Gerstmann‐Sträussler‐Scheinker Syndrome with Variable Phenotype in a New Kindred with PRNP‐P102L Mutation

Abstract

Gerstmann‐Sträussler‐Scheinker syndrome (GSS) is a dominantly inherited disorder belonging to the group of transmissible human spongiform encephalopathies or prion diseases. Several families affected by GSS with patients carrying mutations in the prion protein gene have been described worldwide. We report clinical, genealogical, neuropathology and molecular study results from two members of the first Argentine kindred affected by GSS. Both family members presented a frontotemporal‐like syndrome, one with and the other without ataxia, with different lesions on neuropathology. A Pro to Leu point mutation at codon 102 (P102L) of the prion protein gene was detected in one of the subjects studied. The pathogenic basis of phenotypic variability observed in this family remains unclear, but resembles that observed in other P102L GSS patients from the same family.

Introduction

Transmissible human spongiform encephalopathies or prion diseases encompass a spectrum of disorders including sporadic, variant and genetic Creutzfeldt‐Jakob disease (CJD), sporadic and familial fatal insomnia, kuru and Gerstmann‐Sträussler‐Scheinker syndrome (GSS). These disorders are characterized by the deposition, mainly in the brain, of an abnormal isoform of the host prion protein (PrP) 24. About 10–15% of human prion diseases are dominantly inherited, including 100% of GSS cases and approximately 10–15% of CJD cases 19.

As GSS was first described in an Austrian family in 1936 6, 10, 11, families suffering from the disorder have been identified in 10 different countries worldwide 12, 18, 26. All GSS cases are linked to mutations in the prion protein gene (PRNP), with the proline to leucine substitution at residue 102 (P102L) 15 being the most common one 5 among others previously described 21.

GSS patients develop the disease relatively early [mean age 51.6 years, standard deviation (SD) 12.8 years] with a long clinical duration (mean 40 years, SD 25 months) 16, characterized in most cases by progressive cerebellar ataxia accompanied by cognitive decline 9. However, GSS patients may have different clinical phenotypes ranging from almost pure cerebellar signs without dementia, psychiatric manifestations at onset followed by ataxia 3, slowly progressive dementia (frontotemporal‐like) 29, or with clinical features resembling sporadic CJD 2.

Neuropathological examination reveals the presence of abundant multicentric amyloid plaques in the cerebellar and cerebrum cortices, with variable amount of spongiform changes, ranging from complete absence to severe spongiform changes 2, 9.

This study reports an Argentine family whose members carry the P102L mutation of the PRNP gene. This is the first GSS kindred observed, to our knowledge, in a Latin American country.

Materials and Methods

Family history and clinical assessment

Clinical histories and examination details were obtained from medical notes completed at the time of clinical review. Family history and complementary clinical information were obtained from alive and healthy members of the kindred (Figure 1). Informed consent for genetic analyses and brain autopsy were obtained from the next of kin. This study was approved by the Ethical Committee of FLENI, Buenos Aires, Argentina.

Figure 1.

Family pedigree. Solid symbols indicate individuals with autopsy; stripped symbols reflect individuals affected by a neurological disorder; and diagonal lines, those who are deceased. The arrow singles out the proband.

Neuropathological assessment

The purpose and procedures of the autopsy were explained and objectives discussed with the relatives. We performed the autopsy on the proband (subject IV‐7). Cerebrum, brain stem and cerebellum were available. A piece of frontal cortex was taken fresh and was frozen in −80°C.

The brain was fixed in 10% formaldehyde, and cut 2 weeks after fixation. Samples of fixed tissue were obtained from the frontal, temporal, parietal and occipital cortices, as well as from the hippocampal formation, basal ganglia, thalamus, cerebellum and brain stem.

The cerebrum from subject IV‐5 was received as a consult. Samples were obtained from the frontal, temporal, parietal and occipital cortices, as well as from the hippocampal formation, basal ganglia and thalamus. The tissue was processed for paraffin embedding and 10‐μm thick sections stained with hematoxylin and eosin (H&E), and immunostained for the pathological prion protein (PrP^TSE) (3F4. 1:500 after 88% formic acid treatment).

PRNP gene sequencing

DNA was extracted from frozen brain tissue (proband, IV‐7) using the Wizard Genomic DNA Purification kit (Promega Corporation, Fitchburg, WI, USA) and from paraffin embedded/formalin fixed brain tissue (patient IV‐5) using the DNeasy Blood and Tissue Kit (Qiagen, Venlo, Limburg, Netherlands). We genotyped the P102L mutation by direct Sanger sequencing as previously described 19. To verify the presence of the mutation on the Met allele, we have first cloned the fragment by thymine‐adenine cloning (Invitrogen, Carlsbad, CA, USA) and then sequenced clones.

Results

Family description

The family (Figure 1) was originally from a small village in Sicily (San Piero, Messina), who later left Italy to settle in Argentina (near Buenos Aires) in the early XXth century.

The proband (IV‐7, Figure 1) was a 50‐year‐old physician who, in 2001 at age 44, referred abnormal gait suggestive of ataxia. In 2002, a neuropsychological examination was within normal limits; however, electromyography (EMG) results reported an axonal pattern, and brain magnetic resonance imaging (MRI) indicated high signal intensity in the basal ganglia (Figure 2B). Some months later, the patient progressed with cognitive decline mainly with a frontotemporal pattern consisting of disinhibited, repetitive and compulsive behaviors. Over the following years, it evolved with aphasia and added agnosia, sphincter incontinence, amyotrophy, apraxia, difficulty in swallowing and finally bronchopneumonia and sepsis. The patient died in early 2007 and an autopsy was performed in our unit.

Figure 2.

MRI from subject IV‐5—performed at the age of 42, during the first year of the disease A, and from the proband—performed at the age of 46, during the second year of the disease. Axial FSE T2‐weighted images disclosed, in both cases, fine bilateral bright signal enhancement in the basal ganglia, more conspicuous in Figure B.

Subject IV‐5: In 2000, this 41‐year‐old computer technician experienced neurological impairment mainly with a frontotemporal pattern imparted by the presence of cognitive decline with disinhibited behavior and attentional deficits. At that time, the mini‐mental state examination score was 23/30. During the ensuing years, the patient developed passivity, aphasia, memory loss and agnosia, although on neurological examination, no ataxia or pyramidal/extrapyramidal signs were evident. EMG performed in 2001 showed no relevant abnormalities. Brain MRI indicated high signal intensity in the basal ganglia but no further alterations in cortical or subcortical regions (Figure 2A). The patient finally died in 2004 with a clinical diagnosis of Pick's disease at the age of 45 in his death certificate. Autopsy was performed, and the brain, without the cerebellum and the brain stem, was referred to our brain bank in Buenos Aires.

Scant clinical information is available for the other members of the family. However, according to reports from relatives, the father (III‐1) of the GSS patient IV‐5 died in 1978 with a clinical diagnosis of dementia with motoneuron signs, and his father (II‐1) had in turn been wheelchair‐bound. As both of them were obligate carriers, it is likely that he died of GSS.

On the other side of the family, the brother (IV‐6) of the proband died in 2002 at 52 years with a clinical diagnosis of frontotemporal dementia with motoneuron signs, the father (III‐3) had died in 1976 at age 54 with a clinical diagnosis of dementia with motoneuron signs, while their grandmother (II‐3) in 1956 at age 52 with a clinical diagnosis of Pick's disease. The father and the grandmother were obligate carriers and it is conceivable that both of them were affected by GSS.

Although we cannot formally prove that the brother of the proband carried the P102L mutation, his clinical signs strongly suggest that he did. An aunt (III‐4) and an uncle (III‐5) of the proband died at age 42 because of leukemia and at age 33 because of the disruption of an aortic aneurysm, respectively. Subject II‐2 moved from Argentina to another country and we have been unable to retrieve the age of death and/or clinical diagnosis. No information was available for subjects I‐1 and I‐2, and therefore, we cannot speculate who was the mutated carrier.

Neuropathology

The cerebrum from the proband revealed spongiform changes only in the superficial layers (I‐III) in occipital cortex, and widespread in the remaining cortices and striatum (Figure 3A and B). Multiple multicentric and unicentric PrP‐positive plaques were observed in the neocortex (Figures 3A and E), the amygdala (Figure 3F), the hippocampus, the cerebellum, the basal ganglia (present more prominently in the globus pallidus) and occasionally in all layers of the enthorhinal cortex (Figure 3H). Synaptic PrP‐positive deposits were also observed in the dentate gyrus, stratum moleculare 1, in the Ammon's horn, stratum radiatum. (Figure 3C) and through the molecular, Purkinje and granular layers of the cerebellum (Figure 3D and I).

Figure 3.

Neuropathology examination of brain tissue from the proband. A. Spongiform changes in cortical layers; also multicentric (thin arrow) and unicentric/kuru‐like (thick arrow) amyloid plaques are noticed (temporal cortex, H&E, 200×). B. Significant spongiform changes in basal ganglia (putamen, H&E, 200×). C. Unicentric and multicentric deposits of PrP in the Ammon's horn and in the dentate gyrus (CA1 level, immunostain for PrP, 100×). D. Presence of amyloid plaques in the molecular, Purkinje (thick arrow) and granular layers of the cerebellum (H&E, 200×). E. Cortical PrP‐positive deposits in layers II and III (plaques) and layer I (synaptic) (temporal cortex, immunostain for PrP, 200×). F. Unicentric and multicentric PrP‐positive deposits in the amygdala (immunostain for PrP, 200×). G. Globus pallidus displaying multiple PrP‐positive deposits (immunostain for PrP, 200×). H. Entorhinal cortex displaying occasional PrP‐positive deposits (PrP, 40×). I. Multicentric PrP‐positive deposits throughout the cerebellar cortex (immunostain for PrP, 200×). AHSR = Ammon's horn stratum radiatum; DSM1 = dentate gyrus stratum moleculare 1; SG = stratum granulosum.

Histological analyses on subject IV‐5 showed occasional multicentric plaques in the neocortex and multiple plaques in the amygdala on the H&E staining (Figure 4A and B). Prion protein immunostaining revealed multiple plaque‐like PrP‐positive deposits in the Ammon's horn stratum moleculare and stratum radiatum (Figure 4C), small plaques and occasional synaptic deposits in the neocortex (Figure 4D), multiple unicentric and occasional multicentric plaques in the amygdala (Figure 4E) and PrP‐positive synaptic deposits in the superficial and deeper layer of the entorhinal cortex (Figure 4F). Neither brain stem nor cerebellum was available for examination. Frozen material was not available for PRNP sequencing.

Figure 4.

Neuropathologic examination of cerebrum from subject IV‐5. A. An isolated multicentric amyloid plaque (small arrow) is noticed (temporal cortex, H&E, 200×). B. Multiple unicentric/kuru‐like amyloid plaques (thick arrow) are appreciated in the amygdala (H&E, 200×). C. Unicentric plaques and synaptic PrP‐positive deposits in the Ammon's horn (CA1 level, immunostain for PrP, 40×). D. Occasional PrP‐positive (small arrow) cortical deposits (temporal cortex immunostain for PrP, 200×). E. PrP‐positive multicentric (thin arrow) and kuru‐like (thick arrow) plaques in the amygdala (immunostain for PrP, 200×). F. Entorhinal cortex displaying multiple PrP‐positive deposits (immunostain for PrP, 40×). AHSM = Ammon's horn stratum moleculare; AHSR = Ammon's horn stratum radiatum; HS = hippocampal sulcus; SG = stratum granulosum.

PRNP gene sequencing

Complete sequencing of the PRNP coding region of the proband revealed the presence of a T to C mutation in one allele at the second position of codon 102, which results in the substitution of proline by leucine. The mutated allele contained the triplet ATG (methionine) at codon 129 while the nonmutated allele had GTG (valine). Both alleles had the triplet GAG (glutamic acid) at codon 219. We were not able to detect the mutation in DNA extracted from paraffin‐embedded tissue (subject IV‐5); however, it is likely that this patient carried the P102L mutation of the PRNP gene.

Discussion

In the family described in this work, the proband had clinical features of frontotemporal dementia with ataxia, and neuropathological features of GSS, and carried the pathogenic mutation at codon 102 of the PRNP gene. A distant relative (IV‐5) also had clinical features of frontotemporal dementia and neuropathological features of GSS, and although we could not detect the mutation probably because of the degree of degradation 7, it is suggestive that he also carried the P102L mutation.

Although clinical data for the other obligate mutation carriers (IV‐6, III‐1, III‐3, II‐1 and II‐3) is scant and no autopsy material was available, they also developed a neurodegenerative disorder in their 50s years, which is highly suggestive of GSS. Family members of generations I and II were born in Southern Italy (a small town in the province of Messina, Sicily) where several apparently unrelated families experienced GSS in carriers with the P102L mutation 2, 3, 8, 13, 17, 19. It is therefore likely that this family is related to one of the previously described GSS‐affected families in Sicily and work is in progress to identify a possible common ancestral origins of the P102L mutation‐associated chromosomes in these families through genealogical 4 and genetic studies 20.

Both the proband (IV‐7) and IV‐5 had clinical signs resembling FTD but the former showed also ataxia while IV‐5 did not. Differences in clinical signs and disease duration of P102L‐GSS patients have been previously observed, even within the same family, where cases might resemble sporadic CJD, have pure cerebellar signs with no dementia or psychiatric disturbances 1, 2, 3, 14, 22, 27, 28. The proband and IV‐5 also had different neuropathological patterns. Spongiform changes ranged from moderate to prominent in the proband while were almost absent in subject IV‐5. PrP^TSE staining pattern also showed marked differences in these two autopsied family members (see Figures 3 and 4). The reason for this variability remains poorly understood and it is still controversial whether it depends on the presence of methionine or valine in the polymorphic codon 129 of the nonmutated PrP allotype 2, 27, different patterns of truncated prion protein fragments 22 or prion protein heterogeneity 23, 25.

Once clinical suspicion arises, cases potentially considered to be caused by prions are normally referred to the Centre for Human Transmissible Spongiform Encephalopathies (HTSE), functioning at our institution since 1983, where patients are studied extensively, with workup including electroencephalography (EEG), MRI and 14‐3‐3 protein WB in CSF. However, on a limited number of occasions, a few prion‐related cases presenting clinically with symptoms of more common neurodegenerative disorders may escape this tight surveillance system and be handled at autopsy as “standard” cases. The material will therefore be sent to the brain bank instead of the Centre for HTSE. Within the group of prion‐related diseases, this holds true especially for Gerstmann‐Sträussler‐Scheinker syndrome.

It is important to acknowledge that the identification of this kindred would have been missed by routine clinical and laboratory investigations suggesting that PRNP genetic analyses and post‐mortem examination should be recommended in all cases with a family history of any type of neuropsychiatric syndrome 27, even when they are not associated with cognitive signs.

In conclusion, we report the first Argentine kindred affected by Gerstmann‐Sträussler‐Scheinker disease associated with the P102L mutation of the PRNP gene, with possible intrafamilial clinical variability and Italian origins.