Atypical tauopathy with massive involvement of the white matter

The many faces of globular glial tauopathy: A clinical and imaging study

BACKGROUND

Globular glial tauopathy (GGT) has been associated with frontotemporal dementia syndromes; little is known about the clinical and imaging characteristics of GGT and how they differ from other non-globular glial 4-repeat tauopathies (N4GT) such as progressive supranuclear palsy (PSP) or corticobasal degeneration (CBD).

METHODS

For this case-control study the Mayo Clinic brain banks were queried for all cases with an autopsy-confirmed diagnosis of GGT between 1 January 2011 and 31 October 2021. Fifty patients with N4GT (30 PSP, 20 CBD) were prospectively recruited and followed by the Neurodegenerative Research Group at Mayo Clinic, Minnesota. Magnetic resonance imaging was used to characterize patterns of gray/white matter atrophy, MR-parkinsonism index, midbrain volume, and white matter hyperintensities.¹⁸ F-Fluorodeoxyglucose-, ¹¹ C Pittsburg compound-, and ¹⁸ F-flortaucipir-positron emission tomography scans were reviewed.

RESULTS

Twelve patients with GGT were identified: 83% were women compared to 42% in NG4T (p = 0.02) with median age at death 76.5 years (range: 55-87). The most frequent clinical features were eye movement abnormalities, parkinsonism, behavioral changes followed by pyramidal tract signs and motor speech abnormalities. Lower motor neuron involvement was present in 17% and distinguished GGT from NG4T (p = 0.035). Primary progressive apraxia of speech was the most frequent initial diagnosis (25%); 50% had a Parkinson-plus syndrome before death. Most GGT patients had asymmetric frontotemporal atrophy with matching hypometabolism. GGT patients had more gray matter atrophy in temporal lobes, normal MR-parkinsonism index, and larger midbrain volumes.

CONCLUSIONS

Female sex, lower motor neuron involvement in the context of a frontotemporal dementia syndrome, and asymmetric brain atrophy with preserved midbrain might be suggestive of underlying GGT.

Association Between Globular Glial Tauopathies and Frontotemporal Dementia-Expanding the Spectrum of Gliocentric Disorders: A Review

Importance

Globular glial tauopathies (GGTs), as defined by a consensus study in 2013, belong to the group of frontotemporal lobar degenerations and expand the spectrum of glial-predominant neurodegenerative diseases. Three neuropathological subtypes of GGT (types I-III) are characterized by phosphorylated tau-immunopositive inclusions that are predominantly in oligodendroglia and/or astroglia in the frontal, temporal, and/or precentral cortices. Type II is largely restricted to the corticospinal system. The low incidence of GGT (<10% of cases of frontotemporal lobar degeneration with tau pathology), together with its unusual combination of neuronal and nonneuronal pathology, has hindered identification and accurate diagnosis. This review collated clinical, demographic, neuropathological, and genetic data from 88 published GGT cases identified on PubMed to examine the association between GGT and frontotemporal dementia and associated disorders.

Observations

Among 88 patients with GGT (46 female [52.3%]; mean [SD] age at disease onset, 65 [11] years), 44 patients (50.0%) had idiopathic disease, and 21 patients (23.9%) had a variation in the microtubule-associated protein tau (MAPT) gene. Those with idiopathic GGT compared with those with a variation in MAPT had a mean (SD) age at symptom onset of 70 (8) years vs 54 (9) years and a mean (SD) disease duration of 7 (3) years vs 6 (3) years, respectively. A similar sex distribution was observed among patients with GGT; however, female patients were typically 6 years older at symptom onset than male patients (mean [SD] age, 68 [11] years vs 62 [11] years, respectively). Disease duration was similar in both sexes (mean [SD], 6 [3] years for women and 6 [4] years for men). The most common predominant clinical features were primary progressive aphasia (22 patients [25.0%]), behavioral-variant frontotemporal dementia (20 patients [22.7%]), upper motor neuron signs (11 patients [12.5%]), memory impairment (7 patients [8.0%]), and Richardson syndrome (7 patients [8.0%]). Although some demographic differences between GGT subtypes were identified, the predictive value of the clinical presentation was low, calling into question the need for neuropathological subtyping. Further neuropathological studies are needed to clarify whether GGT type II should be interpreted as atypical progressive supranuclear palsy or a separate entity. Few cases (7 patients [8.0%]) had coexisting proteinopathies.

Conclusions and Relevance

This review of the published data suggests an association between regional distribution of glial tau pathology and neuronal degeneration. Targeting glial tau accumulation or sustaining their neuron-supportive function might require different therapeutic or neuroprotective strategies and more accurate preclinical models to explore disease mechanisms and track progression. Emerging data support the important role of glia in the pathogenesis of neurodegenerative disorders, highlighting the need to raise awareness of GGT in clinical and research settings.

Globular glial tauopathy Type I presenting with behavioral variant frontotemporal dementia

Globular glial tauopathy (GGT) is a recently proposed tauopathy characterized by the globular accumulation of four-repeat (4R) tau in the oligodendroglia (globular oligodendroglial inclusion (GOI)) and astrocytes (globular astrocytic inclusion (GAI)), in addition to deposition in neurons. Although it is proposed that GGT should be classified into three different neuropathological subtypes, previous reports have indicated that subclassification might be difficult in some cases. We report an autopy case of a 79-year-old man with behavioral variant frontotemporal dementia (bvFTD). He developed behavioral changes at 67 years of age and had auditory hallucinations and persecutory delusions at admission to a psychiatric hospital at 69 years of age. Neuropathologically, marked atrophy of the frontotemporal lobes and severe degeneration of the white matter and frontopontine tract were observed. The present case corresponded to GGT Type I, as numerous GOIs were observed, predominantly in the frontotemporal region. However, concurrent degeneration of the motor cortex and corticospinal tract suggest characteristics of Type II. Although the relationship between psychotic symptoms and GGT remains unclear, the present case demonstrates heterogeneity of GGT subtypes.

Involvement of Oligodendrocytes in Tau Seeding and Spreading in Tauopathies

Introduction: Human tau seeding and spreading occur following intracerebral inoculation into different gray matter regions of brain homogenates obtained from tauopathies in transgenic mice expressing wild or mutant tau, and in wild-type (WT) mice. However, little is known about tau propagation following inoculation in the white matter. Objectives: The present study is geared to learning about the patterns of tau seeding and cells involved following unilateral inoculation in the corpus callosum of homogenates from sporadic Alzheimer's disease (AD), primary age-related tauopathy (PART: neuronal 4Rtau and 3Rtau), pure aging-related tau astrogliopathy (ARTAG: astroglial 4Rtau with thorn-shaped astrocytes TSAs), globular glial tauopathy (GGT: 4Rtau with neuronal tau and specific tau inclusions in astrocytes and oligodendrocytes, GAIs and GOIs, respectively), progressive supranuclear palsy (PSP: 4Rtau with neuronal inclusions, tufted astrocytes and coiled bodies), Pick's disease (PiD: 3Rtau with characteristic Pick bodies in neurons and tau containing fibrillar astrocytes), and frontotemporal lobar degeneration linked to P301L mutation (FTLD-P301L: 4Rtau familial tauopathy). Methods: Adult WT mice were inoculated unilaterally in the lateral corpus callosum with sarkosyl-insoluble fractions or with sarkosyl-soluble fractions from the mentioned tauopathies; mice were killed from 4 to 7 months after inoculation. Brains were fixed in paraformaldehyde, embedded in paraffin and processed for immunohistochemistry. Results: Tau seeding occurred in the ipsilateral corpus callosum and was also detected in the contralateral corpus callosum. Phospho-tau deposits were found in oligodendrocytes similar to coiled bodies and in threads. Moreover, tau deposits co-localized with active (phosphorylated) tau kinases p38 and ERK 1/2, suggesting active tau phosphorylation of murine tau. TSAs, GAIs, GOIs, tufted astrocytes, and tau-containing fibrillar astrocytes were not seen in any case. Tau deposits were often associated with slight myelin disruption and the presence of small PLP1-immunoreactive globules and dots in the ipsilateral corpus callosum 6 months after inoculation of sarkosyl-insoluble fractions from every tauopathy. Conclusions: Seeding and spreading of human tau in the corpus callosum of WT mice occurs in oligodendrocytes, thereby supporting the idea of a role of oligodendrogliopathy in tau seeding and spreading in the white matter in tauopathies. Slight differences in the predominance of threads or oligodendroglial deposits suggest disease differences in the capacity of tau seeding and spreading among tauopathies.

Atypical globular glial tauopathy with a combination of types I and II pathology

Globular glial tauopathy (GGT) is a group of 4-repeat tauopathies characterized by widespread globular glial inclusions (GGIs). GGT is now classified into three subtypes based on the distribution and morphology of the GGIs. We report an autopsy case of GGT in an 85-year-old woman who presented with semantic dementia, a rare phenotype in GGT. Postmortem examination revealed marked atrophy of the frontotemporal and motor cortices and corticospinal tract degeneration with widespread occurrence of globular neurofibrillary tangles and GGIs. The distribution of the pathology was similar to that seen in GGT type III. However, the morphology of astrocytic inclusions in the present case differed from that in type III. Moreover, the tau burden in the primary motor area was more severe in the gray than in the white matter, and globular oligodendroglial inclusions were more numerous than astrocytic inclusions, corresponding to GGT type II. By contrast, the tau pathology in the temporal lobe was chiefly globular oligodendroglial inclusions in the white matter, corresponding to GGT type I. Thus, the present case exhibited a combination of GGT types I and II pathology. Our findings appear to extend the pathological heterogeneity of GGT.

Astrogliopathy in Tauopathies

Astrocytes are involved in many diseases of the central nervous system, not only as reactive cells to neuronal damage but also as primary actors in the pathological process. Astrogliopathy is a term used to designate the involvement of astrocytes as key elements in the pathogenesis and pathology of diseases and injuries of the central nervous system. Astrocytopathy is utilized to name non-reactive astrogliosis covering hypertrophy, atrophy and astroglial degeneration with loss of function in astrocytes and pathological remodeling, as well as senescent changes. Astrogliopathy and astrocytopathy are hallmarks of tauopathies—neurodegenerative diseases with abnormal hyper-phosphorylated tau aggregates in neurons and glial cells. The involvement of astrocytes covers different disease-specific types such as tufted astrocytes, astrocytic plaques, thorn-shaped astrocytes, granular/fuzzy astrocytes, ramified astrocytes and astrocytes with globular inclusions, as well as others which are unnamed but not uncommon in familial frontotemporal degeneration linked to mutations in the tau gene. Knowledge of molecular differences among tau-containing astrocytes is only beginning, and their distinct functional implications remain rather poorly understood. However, tau-containing astrocytes in certain conditions have deleterious effects on neuronal function and nervous system integrity. Moreover, recent studies have shown that tau-containing astrocytes obtained from human brain tauopathies have a capacity for abnormal tau seeding and spreading in wild type mice. Inclusive conceptions include a complex scenario involving neurons, glial cells and local environmental factors that potentiate each other and promote disease progression in tauopathies.

An autopsy case of globular glial tauopathy presenting with clinical features of motor neuron disease with dementia and iron deposition in the motor cortex

Globular glial tauopathy (GGT) is a 4-repeat (4R) tauopathy in which 4R tau accumulates to form globular glial inclusions (GGIs), predominantly in oligodendroglia. To date, little has been reported on iron deposits in patients with GGT. We report a case of GGT with iron deposits in a 78-year-old woman presenting with an 8-year history of slowly progressing limb weakness and cognitive decline. Susceptibility-weighted imaging revealed a low signal intensity in the right precentral gyrus, suggesting iron deposition. A clinical diagnosis of motor neuron disease with dementia was made 4 years after onset. At autopsy, gross pathological findings showed atrophy of the frontal and temporal lobes. A localized area of the precentral gyrus corresponding to the most severely affected limb showed the strongest atrophy, macroscopically, and displayed 4R tau-immunoreactive GGIs and microscopically many ferritin-immunoreactive neurons. We diagnosed this patient as having GGT. This is the first GGT case with iron deposition confirmed both radiologically and pathologically.

Expanding the phenotypic associations of globular glial tau subtypes

Introduction

Clinicopathologic correlation in non-Alzheimer's tauopathies is variable, despite refinement of pathologic diagnostic criteria. In the present study, the clinical and neuroimaging characteristics of globular glial tauopathy (GGT) were examined to determine whether subtyping according to consensus guidelines improves clinicopathologic correlation.

Methods

Confirmed GGT cases (n = 11) were identified from 181 frontotemporal tauopathy cases. Clinical and neuroimaging details were collected, and cases sub-typed according to the consensus criteria for GGT diagnosis. Relationships between clinical syndrome and GGT subtype were investigated.

Results

In total, 11 patients (seven males, four females, mean age = 67.3 +/− 10.6 years) with GGT were included. Most, but not all, presented with behavioral variant frontotemporal dementia, but none had amyotrophic lateral sclerosis. Subtyping of GGT proved to be difficult and did not improve clinicopathologic correlation.

Discussion

Sub-classification of GGT pathology may be difficult and did not improve clinicopathologic correlation. Better biomarkers of tau pathology are needed.

Globular Glial Mixed Four Repeat Tau and TDP-43 Proteinopathy with Motor Neuron Disease and Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) may be accompanied by frontotemporal dementia (FTD). We report a case of glial mixed tau and TDP-43 proteinopathies in a Japanese patient diagnosed clinically as having ALS-D. Autopsy revealed loss of lower motor neurons and degeneration of the pyramidal tracts in the spinal cord and brain stem. The brain showed frontotemporal lobar degeneration (FTLD), the most severe neuronal loss and gliosis being evident in the precentral gyrus. Although less severe, such changes were also observed in other brain regions, including the basal ganglia and substantia nigra. AT8 immunostaining revealed that predominant occurrence of astrocytic tau lesions termed globular astrocytic inclusions (GAIs) was a feature of the affected regions. These GAIs were Gallyas-Braak negative. Neuronal and oligodendrocytic tau lesions were comparatively scarce. pS409/410 immunostaining also revealed similar neuronal and glial TDP-43 lesions. Interestingly, occasional co-localization of tau and TDP-43 was evident in the GAIs. Immunoblot analyses revealed band patterns characteristic of a 4-repeat (4R) tauopathy, corticobasal degeneration and a TDP-43 proteinopathy, ALS/FTLD-TDP Type B. No mutations were found in the MAPT or TDP-43 genes. We consider that this patient harbored a distinct, sporadic globular glial mixed 4R tau and TDP-43 proteinopathy associated with motor neuron disease and FTD.

A novel tau mutation, p.K317N, causes globular glial tauopathy

Globular glial tauopathies (GGTs) are 4-repeat tauopathies neuropathologically characterized by tau-positive, globular glial inclusions, including both globular oligodendroglial inclusions and globular astrocytic inclusions. No mutations have been found in 25 of the 30 GGT cases reported in the literature who have been screened for mutations in microtubule associated protein tau (MAPT). In this report, six patients with GGT (four with subtype III and two with subtype I) were screened for MAPT mutations. They included 4 men and 2 women with a mean age at death of 73 years (55-83 years) and mean age at symptomatic onset of 66 years (50-77 years). Disease duration ranged from 5 to 14 years. All were homozygous for the MAPT H1 haplotype. Three patients had a positive family history of dementia, and a novel MAPT mutation (c.951G>C, p.K317N) was identified in one of them, a patient with subtype III. Recombinant tau protein bearing the lysine-to-asparagine substitution at amino acid residue 317 was used to assess functional significance of the variant on microtubule assembly and tau filament formation. Recombinant p.K317N tau had reduced ability to promote tubulin polymerization. Recombinant 3R and 4R tau bearing the p.K317N mutation showed decreased 3R tau and increased 4R tau filament assembly. These results strongly suggest that the p.K317N variant is pathogenic. Sequencing of MAPT should be considered in patients with GGT and a family history of dementia or movement disorder. Since several individuals in our series had a positive family history but no MAPT mutation, genetic factors other than MAPT may play a role in disease pathogenesis.

Atypical association of semantic dementia, corticobasal syndrome, and 4R tauopathy

A 57-year-old male with no family history was diagnosed with semantic dementia. He also showed some unusual cognitive features such as episodic memory and executive dysfunctions, spatial disorientation, and dyscalculia. Rapidly progressive cognitive and physical decline occurred. About 1.5 years later, he developed clinical features of a corticobasal syndrome. He died at the age of 60. Brain autopsy revealed numerous 4R-tau-positive lesions in the frontal, parietal and temporal lobes, basal ganglia, and brainstem. Neuronal loss was severe in the temporal cortex. Such association of semantic dementia with tauopathy and corticobasal syndrome is highly unusual. These findings are discussed in the light of current knowledge about frontotemporal lobar degeneration.

Globular glial tauopathies (GGT): consensus recommendations

Recent studies have highlighted a group of 4-repeat (4R) tauopathies that are characterised neuropathologically by widespread, globular glial inclusions (GGIs). Tau immunohistochemistry reveals 4R immunoreactive globular oligodendroglial and astrocytic inclusions and the latter are predominantly negative for Gallyas silver staining. These cases are associated with a range of clinical presentations, which correlate with the severity and distribution of underlying tau pathology and neurodegeneration. Their heterogeneous clinicopathological features combined with their rarity and under-recognition have led to cases characterised by GGIs being described in the literature using various and redundant terminologies. In this report, a group of neuropathologists form a consensus on the terminology and classification of cases with GGIs. After studying microscopic images from previously reported cases with suspected GGIs (n = 22), this panel of neuropathologists with extensive experience in the diagnosis of neurodegenerative diseases and a documented record of previous experience with at least one case with GGIs, agreed that (1) GGIs were present in all the cases reviewed; (2) the morphology of globular astrocytic inclusions was different to tufted astrocytes and finally that (3) the cases represented a number of different neuropathological subtypes. They also agreed that the different morphological subtypes are likely to be part of a spectrum of a distinct disease entity, for which they recommend that the overarching term globular glial tauopathy (GGT) should be used. Type I cases typically present with frontotemporal dementia, which correlates with the fronto-temporal distribution of pathology. Type II cases are characterised by pyramidal features reflecting motor cortex involvement and corticospinal tract degeneration. Type III cases can present with a combination of frontotemporal dementia and motor neuron disease with fronto-temporal cortex, motor cortex and corticospinal tract being severely affected. Extrapyramidal features can be present in Type II and III cases and significant degeneration of the white matter is a feature of all GGT subtypes. Improved detection and classification will be necessary for the establishment of neuropathological and clinical diagnostic research criteria in the future.

Loss of prohibitin membrane scaffolds impairs mitochondrial architecture and leads to tau hyperphosphorylation and neurodegeneration

Fusion and fission of mitochondria maintain the functional integrity of mitochondria and protect against neurodegeneration, but how mitochondrial dysfunctions trigger neuronal loss remains ill-defined. Prohibitins form large ring complexes in the inner membrane that are composed of PHB1 and PHB2 subunits and are thought to function as membrane scaffolds. In Caenorhabditis elegans, prohibitin genes affect aging by moderating fat metabolism and energy production. Knockdown experiments in mammalian cells link the function of prohibitins to membrane fusion, as they were found to stabilize the dynamin-like GTPase OPA1 (optic atrophy 1), which mediates mitochondrial inner membrane fusion and cristae morphogenesis. Mutations in OPA1 are associated with dominant optic atrophy characterized by the progressive loss of retinal ganglion cells, highlighting the importance of OPA1 function in neurons. Here, we show that neuron-specific inactivation of Phb2 in the mouse forebrain causes extensive neurodegeneration associated with behavioral impairments and cognitive deficiencies. We observe early onset tau hyperphosphorylation and filament formation in the hippocampus, demonstrating a direct link between mitochondrial defects and tau pathology. Loss of PHB2 impairs the stability of OPA1, affects mitochondrial ultrastructure, and induces the perinuclear clustering of mitochondria in hippocampal neurons. A destabilization of the mitochondrial genome and respiratory deficiencies manifest in aged neurons only, while the appearance of mitochondrial morphology defects correlates with tau hyperphosphorylation in the absence of PHB2. These results establish an essential role of prohibitin complexes for neuronal survival in vivo and demonstrate that OPA1 stability, mitochondrial fusion, and the maintenance of the mitochondrial genome in neurons depend on these scaffolding proteins. Moreover, our findings establish prohibitin-deficient mice as a novel genetic model for tau pathologies caused by a dysfunction of mitochondria and raise the possibility that tau pathologies are associated with other neurodegenerative disorders caused by deficiencies in mitochondrial dynamics.

Mitochondria are the major site of cellular ATP production and are essential for the survival of neurons. High ATP levels are required to sustain neuronal activities and axonal transport of macromolecules and organelles. The functional integrity of mitochondria depends on fusion and fission of their membranes, which maintain a dynamic mitochondrial network in cells. Interference with these processes causes neurodegenerative disorders that are characterized by axonal degeneration of distinct neurons. However, how an impaired fusion affects mitochondrial activities and neuronal survival remains poorly understood. Here, we have addressed this question by analyzing forebrain-specific knockout mice lacking prohibitins. Prohibitin complexes form membrane scaffolds in the inner membrane, which we now show are required for mitochondrial fusion, ultrastructure, and genome stability in neurons. Loss of prohibitins triggers extensive neurodegeneration associated with behavioral and cognitive deficiencies. Surprisingly, we observe hyperphosphorylation and filament formation of the microtubule-associated protein tau, reminiscent of a large group of neurodegenerative disorders termed tauopathies. Our findings, therefore, not only provide new insight into how defects in mitochondrial fusion affect neuronal survival, but also point to an intimate relationship of deficiencies in mitochondrial dynamics and tau pathologies.

Four-repeat tauopathy clinically presenting as posterior cortical atrophy: atypical corticobasal degeneration?

A man aged 55 with negative family history presented with progressive decline in spatial orientation and visual functions for 2 years. He showed impaired optic fixation, optic ataxia, agraphia, acalculia, ideomotor apraxia, disturbed right-left differentiation but preserved color matching, memory and motor perception, gradually progressing to dementia, without extrapyramidal signs. Brain MRI and PET showed severe bilateral atrophy and hypometabolism in parieto-occipital areas with sparing of visual perception area and frontal lobes. Treatment with cholinesterase inhibitors had no effect. Death occurred 6½ years after onset of symptoms from bronchopneumonia. Clinical diagnosis was posterior cortical atrophy (Benson's syndrome). Autopsy showed severe bilateral parietal cortical atrophy, less severe in other brain regions without subcortical lesions. Histology revealed severe diffuse tauopathy with neuronal loss, neurofibrillary tangles, neuropil threads, and tau deposits in astroglia and oligodendroglia in parietal, temporal, occipital cortex, less in frontal cortex and hippocampus, putamen, claustrum, thalamus and subthalamus. Severely involved white matter showed many tau-positive threads, comma-like inclusions in oligodendroglia (coiled bodies) and in astroglia. Mild neuronal loss in substantia nigra was associated with massive tau pathology, also involving several brainstem nuclei, cerebellum being preserved. There were neither astrocytic plaques nor any amyloid pathology. Neuronal and glial inclusions were generally 4R-tau-positive and 3R-tau-negative. No TDP-43 and α-synuclein inclusions were detected. Spinal cord was not available. No mutations were found in the MAPT gene. This is the first published case with the fully developed clinical and neuroimaging picture of posterior cortical atrophy, morphologically presenting as a distinct phenotype of 4R-tauopathy that closely resembles (atypical) CBD.

Protein coding of neurodegenerative dementias: the neuropathological basis of biomarker diagnostics

Neuropathological diagnosis of neurodegenerative dementias evolved by adapting the results of neuroanatomy, biochemistry, and cellular and molecular biology. Milestone findings of intra- and extracellular argyrophilic structures, visualizing protein deposition, initiated a protein-based classification. Widespread application of immunohistochemical and biochemical investigations revealed that (1) there are modifications of proteins intrinsic to disease (species that are phosphorylated, nitrated, oligomers, proteinase-resistant, with or without amyloid characteristics; cleavage products), (2) disease forms characterized by the accumulation of a single protein only are rather the exception than the rule, and (3) some modifications of proteins elude present neuropathological diagnostic procedures. In this review, we summarize how neuropathology, together with biochemistry, contributes to disease typing, by demonstrating a spectrum of disorders characterized by the deposition of various modifications of various proteins in various locations. Neuropathology may help to elucidate how brain pathologies alter the detectability of proteins in body fluids by upregulation of physiological forms or entrapment of different proteins. Modifications of at least the five most relevant proteins (amyloid-beta, prion protein, tau, alpha-synuclein, and TDP-43), aided by analysis of further "attracted" proteins, are pivotal to be evaluated simultaneously with different methods. This should complement the detection of biomarkers associated with pathogenetic processes, and also neuroimaging and genetic analysis, in order to obtain a highly personalized diagnostic profile. Defining clusters of patients based on the patterns of protein deposition and immunohistochemically or biochemically detectable modifications of proteins ("codes") may have higher prognostic predictive value, may be useful for monitoring therapy, and may open new avenues for research on pathogenesis.

White matter tauopathy with globular glial inclusions: a distinct sporadic frontotemporal lobar degeneration

Frontotemporal lobar degenerations are a group of disorders characterized by circumscribed degeneration of the frontal and temporal lobes and diverse histopathologic features. We report clinical, neuropathologic, ultrastructural, biochemical, and genetic data on 7 individuals with a 4-repeat tauopathy characterized by the presence of globular glial inclusions (GGIs) in brain white matter. Clinical manifestations were compatible with the behavioral variant of frontotemporal dementia and included motor neuron symptoms; there was prominent neuronal loss in the frontal and temporal cortex, subiculum, and amygdala. The surrounding white matter showed abundant GGIs composed of abnormal filaments present mostly in oligodendrocytes. The severity of white matter tau abnormalities correlated with a reduction in myelin and axons and with microglial activation. Western blotting of sarkosyl-insoluble tau demonstrated the presence of 2 major tau bands of 64 and 68 kd. No mutations in the microtubule-associated protein tau gene were detected in 2 affected individuals. We propose that 4-repeat tau-immunoreactive GGIs are the neuropathologic hallmark of a distinct sporadic tauopathy with variable clinical presentations that include frontotemporal dementia and occasionally upper motor neuron disease. This type of tauopathy with GGIs expands the group of neurodegenerativedisorders in which oligodendroglial pathology predominates, beyond the synucleinopathy multiple system atrophy disorders.