Chronic Wasting Disease: mule, deer, elk;
1980
Bovine Spongiform Encephalopathy: cattle;
1986
Feline Spongiform Encephalopathy: cats;
1990
BSE History in UK
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1985: first cases of BSE
1988:
June
BSE made notifiable
July
Ruminant feed banned
August
Compulsory slaughter
and destruction of
suspect cattle
1989
February Southwood report
November Ban of sale of bovine
offal for human
consumption
BSE History in UK
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1990
1992:
1996:
November Bovine offal
feed ban for all
animals and birds
Peak incidence of BSE
First cases of nvCJD
Further restriction of bovine
products from food and food
chains
Biology of Prions
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Dr. Stanley Prusiner: coined the term “prion” in 1982:
proteinacious infectious particle
Small infectious pathogen containing protein and
lacking nucleic acid
One characteristic feature is their resistance to a
number of normal decontaminating procedures
Resistant to:
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Aldehydes e.g formaldehydes
Nucleases
Heat (80C)
UV and ionising radiation
Non-ionic detergents
Biology of Prions
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Inacticated by:
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Prolonged autoclaving (at 121C and 15psi for 4.5h)
Immersion in 1M NaOH (for 30 min, repeat 3 times)
Immersion in strong organic solvents
Inadequate autoclaving can establish
heat resistant subpopulations
Stainless steel instruments may also
retain infectivity even after treatment
with 10% formaldehyde
Prion Protein (PrP)
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The gene (PRPN) is located on the short arm
of chromosome 20
Encodes a protein (PrPc) found in normal
brain (alpha helical); normal function
unknown
PrPsc (PrP in scrapie infected anmals) is a
conformational isomer of PrPc (B-pleated
sheet)
PrPsc is resistant to digestion with proteases
and has a tendency to polymerise into
scrapie-associated fibrils or prion rods
Biosynthesis of PrPc
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Key step is modification of amino and carboxy
terminals with the addition of a
phosphatidylinositol glycolipid which serves to
anchor the protein to the cell surface
PrPc is found attached to plasma membranes
of neurons and may be concentrated at
synaptic membranes
PrPc has transmembranous domains
Degraded after endocytosis in acidic vesicles
PrPsc
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Accumulates within cells; does not normally
appear on the cell surface
Found predominantly in cytoplasmic vacuoles
and secondary lysosomes
Studies with mice either devoid of PrPc or
with abnormal isoforms indicate that host
PrPc must be present for the development of
prion disease
Prion diseases result from accumulation of
abnormal isoforms of the PrP which is
dependent upon conversion of PrPc to PrPsc
PrPsc
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How the first molecule of PrPsc appears in
the host remains a mystery
Exogenous source in sporadic and iatrogenic
CJD
Mutation in PRNP gene in familial forms
The initial appearance (?de novo) probably
triggers the replication of PrPsc; PrPc acts as
a nidus for the formation of PrPsc on
challenge
PrPsc
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Prior to transport to the nervous system,
follicular dendritic cells within germinal
centres of lymhoid tissue appear to act as a
reservoir for the protein
Two reports suggest that complement plays a
role in early pathogenesis ( C3, C1q, Bf/C2, or
complement receptors)
Transport of PrPsc to the nervous system
occurs via axons
Neurotoxicity of prion protein
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PrPsc causes apoptosis and cell death
Misfolded PrP is transported to the
cytosol for degradation- even small
amounts of this protein in the cytosol
are highly neurotoxic
Accumulation of this protein may be an
important step in prion disease
pathogenesis
Genetics
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PRNP encodes PrP and is located on the short
arm of chromosome 20
A strong link has been established between
mutations in the PRNP gene and forms of
prion disease with a familial predisposition
(fCJD, GSS, FFI)
More than 50 different mutations have been
identified
A single mutation may produce different
clinical phenotypes in different individuals or
families
Genetics
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The phenotype of a particular mutation may
be influenced by the nature of the amino
acids present at codon 129
Normal individuals have either valine or
methionine at this site
PRNP is an autosomal dominant gene; can be
homozygous or heterozygous
D178N mutation (asparagine for aspartic acid
in codon 178): Homozygous for valine at
codon 129 appear to develop CJD; those
homozygous for methionine tend to have FFI
Genetics: Codon 129
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Molecular classification scheme for sporadic
CJD based upon codon 129 polymorphism
and characterisation of the properties of
PrPsc
A pattern of type 1 PrPsc plus at least 1
methionine at codon 129 was demonstrated
in 70%
Type 2 PrPsc plus codon 129 homozygous or
heterozygous for valine was present in 25%
and associated with ataxia
Genetics: CJD
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Familial CJD: most common mutation is a
substitution of lysine for glutamine in codon
200; phenotype may depend on codon 129
Sporadic CJD and iatrogenic CJD are not
associated with PRNP gene mutations;
however in these forms and nvCJD,
phenotyping at codon 129 appears to affect
susceptibility and perhaps expression of the
clinical illness
Genetics: GSS and FFI
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GSS
- P102L mutation is the most common
PRNP
- large degree of phenotypic
heterogeneity
- polymorphism at codon 129 may play a
modulating role
FFI
-D178N mutation predominant in those
homozygous for methionine at codon 129
Kuru
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First transmissible
neurodegenerative
disease to be
identified and well
studied
Has served as the
prototype of human
prion diseases
Kuru- Epidemiology
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Was endemic in Papua New Guinea among
the Fore tribes
Felt to be transmitted from person to person
by ritual cannibalism
Still remains uncertain as to whether the
brain was actually eaten, but it was handled
after death, particularly by females and
children
No cases observed since these practices
discontinued
Primary cause of death in the tribes in 1960s
Kuru- Clinical Features
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Ambulatory phase: tremors (kuru=shivering),
ataxia and postural instability
Sedentary stage: loss of ambulation resulting
from increased tremors and ataxia;
involuntary movements
Late stage: dementia, indifference
Terminal stage: frontal release signs,
cerebellar type dysarthria and inability to get
out of bed
Death typically due to pneumonia occurring
within 9-24 months form onset of disease
Kuru- Diagnosis&Pathology
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CSF unremarkable, EEG not
characteristic
Pathological hallmark is PrPsc-reactive
plaques occurring with the greatest
frequency in the cerebellum; neuronal
loss and hypertrophy of astrocytes is
also observed
Creutzfeld-Jakob Disease
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Most frequent of the human prion
diseases
Still very rare
Sporadic (sCJD), familial (fCJD),
iatrogenic (iCJD) and new variant
(nvCJD)
CJD- Epidemiology
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Approx 1 case per 1 million population/year
World-wide distribution
Mean age of onset is 57-62
Patients with nvCJD and iCJD tend to be
much younger
No gender predilection
Incidence increased 30-100 fold in certain
areas of North Africa, Israel and Slovakia, due
primarily to clusters of fCJD
Vast majoriy sporadic (85-95%), 5-15% fCJD,
<5% iCJD
Iatrogenic CJD
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Following administration of cadaveric
human pituitary hormones, dural graft
transplants, use of dural mater in
radiographic embolisation procedures, corneal
transplants, liver transplants, and the use of
contaminated neurosurgical instruments or
stereotactic depth electrodes
Hx of preceding infusion does not increase
risk of developing CJD (epidemiology
studies); however low levels of infectivity in in
vitro studies
CJD- Clinical Features
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Rapidly progressive mental deterioration and
myoclonus are two cardinal manifestations of
sCJD
Number of variants or subtypes of disease
based based upon area of involvement of the
brain
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Visual
Cerebellar
Thalamic
Striatal
Variants of sCJD also classified based on
genotype of PRNP and the molecular
properties of the pathological PrPsc
CJD- Clinical Features
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Mental deterioration may manifest as
dementia, behavioural abnormalities and
deficits involving higher cortical function
Concentration, memory and judgement
difficulties are frequent early signs
Mood changes such as apathy and depression
are common
Dementia becomes dominant and can
advance rapidly
Death usually occurs within one year
CJD- Clinical Features
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Myoclonus, especially provoked by startle, is
present in more than 90%
sCJD should always be considered in a
patient with a combination of a rapidly
progressive dementia and myoclonus
Extrapyramidal signs such as hypokinesia and
cerebellar manifestations including nystagmus
and ataxia occur in 2/3
Corticospinal tract involvement in 40-80%
Sensory signs and symptoms are common in
nvCJD; otherwise extremely atypical
Subtypes of sCJD
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Clinical phenotypes of sCJD associated with
molecular subtypes determined by the PRNP
gene codon 129 genotype and the pathologic
prion protein (PrPsc) type
PRNP genotype homozygous or heterozygous
for methionine (M) or valine (V) at codon 129
The PrPsc type is determined by Western blot
analysis amd classified in the Parchi/Gambetti
nomenclature as type 1 or type 2
Alternate Collinge nomenclature distinguishes
4 PrPsc subtypes: types 1 and 2 correspond
with P&G PrPsc 1; 3 and 4 with P&G PrPsc 2
Subtypes of sCJD
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6 clinical phenotypes of sCJD
MM1 and MV1 (myoclonic, Heidenhain
variant) account for about 70% of cases and
correlate with the “classic CJD” phenotype
VV2 (ataxic variant) accounts for 16%
MV2 (Kuru plaque variant): 9%
MM2 thalamic, MM2 cortical and VV1 account
for the rest
CJD- Diagnosis
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Clinical and laboratory features generally are
sufficient for a ‘probable’ diagnosis of sCJD
WHO criteria for ‘probable’ diagnosis:
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Progressive dementia
>/=2 of 4 of: myoclonus; visual or cerebellar
disturbance; pyramidal/extrapyramidal
dysfunction; akinetic mutism
A typical EEG during an illness of any duration
and/or positive 14-3-3 CSF assay with a clinical
duration to death in less than 2 years
Routine investigations should not suggest an
alternative diagnosis
CJD-Diagnosis
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A definitive diagnosis requires these features
in combination with one or more of the
following:
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Loss of neurons, gliosis, spongiform degeneration, or
plaqes postive for PrPsc on histopathlogy of brain
tissue
Positive PrPsc staining following pretreatment of
brain tissue to destroy PrPc reactivity
Positive histoblotting of brain tissue extracts for
PrPsc after treatment to destroy PrPc reactivity
Transmission of characteristc neurodegenerative
disease to experimental animals
Demonstration of PRNP gene mutations
CJD- Diagnosis
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Neuroimaging: diffusion weighted MRI- can
detect abnormalities as early as 3 weeks of
symptom duration, CT generally normal
EEG: aids diagnosis: characteristic pattern of
periodic synchronous bi or triphasic sharp
wave complexes (PSWCs)
Protein markers: 14-3-3 protein in CSFespecially in those with classical subtypes of
sCJD
Pathological studies of brain material to
detect protease resistant PrPsc remains gold
standard
New Variant CJD
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Initial reports of nvCJD
in 1996 quickly focused
intense interest on the
human prion diseases
Linked with bovine
spongiform
encephalopathy
Unique epidemiological
features of this illness
led to early recognition
that this was indeed a
”new variant”
nvCJD- Epidemiology
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First report of a case of nvCJD in a 16 year
old from the UK appeared in 1995 was quickly
followed in 1996 by 22 other cases
All bar one of the initial cases were from the
UK
January 2004- 155 cases world-wide
145 from UK, 6 from France, 1 each from
Ireland, Italy, Canada and the US
All except the italian had resided in countries
with known BSE
nvCJD V sCJD
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nvCJD is distinguished from sCJD by
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A considerably younger age of onset (mean age of
onset 29 versus 65)
Less rapid progression of disease (duration 14
months versus 4-5)
Differences in clinical presentation (sensory and
psychiatric symptoms prominent in nvCJD)
Type 2 (P&G)/ type 4 (Collinge) PrPsc in nvCJD
Differences in neuropathology
nvCJD- Clinical features
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63/100 of the 1st cases presented initially with
psychiatric symptoms
Neurological symptoms preceded psychiatric
in 15
Both were present in 22
Psychiatric symptoms include depression,
apathy, anxiety, psychosis and intermittent
delusions
Sensory abnoramalities include dysaesthesias
and paraesthesia of the face, hands, feet,
legs or even hemibody
nvCJD- Clinical features
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Once neurological symptoms, typically ataxia,
becomes evident, progression is more rapid
Cognitive impairment, involuntary
movements, immobility, unresponsiveness,
and mutism are common signs as the disease
progresses
Paresis of upward gaze may be present
(uncommon in other forms of CJD)
nvCJD- Diagnosis
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CSF studies rarely helpful: 14-3-3 is not a
sensitive marker
Combination of 14-3-3 and tau protein in CSF
may be useful
MRI better than CT: MRI may show signal
hyperintensity in the pulvinar (pulvinar sign)
or in both pulvinar and dorsomedial thalamus
(hockey stick sign)
EEG: abnormal in 70% but only slow wave
pattern
nvCJD- Diagnosis
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PRNP gene mutations are not present in
nvCJD, but all patients with clinically
expressed nvCJD have been homozygous for
methionine at codon 129
Type 2 PrPsc (P&G nomenclature) or type 4
PrPsc in the Collinge nomenclature has been
found in patients with nvCJD (not
characteristic of other human prion diseases)
nvCJD- Neuropathology
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A number of neuropathological feature
distinguish nvCJD from sCJD:
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Presence of plaques, which stain intensely for
PrPsc, distributed throughout the cerebrum and
cerebellum and to a lesser extent the basal
ganglia and thalamus
The plaques have an eosinophilic centre and pale
periphery with surrounding spongiform changes
Cases of kuru and GSS have similar but not
identical plaques
The cerebellum is characteristically involved in
nvCJD
nvCJD has distinct type 4 PrPsc
nvCJD- Links
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2 cases of possible transfusion
transmisssion of nvCJD have been
reported
There is increasing evidence supporting
the possibility that nvCJD represents
bovine-to-human transmission of BSE
nvCJD and BSE
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The appearance of nvCJD followed an
epidemic of BSE in the UK
The removal of organic solvents, which
inactivate PrPsc, from the rendering process
for bovine offal and the subsequent use of
the offal as a component of feed for cattle
has been suggested as a mechanism for
amplifying the epidemic in animals
Approx 50,000 infected cattle are estimated
to have entered the food chain
nvCJD and BSE
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The prohibition of ruminant-derived proteins
in feeds for all animals and poultry in
november 1990 and the banning of
consumption of animals over the age of 30
months in March 1996 has led to a dramatic
decline in cases of BSE
Evidence in the favour of the association
between nvCJD and BSE includes the type 4
pattern of PrPsc which has not been seen in
other prion diseases
nvCJD and BSE
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Despite the apparent link between nvCJD and
BSE, the number of cases of nvCJD has
remained small. Possible reasons include:
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Low levels of PrPsc in milk and meat
Inefficiency of oral route of infection
Restriction of spread based upon a species barrier
Low incidence of host genetic factors such as the
frequency of homozygosity at codon 129
Gerstmann-StrausslerScheinker Syndrome
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A rare human prion disease
1-10 cases per 100 million population/year
Autosomal dominant pattern with virtual
complete penetrance
Hallmark: progressive cerebellar degeneration
accompanied by different degrees of
dementia in patients entering mid-life (mean
43-48)
Course of illness advances for 5 years before
culminating in death
Myoclonus is typically absent
GSS
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Phenotypic variability due to differences in
underlying PRNP mutation or in the
polymorphism in codon 129
Lab or imaging studies not useful
Demonstration of PRNP mutation useful
means for diagnosis
Neuropathological features consistent with
other forms of prion disease: however kurulike plaques especially in the cerebellum are
common findings; also neurofibrillary tangles
and neuropil threads identical to those seen
in Alzheimers
Fatal Familial Insomnia
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Rapidly fatal with a mean duration of 13
months; midlife (35-61 years)
Develop progressive insomnia with loss of
normal circadian sleep-activity pattern
Impaired concentration and memory,
confusion, inattention and behavioural
changes occur but overt dementia is rare
Myoclonus, ataxia and spasticity occur with
disease progression
FFI
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Only prion disease to produce dysautonomia
(increased T, BP, HR) and endocrine
disturbances (ACTH, cortisol, GH, PRL)
Genetic studies are diagnostic procedure of
choice
Most cases associated with D178N PRNP
mutation
Spongiform degeneration rarely detected;
neuronal loss and gliosis is maximal within
the thalamus
Treatment of Prion Diseases
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No effective treatment has been identified for
human prion diseases which are universally
fatal; supportive treatment mainstay
Flupirtine maleate is a centrally acting, nonopioid analgesic that has displayed
cytoprotective activity in vitro in neurons
treated with a prion protein fragment: better
MMSe but survival not enhanced
Chlorpromazine and quinacrine: inhibit PrPsc
formation in vitro: studies needed
Potential targets will include the steps in the
conversion of PrPc to PrPsc
Summary
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Prions: do not have nucleic acid
Conversion of PrPc to PrPsc
Codon 129 in PRNP gene
Neurodegenerative diseases
Long incubation period
Progress inexorably; no treatment
5 types of human prion disease
nvCJD and links to BSE