Pathological features of FTLD-FUS in a Japanese population: Analyses of nine cases

An autopsy case report of neuronal intermediate filament inclusion disease presenting with predominantly upper motor neuron features

We describe an autopsy case of neuronal intermediate filament inclusion disease (NIFID), a subtype of frontotemporal lobar degeneration (FTLD) with the appearance of fused-in-sarcoma (FUS) inclusions (FTLD-FUS). A 57-year-old man developed dysarthria and dysphagia. One year and five months later, he was admitted to a hospital, and pseudobulbar palsy and right upper motor neuron signs were observed on examination. Needle electromyography revealed no active or chronic denervation. His neurological symptoms gradually deteriorated, and behavioral alterations occurred. He died of hemoperitoneum secondary to rupture of a ureteric tumor. The total duration of the disease was six years and 10 months. Neuropathologically, the frontal cortex, including the motor cortex, and the pyramidal tract were severely affected, whereas the lower motor neurons in the spinal cord and brainstem were mildly damaged. The striatum and substantia nigra were also severely damaged. Hyaline conglomerate inclusions, neuronal cytoplasmic inclusions with a distinct eosinophilic core (so-called cherry spot), Pick body-like inclusions, and eosinophilic round inclusions were observed in the remaining neurons. Immunohistochemical examination revealed that these inclusions were immunoreactive for FUS. HC inclusions were also immunoreactive for α-internexin and phosphorylated neurofilament protein. FUS-immunoreactive NCIs were abundant in the basal ganglia but not in the hippocampus, in contrast to previously reported NIFID cases. Furthermore, Bunina bodies identified by immunohistochemistry for cystatin C were also observed in the lower motor neurons. Bunina bodies may be present in NIFID. This case confirms the pathological heterogeneity of NIFID and supports the notion of the difference between amyotrophic lateral sclerosis and NIFID.

Aberrant interaction between FUS and SFPQ in neurons in a wide range of FTLD spectrum diseases

Fused in sarcoma (FUS) is genetically and clinicopathologically linked to frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). We have previously reported that intranuclear interactions of FUS and splicing factor, proline- and glutamine-rich (SFPQ) contribute to neuronal homeostasis. Disruption of the FUS-SFPQ interaction leads to an increase in the ratio of 4-repeat tau (4R-tau)/3-repeat tau (3R-tau), which manifests in FTLD-like phenotypes in mice. Here, we examined FUS-SFPQ interactions in 142 autopsied individuals with FUS-related ALS/FTLD (ALS/FTLD-FUS), TDP-43-related ALS/FTLD (ALS/FTLD-TDP), progressive supranuclear palsy, corticobasal degeneration, Alzheimer's disease, or Pick's disease as well as controls. Immunofluorescent imaging showed impaired intranuclear co-localization of FUS and SFPQ in neurons of ALS/FTLD-FUS, ALS/FTLD-TDP, progressive supranuclear palsy and corticobasal degeneration cases, but not in Alzheimer's disease or Pick's disease cases. Immunoprecipitation analyses of FUS and SFPQ revealed reduced interactions between the two proteins in ALS/FTLD-TDP and progressive supranuclear palsy cases, but not in those with Alzheimer disease. Furthermore, the ratio of 4R/3R-tau was elevated in cases with ALS/FTLD-TDP and progressive supranuclear palsy, but was largely unaffected in cases with Alzheimer disease. We concluded that impaired interactions between intranuclear FUS and SFPQ and the subsequent increase in the ratio of 4R/3R-tau constitute a common pathogenesis pathway in FTLD spectrum diseases.

Phenotypic variability and its pathological basis in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by its inherent clinicopathological variability. The concurrence of upper and lower motor neuron signs is a common feature in the majority of patients with ALS. However, some patients manifest an atypical clinical course, with only upper or lower motor neuron signs, or various extra-motor symptoms including cognitive dysfunction, parkinsonism, autonomic dysfunction, or ophthalmoparesis. This variability indicates different manifestations of ALS and is reflected by ALS pathology spreading into the central nervous system. The presence of cytoplasmic inclusions positive for transactivation response DNA-binding protein 43 kDa (TDP-43) is a key feature in ALS. Loss of TDP-43 from the nucleus and its subsequent aggregation in the cytoplasm may occur in susceptible regions and may be associated with neuronal loss. However, in some regions, there is no apparent neuronal loss while TDP-43 accumulation is evident; in contrast, in other regions, neuronal loss is apparent without any evidence of TDP-43 accumulation. Therefore, in addition to TDP-43 dysfunction, underlying region-specific cellular vulnerability may exist in the upper and lower motor neurons and frontotemporal system in patients with ALS. The microscopic discrepancy and selective vulnerability may be linked to the macroscopic propensities of the sites of onset, and may also determine the direction and rate of progression of the lesions. Thus, there may be multicentric sites of onset, region-oriented disease development, and different speeds of disease progression across patients with ALS. ALS lesions occur in motor-related areas but may spread to neighboring areas. However, since lesions may spread in a discontinuous manner, and the dynamics of disease propagation have not been able to be identified, it remains controversial whether the stepwise appearance of TDP-43-positive inclusions is based on direct cell-to-cell protein propagation. Further understanding of the phenotypic variability of ALS and its pathological basis may serve as a guide for investigating the underlying pathogenesis of ALS.

Clinical features of the behavioural variant of frontotemporal dementia that are useful for predicting underlying pathological subtypes of frontotemporal lobar degeneration

BACKGROUND

The behavioural variant of frontotemporal dementia (bvFTD) is the most common phenotype of frontotemporal lobar degeneration (FTLD). FTLD is divided into three main pathological subtypes: tau-positive FTLD (FTLD-tau), FTLD-TAR DNA-binding protein (TDP), and FTLD-Fused in sarcoma (FUS). At present, it is difficult to predict the underlying pathological subtypes of sporadic bvFTD before a patient's death.

METHODS

We retrospectively investigated the clinical features of 34 Japanese patients with sporadic bvFTD, with or without motor neuron disease (MND), who had been pathologically diagnosed with FTLD. We examined whether, and how, the clinical features differed among Pick's disease, FTLD-TDP, and FTLD-FUS patients.

RESULTS

Six of the 34 patients developed MND during the course of bvFTD. These six bvFTD-MND patients were all pathologically diagnosed with FTLD-TDP. The other 28 patients were composed of 12 FTLD-tau patients including 11 Pick's disease patients, 8 FTLD-TDP patients, and 8 FTLD-FUS patients. A comparison of the clinical features of the three pathological subtypes of the 33 patients demonstrated that the age at onset was significantly younger in FTLD-FUS patients than in Pick's disease or FTLD-TDP patients. Furthermore, while hyperorality and dietary changes in the early stage of the disease were present in approximately 40% of Pick's disease and FTLD-FUS patients, they were absent in FTLD-TDP patients.

CONCLUSION

The comorbidity of MND, a younger age at onset, and hyperorality and dietary changes in the early stage may be useful clinical features for predicting underlying pathological subtypes of sporadic bvFTD. The results of our study should be confirmed by prospective studies employing a larger number of cases.

Chorea as a clinical feature of the basophilic inclusion body disease subtype of fused-in-sarcoma-associated frontotemporal lobar degeneration

Choreoathetoid involuntary movements are rarely reported in patients with frontotemporal lobar degeneration (FTLD), suggesting their exclusion as a supportive feature in clinical diagnostic criteria for FTLD. Here, we identified three cases of the behavioral variant of frontotemporal dementia (bvFTD) that display chorea with fused in sarcoma (FUS)-positive inclusions (FTLD-FUS) and the basophilic inclusion body disease (BIBD) subtype. We determined the behavioral and cognitive features in this group that were distinct from other FTLD-FUS cases. We also reviewed the clinical records of 72 FTLD cases, and clarified additional clinical features that are predictive of the BIBD pathology. Symptom onset in the three patients with chorea was at 44.0 years of age (±12.0 years), and occurred in the absence of a family history of dementia. The cases were consistent with a clinical form of FTD known as bvFTD, as well as reduced neurological muscle tone in addition to chorea. The three patients showed no or mild parkinsonism, which by contrast, increased substantially in the other FTLD cases until a later stage of disease. The three patients exhibited severe caudate atrophy, which has previously been reported as a histological feature distinguishing FTLD-FUS from FTLD-tau or FTLD-TAR DNA-binding protein 43. Thus, our findings suggest that the clinical feature of choreoathetosis in bvFTD might be associated with FTLD-FUS, and in particular, with the BIBD subtype.