Diffuse thalamic degeneration in fatal familial insomnia. A morphometric study

Neuropathic pain impairs sleep architecture, non-rapid eye movement sleep, and reticular thalamic neuronal activity

BACKGROUND

Neuropathic pain (NP) is a chronic and debilitating condition frequently comorbid with insomnia. However, the alterations in sleep architecture under NP conditions and the mechanisms underlying both pain and sleep disturbances remain poorly understood. The reticular thalamic nucleus (RTN) plays a crucial role in non-rapid eye movement sleep (NREMS) and pain processing, but its involvement in NP-related sleep disruptions has not been fully elucidated.

METHODS

To investigate sleep-related electrophysiological changes in NP, we performed continuous 24-hour electroencephalogram/electromyogram (EEG/EMG) recordings in rats exhibiting allodynia following L5-L6 spinal nerve lesions. Additionally, we assessed the in vivo neuronal activity of the RTN in both NP and sham-operated control rats. Spectral analyses were conducted to examine alterations in sleep oscillatory dynamics. Reticular thalamic nucleus neuronal responses to nociceptive pinch stimuli were classified as increased, decreased, or unresponsive.

RESULTS

Neuropathic pain rats exhibited a significant reduction in NREMS (-20%, P < .001) and an increase in wakefulness (+ 19.13%, P < .05) compared to controls, whereas rapid eye movement sleep (REMS) remained unchanged. Sleep fragmentation was pronounced in NP animals (P < .0001), with frequent brief awakenings, particularly during the inactive/light phase. Spectral analysis revealed increased delta and theta power during both NREMS and REMS. Reticular thalamic nucleus neurons in NP rats displayed a higher basal tonic firing rate, along with increased phasic activity (number of bursts), although the percentage of spikes in bursts remained unchanged.

CONCLUSIONS

Neuropathic pain is characterized by disrupted sleep architecture, reduced NREMS, and heightened RTN neuronal firing activity with partial compensation of burst activity. Given that RTN burst activity is essential for optimal NREMS, its disruption may contribute to NP-induced sleep impairments. These findings suggest that altered EEG/EMG signals, alongside dysregulated RTN neuronal activity, may serve as potential brain markers for NP-related insomnia.

Clinical profile of fatal familial insomnia: phenotypic variation in 129 polymorphisms and geographical regions

OBJECTIVE

Elucidate the core clinical and genetic characteristics and identify the phenotypic variation between different regions and genotypes of fatal familial insomnia (FFI).

METHODS

A worldwide large sample of FFI patients from our case series and literature review diagnosed by genetic testing were collected. The prevalence of clinical symptoms and genetic profile were obtained, and then the phenotypic comparison between Asians versus non-Asians and 129Met/Met versus 129Met/Val were conducted.

RESULTS

In total, 131 cases were identified. The age of onset was 47.51±12.53 (range 17-76) years, 106 patients died and disease duration was 13.20±9.04 (range 2-48) months. Insomnia (87.0%) and rapidly progressive dementia (RPD; 83.2%) occurred with the highest frequency. Hypertension (33.6%) was considered to be an objective indicator of autonomic dysfunction. Genotype frequency at codon 129 was Met/Met (84.7%) and Met/Val (15.3%), and allele frequency was Met (92.4%) and Val (7.6%).129 Met was a risk factor (OR: 3.728, 95% CI: 2.194 to 6.333, p=0.000) for FFI in the non-Asian population. Comparison of Asians and non-Asians revealed clinical symptoms and genetic background to show some differences (p<0.05). In the comparison of 129 polymorphisms, a longer disease duration was found in the 129 MV group, with alleviation of some clinical symptoms (p<0.05). After considering survival probability, significant differences in survival time between genotypes remained (p<0.0001).

CONCLUSIONS

Insomnia, RPD and hypertension are representative key clinical presentations of FFI. Phenotypic variations in genotypes and geographic regions were documented. Prion protein gene 129 Met was considered to be a risk factor for FFI in the non-Asian population, and 129 polymorphisms could modify survival duration.

PMCA-generated prions from the olfactory mucosa of patients with Fatal Familial Insomnia cause prion disease in mice

Background:

Fatal Familial Insomnia (FFI) is a genetic prion disease caused by the D178N mutation in the prion protein gene (PRNP) in coupling phase with methionine at PRNP 129. In 2017, we have shown that the olfactory mucosa (OM) collected from FFI patients contained traces of PrPSc detectable by Protein Misfolding Cyclic Amplification (PMCA).

Methods:

In this work, we have challenged PMCA-generated products obtained from OM and brain homogenate of FFI patients in BvPrP-Tg407 transgenic mice expressing the bank vole prion protein to test their ability to induce prion pathology.

Results:

All inoculated mice developed mild spongiform changes, astroglial activation, and PrPSc deposition mainly affecting the thalamus. However, their neuropathological alterations were different from those found in the brain of BvPrP-Tg407 mice injected with raw FFI brain homogenate.

Conclusions:

Although with some experimental constraints, we show that PrPSc present in OM of FFI patients is potentially infectious.

Funding:

This work was supported in part by the Italian Ministry of Health (GR-2013-02355724 and Ricerca Corrente), MJFF, ALZ, Alzheimer’s Research UK and the Weston Brain Institute (BAND2015), and Euronanomed III (SPEEDY) to FM; by the Spanish Ministerio de Economía y Competitividad (grant AGL2016-78054-R [AEI/FEDER, UE]) to JMT and JCE; AM-M was supported by a fellowship from the INIA (FPI-SGIT-2015-02).

Clinical features and genetic characteristics of two Chinese pedigrees with fatal family insomnia

Background: Fatal familial insomnia (FFI) is a rare autosomal-dominant inherited prion disease characterized clinically by severe sleep disorder, motor signs, dysautonomia and abnormal behaviour. FFI is caused by a missense mutation at codon 178 of the prion protein gene (PRNP). Our study is aimed to explore typical clinical and genetic features of two Chinese pedigrees with FFI and review the related literatures.

Methods: Two FFI cases with family histories were recruited in our study. The main clinical features, genetic features and possible pathophysiologic mechanisms of these two FFI cases were analysed.

Results: The foremost symptoms seemed to be sleep disturbances and psychosis. Progressive sympathetic symptoms, movement disturbances and memory loss were frequently observed as well. Electroencephalography (EEG) showed a minor slowing without periodic triphasic waves. Polysomnography (PSG) showed reduction in total sleep time and disturbance of sleep-related respiratory. Brain magnetic resonance imaging (MRI) did not reveal obvious abnormality. Genetic analysis disclosed the prion protein gene mutation at codon 178 (D178N), with methionine (Met) homozygosity at the polymorphic position 129 (Met129Met).

Conclusions: The major clinical features of Chinese FFI are sleep dysfunction, psychiatric symptoms and sympathetic symptoms. Our patients have similar clinical characteristics as that of the typical FFI cases.

Clinical Features and Sleep Analysis of Chinese Patients with Fatal Familial Insomnia

This study aimed to examine clinical features, sleep, abnormal sleep-wake transition and non-sleep disturbances as well as lab tests in Chinese fatal familial insomnia (FFI) subjects. Patients with confirmed clinical and laboratory diagnosis of FFI have been retrospectively reviewed. The clinical features and the results of the complementary tests, including polysomnography (PSG), brain imaging and genetic analysis, were used. Two male and three female patients were recruited in this study. Three of the five patients had more comprehensive family medical records. The most typical clinical manifestations in all 5 patients were sleep disturbances, including insomnia, laryngeal stridor, sleep breath disturbance, and sleep-related involuntary movements. PSG of all these five cases showed reduction in total sleep time, sleep fragmentation, abnormal short non-rapid eye movement - rapid eye movement (REM) cycling, REM sleep reduction or loss, and REM sleep instruction in wakefulness. Patient 2's emission tomography scan demonstrated a reduction in glucose uptake in the left thalamus and bilateral inferior parietal lobe. In summary, Chinese FFI patients are typically characterized by organic sleep related symptoms, rapidly progressive dementia and sympathetic symptoms. We propose that structural damages in the thalamus and cortex are mostly responsible for clinical manifestations of FFI.

Transgenic fatal familial insomnia mice indicate prion infectivity-independent mechanisms of pathogenesis and phenotypic expression of disease

Fatal familial insomnia (FFI) and a genetic form of Creutzfeldt-Jakob disease (CJD¹⁷⁸) are clinically different prion disorders linked to the D178N prion protein (PrP) mutation. The disease phenotype is determined by the 129 M/V polymorphism on the mutant allele, which is thought to influence D178N PrP misfolding, leading to the formation of distinctive prion strains with specific neurotoxic properties. However, the mechanism by which misfolded variants of mutant PrP cause different diseases is not known. We generated transgenic (Tg) mice expressing the mouse PrP homolog of the FFI mutation. These mice synthesize a misfolded form of mutant PrP in their brains and develop a neurological illness with severe sleep disruption, highly reminiscent of FFI and different from that of analogously generated Tg(CJD) mice modeling CJD¹⁷⁸. No prion infectivity was detectable in Tg(FFI) and Tg(CJD) brains by bioassay or protein misfolding cyclic amplification, indicating that mutant PrP has disease-encoding properties that do not depend on its ability to propagate its misfolded conformation. Tg(FFI) and Tg(CJD) neurons have different patterns of intracellular PrP accumulation associated with distinct morphological abnormalities of the endoplasmic reticulum and Golgi, suggesting that mutation-specific alterations of secretory transport may contribute to the disease phenotype.

Genetic prion diseases are degenerative brain disorders caused by mutations in the gene encoding the prion protein (PrP). Different PrP mutations cause different diseases, including Creutzfeldt-Jakob disease (CJD) and fatal familial insomnia (FFI). The reason for this variability is not known, but assembly of the mutant PrPs into distinct aggregates that spread in the brain by promoting PrP aggregation may contribute to the disease phenotype. We previously generated transgenic mice modeling genetic CJD, clinically identified by dementia and motor abnormalities. We have now generated transgenic mice carrying the PrP mutation associated with FFI, and found that they develop severe sleep abnormalities and other key features of the human disorder. Thus, transgenic mice recapitulate the phenotypic differences seen in humans. The mutant PrPs in FFI and CJD mice are aggregated but unable to promote PrP aggregation. They accumulate in different intracellular compartments and cause distinct morphological abnormalities of transport organelles. These results indicate that mutant PrP has disease-encoding properties that are independent of its ability to self-propagate, and suggest that the phenotypic heterogeneity may be due to different effects of aggregated PrP on intracellular transport. Our study provides new insights into the mechanisms of selective neuronal dysfunction due to protein aggregation.

Thalamo-striatal diffusion reductions precede disease onset in prion mutation carriers

Human prion diseases present substantial scientific and public health challenges. They are unique in being sporadic, infectious and inherited, and their pathogen is distinct from all other pathogens in lacking nucleic acids. Despite progress in understanding the molecular structure of prions, their initial cerebral pathophysiology and the loci of cerebral injury are poorly understood. As part of a large prospective study, we analysed early diffusion MRI scans of 14 patients with the E200K genetic form of Creutzfeldt-Jakob Disease, 20 healthy carriers of this mutation that causes the disease and 20 controls without the mutation from the same families. Cerebral diffusion was quantified by the Apparent Diffusion Coefficient, and analysed by voxel-wise statistical parametric mapping technique. Compared to the mutation-negative controls, diffusion was significantly reduced in a thalamic-striatal network, comprising the putamen and mediodorsal, ventrolateral and pulvinar thalamic nuclei, in both the patients and the healthy mutation carriers. With disease onset, these diffusion reductions intensified, but did not spread to other areas. The caudate nucleus was reduced only after symptomatic onset. These findings indicate that cerebral diffusion reductions can be detected early in the course of Creutzfeldt-Jakob Disease, and years before symptomatic onset in mutation carriers, in a distinct subcortical network. We suggest that this network is centrally involved in the pathogenesis of Creutzfeldt-Jakob Disease, and its anatomical connections are sufficient to account for the common symptoms of this disease. Further, we suggest that the abnormalities in healthy mutation-carrying subjects may reflect the accumulation of abnormal prion protein and/or associated vacuolation at this time, temporally close to disease onset.

Changes in neuropeptide expression in mice infected with prions

Prion diseases are neurodegenerative disorders characterized by accumulation of an aberrantly folded isoform (PrP(Sc)) of the normal prion protein (PrP(C)). Using in situ hybridization and immunohistochemistry, we have studied changes in the expression of neuropeptides, acetylcholinesterase and tyrosine hydroxylase in CD1 and FVB wild-type mouse strains, as well as in PrP(C) null mice and in mice overexpressing PrP(C) following intracerebral inoculation with RML or Me7 prions. In the immunohistochemical analysis, neuropeptide Y (NPY), enkephalin and dynorphin-like immunoreactivities increased in mossy fibers of CD1 and FVB mice inoculated with either RML- or Me7 prions, whereas cholecystokinin-like immunoreactivity was decreased. These changes in peptide levels were paralleled by an increase in the transcripts in granule cells for neuropeptide Y, enkephalin, and cholecystokinin. However, the dynorphin transcript was decreased in the granule cells. The changes occurred more rapidly in PrP(C)-overexpressing compared to wild-type mice, and could not be found at all in PrP(C)-knockout mice. These changes in peptide expression, which mostly occur before appearance of symptoms of disease, may reflect attempts to initiate protective and/or regenerative processes.

Fatal familial insomnia: a model disease in sleep physiopathology

Fatal Familial Insomnia (FFI) is characterized by loss of sleep, oneiric stupor with autonomic/motor hyperactivity and somato-motor abnormalities (pyramidal signs, myoclonus, dysarthria/dysphagia, ataxia). Positon emission tomography (PET) disclosed thalamic hypometabolism and milder involvement of the cortex; neuropathology severe neuronal loss in the thalamic nuclei variably affecting the caudate, gyrus cinguli and fronto-temporal cortices. Genetic analysis disclosed a mutation in the PRNP gene and FFI was transmitted to experimental animals, thus classifying FFI within the prion diseases. Rare Sporadic Fatal Insomnia (SFI) cases occur without PRNP mutation but with features similar to FFI. FFI represents a model disease for the study of sleep-wake regulation: (I) the profound thalamic hypometabolism/atrophy associated with lack of sleep spindles and delta sleep implicate the thalamus in the origin of slow wave sleep (SWS); (II) loss of SWS is associated with marked autonomic and motor hyperactivity; termed 'agrypnia excitata', this association has been proposed as a useful clinical concept representative of thalamo-limbic dysfunction; (III) lack of SWS occurs with substantial preservation of stage 1 NREM sleep, implying that the latter has mechanisms different from SWS and unaffected by thalamic atrophy; accordingly, conflating stage 1 NREM with SWS into NREM sleep is inappropriate.

Familial and sporadic fatal insomnia

Familial fatal insomnia (FFI)--a hereditary prion disease caused by a mutation at codon 178 of the prion-protein (PrP) gene (PRNP) that leads to a D178N substitution in the protein--and its sporadic form, sporadic fatal insomnia (SFI), have similar disease phenotypes. Both disorders have clinical features of disrupted sleep (loss of sleep spindles and slow-wave sleep and enacted dreams during rapid-eye-movement sleep), autonomic hyperactivation, and motor abnormalities (myoclonus, ataxia, dysarthria, dysphagia, and pyramidal signs). PET shows pronounced thalamic and limbic hypometabolism that becomes more widespread in later stages. Neuropathological assessment reveals severe neuronal loss and astrogliosis of the anterior medial thalamus and inferior olives, with later cerebral cortical and cerebellar involvement. Accumulation of an isoform of protease-resistant PrP fragment in FFI distinct from that found in a familial form of Creutzfeldt-Jakob disease with the same D178N mutation, shows the effect of the polymorphism at codon 129 of PRNP on phenotypic expression and the possibility of distinct prion "strains" with diverse pathological potential. Intriguing clinicopathological correlations in FFI and SFI suggest a role for the thalamolimbic system in the regulation of sleep and other circadian functions.

Subacute diencephalic angioencephalopathy: biopsy diagnosis and radiological features of a rare entity

Subacute diencephalic angioencephalopathy (SDAE) is a rare and fatal disease of unknown etiology that involves the thalami bilaterally. To date, there have been four cases reported, in which the diagnosis was established only after post mortem examination of the brain. We report two male patients, ages 69 and 41 years, who presented with progressive dementia and somnolence. Radiological evaluation revealed enhancing lesions involving both thalami. The differential diagnosis included a number of neoplastic, inflammatory and vascular processes. In both cases, pathological evaluation of biopsy specimens suggested the diagnosis of SDAE. Despite supportive care, the disease progressed rapidly and both patients died within weeks after initial presentation. The diagnosis was confirmed at autopsy in both cases. SDAE is a rare cause of bithalamic disease that can be mistaken for a neoplasm as well as a number of conditions that necessitate different treatment choices. The histopathological findings can establish the diagnosis when combined with radiological and clinical information. This report emphasizes the utility of stereotactic biopsy in early diagnosis of SDAE.