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A New PRNP Mutation (G131V) Associated With Gerstmann-Sträussler-Scheinker Disease
Peter K. Panegyres, PhD, FRACP;
Kathrine Toufexis, BSc (Hons);
B. A. Kakulas, MD, FRCPA, FRACP;
Larisa Cernevakova, MD;
P. Brown, MD;
B. Ghetti, MD;
P. Piccardo, MD;
S. R. Dlouhy, PhD
Arch Neurol. 2001;58:1899-1902.
ABSTRACT
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Background Gerstmann-Sträussler-Scheinker disease is
a rare form of prion disease.
Objective To determine the prion mutation in a
51-year-old man without a family history of neurologic disease who died
from Gerstmann-Sträussler-Scheinker disease.
Patient and Methods The patient was a 51-year-old man who died
after a 9-year illness characterized by dementia and eventually ataxia.
Neuropathologic studies were performed, the results of which revealed
abundant prion protein–immunopositive amyloid plaques in the
cerebellum without spongiform degeneration.
Results Genetic analysis of the prion protein gene showed a
novel mutation at codon 131 that caused a valine-for-glycine
substitution (G131V) and homozygosity at codon 129 (129M).
Proteinase K–resistant prion protein was detected by Western blot
analysis.
Conclusions This is the first mutation described in the short,
antiparallel ß-sheet domain of the prion protein. This report
highlights the importance of genetic analysis of patients with atypical
dementia even in the absence of a family history.
INTRODUCTION
GERSTMANN-Sträussler-Scheinker disease (GSS) is an autosomal dominant
neurodegenerative disease caused by mutations in the prion protein gene
(PRNP).1 Clinically, it is characterized
by progressive ataxia and dementia; pathologically, it is characterized
by prion protein (PrP) amyloid plaques and neuronal loss.
Mutations in PRNP have been found to be associated with GSS,
Creutzfeldt-Jakob disease (CJD), and fatal familial insomnia. The GSS
phenotype has been associated with point and insertional
mutations.2, 3, 4, 5 Some of these PRNP mutations have
been used to establish genetic linkage between the mutation and the
disease phenotype. Herein, we report a novel PRNP mutation in
a patient with an unusual phenotype.
PATIENT AND METHODS
A white man, born in 1945, resigned in 1987 from his position as a
teacher following complaints from colleagues regarding his inability to
discipline his class. His driving was erratic and he was unable to find
his way on the roads. There was impairment of his short-term memory,
reduced learning capacity, perseverance, and emotional immaturity. His
family reported aloofness, anxiety, and increasing anger. The family,
including the patient's 2 siblings, who are in their 50s, and his
teenage son, has no history of neurologic disease.
In 1987, during a neurologic examination, the man appeared to have no
insight into his condition. He was apraxic and had a tremor of the
limbs and gegenhalten. Visuospatial skills and spatial orientation were
impaired and he was dyscalculic. The deep-tendon reflexes were
pathologically brisk; the cranial nerve examination results and
peripheral motor systems were otherwise normal. There was no ataxia.
A neuropsychological assessment revealed a Mini-Mental State
Examination score of 22/30 and a verbal IQ of 88, a performance IQ of
67, and a full-scale IQ of 78. Results of block design and object
assembly subtests from the Wechsler Intelligence Scale were abnormal.
He was grossly impaired on tests of verbal short-term memory,
reasoning, comprehension of visual information, and visuospatial
organization. The computed tomography and magnetic resonance images
showed cerebral and cerebellar atrophy. Results of examination of the
cerebrospinal fluid were normal, except for a slightly elevated protein
level concentration of 0.046 g/dL (reference range, 0.015-0.045
g/dL). The electroencephalogram did not show periodic sharp
waves.
His dementia progressed and ataxia developed. He eventually required
institutionalization in a locked ward because of uncontrollable
aggressive behavior. He died by choking at the age of 51 years, 9 years
after the onset of symptoms.
RESULTS
NEUROPATHOLOGIC FINDINGS
On autopsy, the brain weighed 1243 g. There was mild cerebral and
cerebellar atrophy. Microscopically, numerous congophilic amyloid
plaques were found in the cerebellum. For immunohistochemical detection
of the PrP deposits, antibodies recognizing the N-terminus (PrP 23-40),
midregion (PrP 95-108, 3F4), and C-terminus (PrP 220-231) of
PrP were used (Figure
1). The PrP immunoreactivity was
intense in the molecular layer of the cerebellum. In addition, PrP
deposition was found in the following brain regions: Ammon horn;
frontal, temporal, and parietal cortices; and corpus striatum and
thalamus. In addition, PrP was not detected in the midbrain, pons,
medulla, and mamillary bodies. There was no spongiform degeneration.
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Figure 1.
Anti–prion protein (PrP) immunohistochemistry. The molecular layer of
the cerebellar cortex shows large PrP deposits (hematoxylin
counterstain, original magnification x400).
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By modified Bielschowsky stain, occasional neurons with neurofibrillary
tangles (NFTs) were seen in the Ammon horn and entorhinal cortex.
However, NFTs were not found in any other area of the central nervous
system.
GENETIC ANALYSIS
DNA was extracted from the cerebellum, and polymerase chain reaction
was used to amplify the open reading frame of the PRNP gene
using the following human PRNP primers (Genbank submission
M13899).6 For forward 5'-3', region 1, position
31 to 51, 21-mer CCG AGG CAG AGC AGT CAT TAT; region 2, position 311 to
329, 19-mer GGC TGG GGT CAA
GGA GCT G; and region 3, position 582 to 603,
22-mer ACT GCG TCA ATA TCA CAA TCA A. For reverse 5'-3',
region 1, position 400 to 417, 18-mer CCC ACC ACT GCC CCA GCT; region
2, position 673 to 693, 21-mer ATA CAC ATC TGC TCA ACG ACG; and region
3, position 945 to 963, 19-mer AGT GCC CAT CAG TGC CAA G.
An automated DNA sequencer (ABI 377; Applied Biosystems, Inc,
Foster City, Calif) was used. The sequencing was performed in a forward
and reverse direction on 3 separate occasions. A G T transversion
mutation at codon 131 was found, resulting in a substitution of valine
(V, GTA) for glycine (G, GGA) at that position (G131V). In
addition, codon 129 was homozygous for methionine (Figure
2). The mutation was confirmed
in subsequent experiments in the laboratories of the American Red
Cross, Rockville, Md, and Indiana University, Indianapolis, and has not
been seen in the DNA from other patients with prion diseases or healthy
controls (N = 50).
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Figure 2. Sequence data of the open reading from the prion protein
(PRNP) gene. The nucleotide number is shown in the upper left
of each row and the normal sequence at the top of each row; slashes
represent homology to the wild-type sequence and the codon number is
under each rectangular shaded box. The sequence of our patient X96/323
is shown under the wild-type sequence. A point mutation at g T is
shown at codon 131 and methionine homozygosity at codon 129. The
controls were run concurrently. D98-414 is a healthy patient; D92-307,
familial Creutzfeldt-Jakob disease with codon 200 mutation; and
D94-483, familial fatal insomnia with codon 178 mutation. Identical
results were obtained on 3 separate runs with sequencing performed in a
forward (F) and reverse direction.
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PrP ANALYSIS
Protein was extracted from the cerebellum and processed as
previously described.7 The presence of protease-resistant
PrP was determined by digestion with proteinase K (PK) and
fractionation in sodium dodecyl sulfate–polyacrylamide gel
electrophoresis. The gels were probed with the monoclonal antibody 3F4
(1:50 000), which recognizes positions 109 to 112 of
human PrP. The immunoblots were visualized using
electrochemiluminescence. Non–PK-treated samples contained PrP species
of
approximately 18, 26 to 27, and 31 to 36 kd. In
addition, PK digestion demonstrated evidence of proteinase-resistant
PrP with bands at approximately 8, 18, 26, and 31 kd (Figure
3).
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Figure 3.
Immunoblot of Creutzfeldt-Jakob disease E200K (A, B) and
Gerstmann-Sträussler-Scheinker disease G131V (C, D) showing the
effect of proteinase K treatment. Brain extracts were untreated (A, C)
or treated with proteinase K (B, D). The position of relative
molecular weight standards corresponding to molecular masses (from top
to bottom) of 30, 20, and 6 kd are shown. Immunoblot probed with
monoclonal antibody 3F4.
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COMMENT
The transmissible spongiform encephalopathies represent a
unique group of neurologic conditions in which genetic disorders can
lead to transmissible neurologic disease. Herein, we describe a de novo
mutation in PRNP associated with a GSS phenotype. In the
proband's family, there was no history of neurologic disorders, and
his 2 siblings, in their 50s, were examined by one of the authors
(P.K.P.) and were found to be free of neurologic signs. They declined
predictive gene testing despite counseling. The absence of a family
history might suggest that this is a new mutation; however, this is
rare for PRNP mutations.
More than 20 mutations in PRNP have been described that cause
CJD, GSS, fatal familial insomnia, and PrP cerebral amyloid angiopathy
with different clinical and neuropathologic phenotypes. Clinically, GSS
is characterized by ataxia, parkinsonian signs, and dementia. In the
proband, ataxia and dementia were the main signs. The most common
mutation associated with GSS is P102L, but other point mutations at
codons 105, 117, 198, 202, 212, and 217 and insert mutations (6 to 9)
between codons 51 and 91 have been described.4 The
disorders caused by these mutations have their onset in the third to
sixth decades of life and usually present with cerebellar ataxia that
evolves to dementia. Our patient had cognitive impairment before the
onset of ataxia, with survival of about 9 years. Cognitive impairment
before the onset of ataxia has also been documented in a family with a
mutation at codon 198.8 Phenotypic heterogeneity has been
previously emphasized in GSS, and it has been recently demonstrated
again in 2 studies of an English and French family with the A117V
mutation and an octapeptide insertional mutation,
respectively.4, 9, 10 The presence of neurologic and
psychiatric symptoms in members of these 2 families further illustrates
the phenotypic variability of these conditions.9, 10
Our patient was homozygous for methionine at codon 129. Homozygosity
for either methionine or valine affects susceptibility to CJD and the
phenotypic expression of mutations.11 For example, in the
case of the D178N mutation, the haplotype 129M-D178N is
associated with fatal familial insomnia and the haplotype
129V-D178N is associated with CJD.12
Prion diseases share a similar pathogenetic mechanism that involves the
conversion of a normal PrP (PrPc) into a pathologic form that is
insoluble in detergents and PK resistant (PrPres). Previous
studies6 have shown that patients with GSS accumulate N- and- C-truncated PrPres fragments of approximately 8 to 15 kd and
variable amounts of higher-molecular-weight isoforms. In addition, in
the GSS variant P102L, PrPres species of approximately 21 to 30 kd,
identical to those described in CJD, are also present when this variant
is associated with severe spongiform degeneration.6, 13 The
pattern of PrPres bands in the proband does not present CJD-like
isoforms (ie, 21- to 30-kd bands). This case is characterized
by PrPres species that are similar to those described in GSS F198S and
Q217R, 2 GSS variants without spongiform degeneration. The mutation
reported herein is the first one to cause an amino acid substitution (G
V) in a short, antiparallel ß-sheet domain comprising residues
128 to 131.8 The impact of such mutation on PrP folding and
processing remains undetermined.14
In the proband, NFTs were observed in the hippocampus and entorhinal
cortex. The NFTs have been previously described in GSS with
mutations F198S and Q217R.15, 16 In these 2 GSS variants,
tau-immunopositive NFTs were widespread in the neocortex and
subcortical nuclei and were associated with neuritic plaques. The
occurrence of different degrees of tau pathologic findings in GSS,
including the G131V variant, requires further investigation to
determine whether hyperphosphorylation of the microtubule-associated
protein tau and the formation of paired helical filaments are secondary
events to the presence of specific conformations of PrP or reflect a
nonspecific phenomenon.
The G131V mutation is another example of the wide spectrum of
phenotypes associated with GSS and PRNP gene mutations and
highlights the importance of the molecular classification of prion
disorders, even in the absence of an identifiable family history. The
diagnostic workup of patients with early-onset dementia and the
suspicion of prion disease necessitates analysis of the PRNP
gene, since neuropathologic features, typical of prion diseases, might
not always be found.17
AUTHOR INFORMATION
Accepted for publication January 17, 2001.
The work was supported by the National Health and Medical Research
Council of Australia, Canberra; Royal Perth Hospital Research
Foundation, Perth; the Medical Research Fund of Western
Australia, Perth; and grant PHS P30 AG 10133 from the US Public Health
Service, Washington, DC (Dr Ghetti).
We thank the staff of the Neuropathology Department, Royal Perth
Hospital, for their help in the production of the manuscript. Rose
Richardson, Albert William, and Yue Feng provided valuable technical
assistance. Bradley S. Glazier helped in the editing process.
From
the Department of Neuropathology, Royal Perth Hospital, Perth, Western
Australia (Drs Panegyres and Kakulas and Ms Toufexis); Jerome H.
Holland Laboratory, American Red Cross, Rockville, Md (Dr Cernevakova);
Laboratory of Central Nervous System Studies, National Institute of
Neurological Disorders and Stroke, National Institutes of Health,
Bethesda, Md (Dr Brown); and Departments of Pathology and Laboratory
Medicine
(Drs Ghetti and Piccardo) and Medical and Molecular
Genetics (Dr Dlouhy), Indiana University School of Medicine,
Indianapolis.
Corresponding author and reprints: Peter K. Panegyres, PhD, Department
of Neuropathology, Royal Perth Hospital, Wellington Street, Perth,
Western Australia 6000 (e-mail: peter.panegyres{at}rph.health.wa.gov.au).
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