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J Neuropathol Exp Neurol. Author manuscript; available in PMC 2011 December 1.
Published in final edited form as:
PMCID: PMC3136530
NIHMSID: NIHMS267298

Pathological Evidence that the T188R Mutation in PRNP Is Associated with Prion Disease

Maria Carmela Tartaglia, MD,1,2 Julie N. Thai, MSc,1,2 Tricia See, ScM,1,2 Amy Kuo, BSc,1,2 Robert Harbaugh, MD,4 Benjamin Raudabaugh, BSc,1,2 Ignazio Cali, MS,5 Mamta Sattavat, MS,3 Henry Sanchez, MD, PhD,3 Stephen J. DeArmond, MD, PhD,3 and Michael D. Geschwind, MD, PhD1,2

Abstract

Human prion diseases can be caused by mutations in the prion protein gene PRNP. Prion disease with mutations at codon 188 has been reported in 6 cases, but only 1 had the T188R mutation and it was not pathologically confirmed. We report the clinical, neuropsychological, imaging, genetic, and neuropathological features of a patient with familial Creutzfeldt-Jakob Disease (CJD), associated with a very rare PRNP mutation at T188R. The patient presented with prominent behavioral changes in addition to the more typical cognitive and motor impairments seen in sporadic CJD. The autopsy confirmed prion disease pathology. This case supports the pathogenicity of the T188 PRNP mutation, demonstrates the variability of clinical phenotypes associated with certain mutations and emphasizes the importance of testing for genetic prion disease in cases of apparently sporadic atypical dementia.

Keywords: Codon 188, Creutzfeldt-Jakob disease, Dementia, Genetic, Prion

INTRODUCTION

Although sporadic Creutzfeldt-Jakob disease (sCJD) accounts for the majority (~85%) of human prion disease cases, 10% to 15% of human prion diseases are inherited as autosomal dominant from human prion protein gene (PRNP) mutations. More than 55 different mutations (mostly point mutations) in PRNP are associated with genetic prion disease (1). Prion disease with mutations at codon 188 is exceedingly rare, with only 4 cases of T188K (threonine to lysine), 1 case of T188A (threonine to alanine) and 1 case of T188R (threonine to arginine) reported (2-5). T188K and T188R mutations in this highly conserved region of PRNP transform the amino acid from a polar uncharged moiety to a polar charged amino acid. Only a single case of T188K PRNP mutation has been pathologically confirmed, whereas the only other T188R case reported in the literature had no pathological confirmation. Here, we present a patient with prominent behavioral changes in addition to the more classical cognitive and motor impairments seen in sCJD. To our knowledge, this is the first autopsy-proven case caused by the T188R mutation.

MATERIALS AND METHODS

Clinical

The subject’s surrogate provided written, informed consent prior to participation in our rapidly progressive dementia clinical and research program. The University of California, San Francisco (UCSF) Committee on Human Research approved all study protocols. Neuropsychological assessment of language, memory, visuospatial, and executive function was performed. PRNP genetic testing was done through the National Prion Disease Pathology Surveillance Center, Cleveland, Ohio. Magnetic resonance imaging (MRI) scans were obtained on a 1.5T GE system equipped with a birdcage head coil. Structural MRI sequences as well as diffusion weighted images (DWI) and apparent diffusion coefficient (ADC) maps were obtained.

PRNP Genotype Determination

Genomic DNA was extracted and PRNP coding sequence was amplified and sequenced according to previously described primers and reagents (6-8).

Brain Homogenates Preparation and Western Blot Analysis

Brain tissue homogenates (10% wt/vol) were prepared as previously described (9) using 15% Tris-HCl gels (BioRad, Hercules, CA) and probed with monoclonal antibody 3F4 (courtesy of Stanley Prusiner, San Francisco, CA; 1:40,000). Prion protein was visualized on film (Eastman Kodak, Rochester, New York) using enhanced chemiluminescence (ECL Plus; GE Healthcare, Piscataway, NJ) as described by the manufacturer.

Neuropathology

The autopsy was performed 69 hours after death. The brain tissue was immersion-fixed in 10% buffered formalin for embedding in paraffin. Eight-μm-thick sections were stained with hematoxylin and eosin (H&E) to evaluate vacuolation. Reactive astrocytic gliosis was evaluated by glial fibrillary acidic protein (GFAP) immunostaining (anti-rabbit, 1:250, DAKO North America, Carpinteria, CA). Hydrolytic autoclaving pretreatment of the formalin-fixed tissue sections (to remove PrPC) was used to detect PrPSc with monoclonal antibody anti-3F4, as previously described (10). The Bielschowsky silver method and immunohistochemistry for α-synuclein (mouse monoclonal antibody, 1:1000, Millipore, Billerica, MA), tau (CP-13 antibody, courtesy of P. Davies, Albert Einstein College of Medicine, Bronx, NY), and TAR DNA-binding protein (TDP-43) (rabbit antibody, 1:2000, Proteintech Group, Chicago, IL), were used as needed to test for Alzheimer disease, synucleinopathies, tauopathies, and other neurodegenerative processes.

RESULTS

Case Description

The patient was a 55-year-old right-handed man who presented with rapid cognitive decline. A friend had first noticed a subtle change in his personality 4 months prior to initial presentation at UCSF when he had changed his long-standing beverage preference and began drinking sugared drinks, which was unusual in view of his diabetes. Over the next 2 months his friend noticed significant behavioral changes, including poor judgment (e.g. riding his bicycle in a field in the dark after not riding for more than 10 years), and delusions (e.g. believing his truck had spoken to him, trying to pay restaurants with cardboard credit cards). He developed a fear of being alone, often staying with a friend or family member. He forgot phone numbers and constantly misplaced objects. He repeated questions but did not answer them. He no longer understood sport scores, confused baseball and football, and could no longer cook, set the table, shave, or pick out his clothes. He was fired from work because he mistakenly came to work the midnight shift after completing the 5 AM to 3 PM shift, missed shifts, and could no longer do any calculations or follow job instructions. Over the following 3.5 months he first forgot his Social Security Number and soon after did not know what a Social Security Number was. A friend took over his finances because his bills were unpaid and he had exceeded his credit card limits. During the fourth month of symptoms he developed a delusion that a dog was talking to him. New behavioral changes included urinating outside a restaurant, loss of personal hygiene, (including playing with his feces), hoarding large amounts of pornography, consuming many sweets and having an insatiable appetite.

His relevant past medical history included hypercholesterolemia and hypertension, remote alcoholism but sober for more than 10 years, head injury from a motor vehicle accident in his 30s with loss of consciousness requiring resuscitation, and type 2 diabetes with onset in his 40s. He never smoked cigarettes, but had used recreational drugs, including marijuana, crack, cocaine, and LSD in the distant past.

His family history was somewhat unclear. His paternal grandfather died in his 50s following placement in a mental institution and he had 2 other paternal relatives with an acute onset, rapidly progressive illness with onset in their 50s (Fig. 1). His parents are in their 80s and able to participate in activities of daily living. His mother has memory complaints and increased anxiety that began later in life. His 4 siblings were all alive and in good health. The family is of Mexican-American origin.

Figure 1
Three-generation pedigree.

On initial physical exam at UCSF at 4 months after symptom onset he was an alert, well-groomed, perseverative gentleman who complied fully with the exam. His general physical exam was unremarkable. On cognitive testing, he had moderate to severe impairment in orientation, working memory, verbal and visual memory, calculations, and frontal-executive function, mild impairment on language function, and good performance on visual spatial tasks (Table). He denied depression. Cranial nerve exam revealed a possible decreased visual field in the right upper quadrant. Sensory exam revealed decreased sensation to vibration and pinprick in his lower extremities but normal joint position sense. Stereognosia was normal but there was subtle left hand agraphesthesia. Coordination was normal in the upper extremities but he had some left leg dysmetria. He had bilateral hand but no oral-buccal or leg apraxia. The rest of the neurological exam was normal.

Table
Neuropsychological Assessment at 4 Months after Symptom Onset

An extensive rapidly progressive dementia evaluation (11) was performed. Abnormal serological results included a positive anti-nuclear antibody (1:160) with homogeneous and speckled pattern and elevated serum anti-thyroglobulin antibodies, i.e. 92 and 96 IU/ml (normal <20). His complete blood count, electrolytes, rheumatologic, angiotensin converting enzyme, liver and thyroid function, Lyme serology, and HIV, RPR, HSV, and paraneoplastic encephalopathy antibody panel testing were normal or negative. Cerebrospinal fluid (CSF) showed an elevated protein at 95 mg/dL (normal <45) and mildly elevated IgG index of 0.57 (normal <0.5), but normal cells, glucose, protein and no oligoclonal bands. Abeta42 was elevated at 414.5 pg/ml, total tau was elevated at 2236.6 pg/ml, phosphorylated-tau 21.75 pg/ml, with an Abeta42-tau index = 0.14, reportedly not consistent with Alzheimer disease but consistent with CJD (Athena Diagnostics, Worcester, MA) (12-14). CSF 14-3-3 was weakly immunoreactive and “inconclusive” (National Prion Disease Pathology Surveillance Center). Neuron-specific enolase (Mayo Laboratories, Rochester, MN) was “intermediate” at 26 ng/ml (normal <15, indeterminate 15–35 and >35 elevated). Electroencephalogram (EEG) 4 months after symptom onset revealed diffuse slowing with superimposed focal slowing in the temporal lobe.

Brain MRI at 4 months revealed mild diffuse cortical atrophy, with moderate parietal atrophy and widening of the peri-sylvian fissures. On DWI, there was subtle hyperintensity in the caudate and putamen and subtle cortical ribboning (hyperintensity), in the anterior and medial temporal lobes, insula (left greater than right), bilateral frontal lobes, cingulate gyri and in one left posterior temporal gyri (Fig. 2A). The ADC maps showed hypointensity in several areas of corresponding DWI hyperintensity (Fig. 2B).

Figure 2
Axial diffusion weighted images (DWI) and apparent diffusion coefficient (ADC) maps magnetic resonance imaging sequences of the patient 4 months after symptom onset. (A) DWI shows pathologic hyperintensity in bilateral frontal neocortex, supplementary ...

At 8 months after onset he needed assistance with all activities of daily living and was in a fullcare facility. He had stopped recognizing his sister 1 month prior but was still able to recognize his parents and brother. He had severe semantic deficits and was almost mute and extremely apathetic. He had myoclonus and severe apraxia and exhibited restlessness with repetitive behaviors (often picking at his clothes and sheets), and was completely incontinent. In the last 2 months before death he was bedbound with seizures. He died 14 months after symptom onset. The general autopsy showed aspiration pneumonia, diabetic nephropathy and chronic pancreatitis due to past alcoholism.

Genetics

PRNP genetic testing revealed a missense mutation (T188R), resulting in a threonine (ACG) to arginine (AGG) change at codon 188, with codon 129 methionine (M)/valine (V)(valine cis). His father, aged 80, and his brother, aged 56, carry the same mutation but are currently asymptomatic. His father is also MV at codon 129 but his brother is VV.

Western Blot Analysis

Western blot analysis of brain homogenates from cerebral cortex revealed a type I PrPSc pattern (Fig. 3, lane 2), similar to the type 1 pattern of an sCJD case (MM1, Fig. 3, lane 3).

Figure 3
Western blot analysis of brain homogenates from cerebral cortex and probed with antibody 3F4 before (lane 1) and after (lanes 2-4) digestion with protease K (PK). The electrophoretic migration of the unglycosylated PK-resistant PrPSc from fCJD T188R is ...

Neuropathology

The fresh brain weighed 1450 g. Gross examination revealed severe symmetric atrophy of the frontal and parietal lobes and of the left temporal lobe and there was softening in the anterior left temporal lobe due to severe degeneration. There were spongiform stages in H&E stains in the frontal (Fig. 4A), parietal, superior temporal gyrus, entorhinal cortex, and insula. This was contrasted with a severe loss of neurons, reactive astrogliosis and extracellular slit-like spaces resembling status spongiosus seen in the inferior temporal gyrus (Fig. 4B).

Figure 4
Postmortem neuropathological findings. (A) Spongiform changes in the frontal cortex (H&E, original magnification 20x); (B) Status spongiosus-like degeneration in the inferior temporal cortex (H&E, original magnification 20x); (C) Severe ...

Early status spongiosus-like changes were observed in the cingulate. Vacuolation was moderate in the amygdala, hippocampus and occipital lobe, mild to moderate in the caudate, and mild in the frontal lobe, striatum, pons (periaqueductal gray and locus coeruleus) and cerebellum. There was marked reactive astrocytic gliosis in the frontal and parietal lobes, superior and inferior temporal gyri (Fig. 4C), entorhinal cortex and subiculum, transentorhinal cortex, hippocampus CA3 with sparing of CA1, CA2, CA4 and dentate gyrus. The cingulate, caudate, and insula showed marked gliosis. There was moderate gliosis in the thalamus, amygdala and minimal gliosis in the pons. There was a marked loss of neurons and collapse of tissue in many frontal and temporal lobe regions and in the cingulate. The hippocampus showed mild to moderate cell loss and no neurofibrillary tangles.

In addition to the typical PrPSc synaptic staining pattern of sCJD there were also patches of plaque-like deposits throughout most of the sampled brain including all of the cortex (Fig. 4D), cingulate, caudate, putamen, insula, amygdala, hippocampus, transentorhinal cortex, entorhinal cortex, subiculum, thalamus, and cerebellar molecular layer (Fig. 4E). There was also considerable cell loss in the cerebellar granule cell layer. Intense Bergmann radial gliosis (Fig. 4F) was seen throughout the molecular layer of the cerebellum; Purkinje cells were generally preserved. There was moderate atrophy of cerebellar white matter with some pallor of the dentate fiber tracts. Ballooned neurons were observed in all cortical regions. Some of the ballooned neurons contained PrPSc+, tau-negative cytoplasmic inclusions (Fig. 5). The hippocampus, entorhinal cortex and inferior temporal cortex were stained with Gallyas and Bielschowsky techniques and by immunohistochemistry for tau and TDP-43. Negative results indicated that there was no evidence of Alzheimer disease or frontotemporal lobar degeneration.

Figure 5
Immunohistochemistry with 3F4 antibody against PrP shows ballooned neurons with PrPSc+ cytoplasmic inclusions in inferior temporal cortex (40x). Hematoxylin counterstain. Scale bar = 20 μm.

DISCUSSION

This is the second patient with a T188R PRNP mutation described in the literature and the first with autopsy-proven CJD. He presented with a subacute, progressive dementia affecting behavior, memory, executive function, and language, but largely sparing his visuospatial and motor function. He did not meet possible or probable sCJD criteria according to World Health Organization (WHO) criteria (i.e. dementia plus 2 of the following: myoclonus, pyramidal/extrapyramidal signs, visual/cerebellar signs, akinetic mutism and typical EEG or CSF 14-3-3 if duration less than 2 y [15, 16]), nor new European possible or probable sCJD criteria, (same as WHO, but allowing the use of MRI) (17). He did meet UCSF probable sCJD criteria (18) due to his rapid dementia, mild cerebellar signs and higher focal cortical sign of apraxia, in addition to DWI/ADC MRI findings (19). The patient presented with behavioral signs including eating habit changes, poor judgment, lack of insight, disinhibition, loss of disgust, decline in personal hygiene in association with memory and executive impairments. He did not meet Neary criteria for behavioral variant frontotemporal lobar degeneration because of the rapid progression of his symptoms (20). The other reported patient with the same mutation was a 66-year-old old who presented with progressive visual impairment followed several months later by progressive dementia and mild ataxia (2, 5, 21), a clinical picture different from our case.

The neuropathology examination demonstrated spongiform changes consisting of intracellular vacuolation (especially in dendrites) in numerous brain regions. There were additional status spongiosus-like changes with marked neuronal loss and reactive gliosis and extracellular slit-like spaces in the inferior temporal gyrus. This is a late finding suggesting severe disease and was also described along with ballooned neurons in the T188K case (5). The PrPSc staining in our case, however, differed from what was described in the T188K case in that the pattern was patchy and plaque-like, in addition to a synaptic pattern (5).

Although sCJD usually displays characteristic MRI findings (restricted diffusion greater in the cerebral cortex and/or basal ganglia/thalamus), genetic prion diseases are less consistently associated with these MRI findings. Whereas mutations such as V180I, E200K, T183A, and I210V can show brain MRI findings similar to sCJD (22-24), many PRNP mutation diseases do not show these characteristic features (19). In 2 of 4 T188K cases there were MRI findings consistent with sCJD, i.e. 1 with T2-hyperintensity in the striatum and the other with diffusion abnormalities in the cortex. It is not known whether the other T188 cases had the appropriate FLAIR, DWI and ADC sequence studies performed (17, 19). Our patient had some subtle DWI/ADC MRI features that are seen in sCJD (19), but there was also marked cortical atrophy. The EEG in our patient only demonstrated diffuse slowing, unlike the previously reported T188R patient who showed typical periodic sharp-wave complexes (PSWCs) on EEG examination. This might be due to our assessment having been done at an earlier time point in the disease course; PSWCs in sCJD are usually a later finding (25).

The previous T188R patient had no known family history of dementing illnesses, but her father had succumbed to pleuritis at age 31 years. PRNP testing revealed that our patient’s father and 1 sibling, both of whom are asymptomatic, have the same T188R mutation. Some PRNP mutations exhibit reduced penetrance, as suggested by the proportion of genetic CJD cases (5%–88%, depending on the mutation), with a negative family history (26, 27). Our findings suggest either reduced penetrance with the T188R mutation or that the pathogenic effect depends on additional factors (28, 29). Codon 129 polymorphism is known to exert an influential role in both sporadic and genetic prion disease (30). In view of the fact that our patient’s father is also MV and is still unaffected at age 80 years, it is unclear what the influential factor is in this case. Furthermore, the previously described T188R case was VV (5), i.e. different from our patient. It also appears that the T188K mutation is not fully penetrant because at least one 79-year-old person with the mutation did not show any evidence of disease (5).

There are several arguments that strongly support a pathogenic role for T188R and T188K mutations. The T188K mutation was observed in 4 CJD patients that were confirmed pathologically in one case. None of 735 healthy controls screened carried these mutations. Moreover, threonine at codon 188 of PRNP is highly conserved throughout all mammals, indicating that these mutations are likely to have a dramatic effect on the function of the prion protein (31, 32). Codon 188 is located in the C-terminal half of the second α-helix, a highly structured part of the protein; the substitution of threonine for a highly basic amino acid such as arginine (T188R) or lysine (T188K) would result in structural destabilization (5). Cell culture studies have demonstrated that PrP T188R mutants had enhanced resistance to proteinase K (33). Curiously, 1 patient with a T188A mutation had all of the pathological and clinical features of prion disease, except that his PrPSc immunohistochemistry was negative (34). This might be explained by T188A causing a prionopathy with largely protease sensitive PrPSc.

The present case further supports the pathogenicity and adds to our clinical, radiological and pathological understanding of the T188 PRNP mutation. It also illustrates that certain mutations may present with very different clinical phenotypes. Lastly, our case emphasizes the importance of testing for genetic prion disease in any patient presenting with atypical dementia, such as early onset dementia, even in the absence of a positive family history (35).

ACKNOWLEDGMENTS

We would like to thank the patient and his family for their participation in research. The authors would like to thank the National Prion Disease Pathology Surveillance Center for Western blot analysis, CSF 14-3-3 and PRNP genetic testing.

This work was supported by National Institutes of Health, National Institute on Aging (NIH/NIA) K23 AG021989 and R01-AG031189 grants and the Michael J Homer Family fund. MCT is supported by Fonds de la recherche en santé du Québec.

Footnotes

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