Transthyretin-type cerebral amyloid angiopathy in type I familial amyloid polyneuropathy

Brain MRI in patients with V30M hereditary transthyretin amyloidosis

BACKGROUND

Central nervous system dysfunction is common in longstanding hereditary transthyretin amyloidosis (ATTRv) caused by the V30M (p.V50M) mutation. Neuropathology studies show leptomeningeal amyloid deposition and cerebral amyloid angiopathy (CAA). Brain MRI is widely used in the assessment of Aβ associated CAA but there are no systematic studies with brain MRI in ATTRv amyloidosis.

METHODS

we performed 3 T brain MRIs in 16 patients with longstanding (>14 years) ATTRV30M. We additionally retrospectively reviewed 48 brain MRIs from patients followed at our clinic. CNS symptoms and signs were systematically accessed, and MRIs were blindly reviewed for ischaemic and haemorrhagic lesions.

RESULTS

in the prospective cohort, we found white matter hyperintensities in 8/16 patients (50%, Fazekas score> =1). There were no relevant microbleeds, large ischaemic or haemorrhagic lesions or superficial siderosis. In the retrospective cohort, microbleeds were found in 5/48 patients (10,4%), two of which with > =20 microbleeds. White matter hyperintensities were found in 20/48 cases (41.7%). White matter lesions, microbleeds and cortical atrophy were not associated with disease duration.

CONCLUSIONS

white matter hyperintensities are common in ATTRV30M, irrespective of disease duration. Haemorrhagic lesions are rare, even in patients with longstanding disease, suggesting the existence of other risk factors.

Tafamidis concentration required for transthyretin stabilisation in cerebrospinal fluid

BACKGROUND

Hereditary transthyretin (TTR) amyloidosis (ATTRv) initially presents as a polyneuropathy and/or a cardiomyopathy. Central nervous system (CNS) pathology in ATTRv amyloidosis, including focal neurological episodes, dementia, cerebrovascular bleeding, and seizures, appears around a decade later. Wild-type (WT) TTR amyloidosis (ATTRwt) causes a cardiomyopathy. CNS pathology risk likely also increases in these patients as cardiomyopathy progresses. Herein, we study tafamidis-mediated TTR kinetic stabilisation in cerebrospinal fluid (CSF).

METHODS

Varying tafamidis concentrations (50-1000 nM) were added to CSF from healthy donors or ATTRv patients, and TTR stabilisation was measured via the decrease in dissociation rate.

RESULTS

Tafamidis meglumine (Vyndaqel) can be dosed at 20 or 80 mg QD. The latter dose is bioequivalent to a 61 mg QD dose of tafamidis free acid (Vyndamax). The tafamidis CSF concentration in ATTRv patients on 20 mg Vyndaqel is ∼125 nM. By linear extrapolation, we expect a CSF concentration of ∼500 nM at the higher dose. When tafamidis is added to healthy donor CSF at 125 or 500 nM, the WT TTR dissociation rate decreases by 42% or 87%, respectively.

CONCLUSIONS

Tafamidis stabilises TTR in CSF to what is likely a clinically meaningful extent at CSF concentrations achieved by the normal tafamidis dosing regimen.

Neuropathology of central nervous system involvement in TTR amyloidosis

Hereditary transthyretin amyloidosis (ATTRv) is a systemic disease caused by the accumulation of misfolded transthyretin (TTR). It usually presents with an adult-onset progressive axonal peripheral neuropathy and cardiomyopathy. In the central nervous system (CNS), variant TTR is produced by the choroid plexus and accumulates in the leptomeninges. CNS symptoms have been increasingly recognized in this population, including transient focal neurological episodes and stroke, particularly in patients with the V30M mutation and longstanding disease. The prevalence, pathophysiology, and progression of CNS involvement remain to be clarified. The present work explores if there is a recognizable sequence of CNS TTR deposition in ATTRv. We studied the topographical and severity distribution of TTR deposition in 16 patients with ATTRv, aged 27-69 years and with a mean disease duration of 10.9 years (range: 3-29). Our results suggest that CNS pathological involvement in V30M ATTRv occurs early in the disease course, probably starting in pre-symptomatic phases, and follows a distinct sequence. Leptomeninges and subarachnoid meningeal vessels are affected earlier, then followed by perforating cortical vessels and subpial deposition, and finally by deposition in the subependymal and basal ganglia vessels near the ependymal lining. Brainstem and spinal cord show early and severe involvement, with amyloid subpial deposition already seen in initial stages. Despite massive superficial amyloid deposition, no parenchymal deposition outside subpial or subependymal regions was found. Additionally, vascular lesions or superficial cortical siderosis were not frequent. Future studies with more patients from different populations and TTR mutations will be important to confirm these findings. Defining stages of TTR pathology in the CNS may be useful to better understand pathogenic mechanisms leading to symptoms and to interpret neuroimaging biomarkers.

A case of transthyretin-related cerebral amyloid angiopathy. The other side of hereditary transthyretin amyloidosis

The target organs for familial transthyretin amyloidosis are typically the nerves, the heart or even the eyes due to the accumulation of amyloid deposits. Less frequently, these deposits can occur within the central nervous system and drive a specific phenotype of cerebral amyloid angiopathy. We report the case of a 72-year-old woman showing evidence of cerebral amyloid angiopathy, in a context of hereditary transthyretin amyloidosis (hATTR) due to p.(Ser77Tyr) mutation of the TTR gene. Her cognitive assessment on a two-year follow-up was remarkably steady. A very limited number of patients with hereditary transthyretin amyloidosis associated with a cerebral amyloid angiopathy have been reported. Few characteristics could distinguish them from classic cerebral amyloid angiopathy, and more data are needed to highlight specific features. Screening for peripheral neuropathy should be considered for patients referred to memory clinic for atypical cerebral amyloid angiopathy.

Are we creating a new phenotype? Physiological barriers and ethical considerations in the treatment of hereditary transthyretin-amyloidosis

Hereditary transthyretin (TTR) amyloidosis (ATTRv) is an autosomal dominant, systemic disease transmitted by amyloidogenic mutations in the TTR gene. To prevent the otherwise fatal disease course, TTR stabilizers and mRNA silencing antisense drugs are currently approved treatment options. With 90% of the amyloidogenic protein produced by the liver, disease progression including polyneuropathy and cardiomyopathy, the two most prominent manifestations, can successfully be halted by hepatic drug targeting or-formerly-liver transplantation. Certain TTR variants, however, favor disease manifestations in the central nervous system (CNS) or eyes, which is mostly associated with TTR production in the choroid plexus and retina. These compartments cannot be sufficiently reached by any of the approved medications. From liver-transplanted patients, we have learned that with longer lifespans, such CNS manifestations become more relevant over time, even if the underlying TTR mutation is not primarily associated with such. Are we therefore creating a new phenotype? Prolonging life will most likely lead to a shift in the phenotypic spectrum, enabling manifestations like blindness, dementia, and cerebral hemorrhage to come out of the disease background. To overcome the first therapeutic limitation, the blood-brain barrier, we might be able to learn from other antisense drugs currently being used in research or even being approved for primary neurodegenerative CNS diseases like spinal muscular atrophy or Alzheimer's disease. But what effects will unselective CNS TTR knock-down have considering its role in neuroprotection? A potential approach to overcome this second limitiation might be allele-specific targeting, which is, however, still far from clinical trials. Ethical standpoints underline the need for seamless data collection to enable more evidence-based decisions and for thoughtful consenting in research and clinical practice. We conclude that the current advances in treating ATTRv amyloidosis have become a meaningful example for mechanism-based treatment. With its great success in improving patient life spans, we will still have to face new challenges including shifts in the phenotype spectrum and the ongoing need for improved treatment precision. Further investigation is needed to address these closed barriers and open questions.

CNS Involvement in Hereditary Transthyretin Amyloidosis

Hereditary transthyretin amyloidosis (ATTRv amyloidosis) is predominantly a disease of the peripheral nerves, heart, kidney and eye. CNS involvement has been a marginal issue in research and the clinical setting, until recently. Growing evidence shows that leptomeningeal amyloid accumulation is frequent and present from early stages of ATTRv amyloidosis. Several recent studies show CNS symptoms arise as a common late complication in patients with the V30M mutation, after at least 14 years of symptomatic peripheral nerve disease. Conversely, in non-V30M patients, there are several descriptions, mostly case reports, of patients presenting with severe phenotypes of ocular and CNS dysfunction (oculoleptomeningeal amyloidosis), with little systemic involvement. This phenotype is found in rare families worldwide, associated with at least 14 mutations.In both patients with late and early onset CNS dysfunction, symptoms include transient focal neurological episodes, haemorrhagic and ischemic stroke, cognitive decline and cranial nerve dysfunction. Pathologically, there is severe amyloid deposition in the leptomeninges and cerebral amyloid angiopathy of leptomeningeal and penetrating vessels. These amyloid aggregates are formed mostly by CSF produced TTR and seem resistant to the available ATTRv therapies that increase the stability or reduce the production of plasma TTR. This indicates that CNS involvement will become a meaningful issue in patient management in upcoming years.

Transthyretin amyloid-related transitory events (TARTEs): Descriptive analysis of clinical, imagiological, and neurophysiological features

Transthyretin-related familial amyloid polyneuropathy (ATTR-FAP) is a multisystemic disorder inherited as an autosomal dominant trait. Transitory events in ATTR-FAP patients are a feature of this disorder and remain poorly depicted in the literature. We aimed to describe a case series of ATTR-FAP patients who presented to our department with transitory events and document the clinical, neuroimaging and neurophysiological characteristics of the events. We collected data from eight patients carrying the Val30Met ATTR-FAP variant. We registered a total of 23 events. Of the eight patients, seven had been submitted to hepatic transplant. The events were either TIA-like or seizures, often followed by prolonged language, motor or sensory impairment. In 9 (39%) of the events, the patients presented with fever, but an infection was only found in 5 (21%). Cerebrospinal fluid analysis was performed in 5 patients. EEG was abnormal in at least 1 event in 7 of the 8 patients. Brain MRI was performed in 3 patients during the acute stage and showed no acute lesions. Although the etiology of these events remains unclear, brain MRI performed in the acute phase of acute TIA-like events and the EEG abnormalities, argues in favor of regional brain dysfunction due to amyloid deposition. Focal neurological episodes should be considered in long-term duration Val30Met ATTR-FAP patients, who present with acute neurological deficits or seizures.

Transthyretin interacts with actin regulators in a Drosophila model of familial amyloid polyneuropathy

Familial amyloid polyneuropathy (FAP) is a neurodegenerative disorder whose major hallmark is the deposition of mutated transthyretin (TTR) in the form of amyloid fibrils in the peripheral nervous system (PNS). The exposure of PNS axons to extracellular TTR deposits leads to an axonopathy that culminates in neuronal death. However, the molecular mechanisms underlying TTR-induced neurodegeneration are still unclear, despite the extensive studies in vertebrate models. In this work we used a Drosophila FAP model, based on the expression of the amyloidogenic TTR (V30M) in the fly retina, to uncover genetic interactions with cytoskeleton regulators. We show that TTR interacts with actin regulators and induces cytoskeleton alterations, leading to axonal defects. Moreover, our study pinpoints an interaction between TTRV30M and members of Rho GTPase signaling pathways, the major actin regulators. Based on these findings we propose that actin cytoskeleton alterations may mediate the axonopathy observed in FAP patients, and highlight a molecular pathway, mediated by Rho GTPases, underlying TTR-induced neurodegeneration. We expect this work to prompt novel studies and approaches towards FAP therapy.

The frequency of central nervous system complications in the Cypriot cohort of ATTRV30M neuropathy transplanted patients

BACKGROUND

Hereditary transthyretin amyloidosis (ATTR) is a hereditary, sensorimotor and autonomic neuropathy caused by deposits of mutated transthyretin (TTR). The commonest TTR mutation is V30M (ATTRV30M) with patients usually living for about 10 years after disease onset. Liver transplantation (LT) until recently was considered the standard treatment.

OBJECTIVE AND METHODS

This study aims to assess the frequency of CNS complications in post-LT patients from the Cypriot cohort. Epidemiological data were collected for all genetically confirmed ATTRV30M neuropathy patients diagnosed at CING since 1992, and CNS-associated symptoms were assessed and evaluated by two neurology specialists.

RESULTS

Out of the 48 transplanted patients, 10 (20.8%) presented with a CNS complication. All patients had ocular involvement, mainly glaucoma (7/10). Eight presented with transient focal neurological episodes (TFNEs), with expressive dysphasia being reported by four of them. The mean time of TFNE-emergence was 16.6 years after the LT. Three died from cerebral hemorrhage.

CONCLUSIONS

CNS complications in post-LT ATTRV30M patients are not rare and usually manifest themselves at a time that surpasses the mean time the patients would have survived without a LT. CNS involvement is associated with increased mortality, due to cerebral hemorrhage.

Current and future treatment of amyloid diseases

There are more than 30 human proteins whose aggregation appears to cause degenerative maladies referred to as amyloid diseases or amyloidoses. These disorders are named after the characteristic cross-β-sheet amyloid fibrils that accumulate systemically or are localized to specific organs. In most cases, current treatment is limited to symptomatic approaches and thus disease-modifying therapies are needed. Alzheimer's disease is a neurodegenerative disorder with extracellular amyloid β-peptide (Aβ) fibrils and intracellular tau neurofibrillary tangles as pathological hallmarks. Numerous clinical trials have been conducted with passive and active immunotherapy, and small molecules to inhibit Aβ formation and aggregation or to enhance Aβ clearance; so far such clinical trials have been unsuccessful. Novel strategies are therefore required and here we will discuss the possibility of utilizing the chaperone BRICHOS to prevent Aβ aggregation and toxicity. Type 2 diabetes mellitus is symptomatically treated with insulin. However, the underlying pathology is linked to the aggregation and progressive accumulation of islet amyloid polypeptide as fibrils and oligomers, which are cytotoxic. Several compounds have been shown to inhibit islet amyloid aggregation and cytotoxicity in vitro. Future animal studies and clinical trials have to be conducted to determine their efficacy in vivo. The transthyretin (TTR) amyloidoses are a group of systemic degenerative diseases compromising multiple organ systems, caused by TTR aggregation. Liver transplantation decreases the generation of misfolded TTR and improves the quality of life for a subgroup of this patient population. Compounds that stabilize the natively folded, nonamyloidogenic, tetrameric conformation of TTR have been developed and the drug tafamidis is available as a promising treatment.

Cerebral amyloid angiopathy in posttransplant patients with hereditary ATTR amyloidosis

OBJECTIVE

To investigate the prevalence and clinical features of posttransplant CNS symptoms in patients with hereditary ATTR amyloidosis and their Pittsburgh compound B (PiB)-PET imaging correlates.

METHODS

We monitored prevalence and type of CNS symptoms in 53 consecutive posttransplant patients with hereditary ATTR amyloidosis. (11)C-PiB-PET was performed in 15 patients with various disease durations. We also analyzed pathologic and biochemical characteristics of ATTR amyloid deposition in the brain of a posttransplant patient.

RESULTS

Transient focal neurologic episodes (TFNEs) attributed to ATTR-type cerebral amyloid angiopathy (CAA) were found in 11.3% of posttransplant hereditary ATTR amyloidosis patients. TFNE occurred on average 16.8 years after onset of the disease. Patients with longer duration of illness (≥10 years) showed increased (11)C-PiB retention in the brain. The (11)C-PiB accumulation pattern in hereditary ATTR amyloidosis was unique and different from those in Alzheimer disease or Aβ-type CAA. In the autopsy case, ATTR amyloid deposition was mainly localized to leptomeningeal vessels and leptomeninges of the brain. Amyloid fibrils in the brain were almost completely composed of variant transthyretin (TTR).

CONCLUSIONS

TFNE due to ATTR-type CAA occurred frequently in posttransplant patients with long disease durations. (11)C-PiB-PET is a useful diagnostic tool for ATTR-type CAA. ATTR amyloid deposition in the CNS, as measured by PiB-PET, was detected approximately 10 years before onset of TFNE.

[Familial amyloid polyneuropathy involving a homozygous Val30Met mutation in the amyloidogenic transthyretin gene presenting with superficial siderosis: a case report]

A 76-year-old woman was admitted to our hospital because of transthyretin-related familial amyloid polyneuropathy (TTR-FAP). She had developed bilateral vitreous opacity at the age of 58 and paroxysmal atrial fibrillation at the age of 62. She suffered gait disturbance and dysesthesia of the limbs at the age of 68 and was diagnosed with FAP involving a homozygous Val30Met mutation in the amyloidogenic transthyretin (ATTR) gene after a genetic test. Her parents were cousins, and her aunt's medical history included pacemaker implantation and polyneuropathy. At the age of 74, the patient developed gait disturbance and dysesthesia of her extremities. A neurological examination revealed visual loss, hearing impairment, distal muscle weakness, dysesthesia, and decreased sensation in all modalities in her extremities. She could neither walk nor remain standing without support. Brain magnetic resonance imaging (MRI) revealed a low intensity lesion on the surface of the cerebellum on T2*-weighted images and susceptibility-weighted images. A low intensity pattern that was indicative of the classical type of superficial siderosis was detected. At the age of 76, when she was admitted to our hospital because of the deterioration of her gait disturbance and dysesthesia, brain MRI showed that the patient's cerebellar atrophy and hemosiderin deposition had worsened. Some reports suggest that FAP patients that are homozygous for the ATTR Val30Met mutation are more likely to develop central nervous involvement than those that are heterozygous for the mutation. Superficial siderosis may be responsible for the central nervous involvement.

Neuropathologic analysis of Tyr69His TTR variant meningovascular amyloidosis with dementia

Transthyretin/TTR gene mutations usually cause systemic amyloidotic diseases. Few TTR variants preferentially affect the central nervous system, manifesting as oculoleptomeningeal amyloidosis. Patients with TTR meningovascular amyloidosis often show dementia, however the neuropathologic features of dementia in these cases have not been elucidated. We report the neuropathologic findings from a brain autopsy of a 72-year-old man with the rare Tyr69His (Y69H) TTR gene variant, dementia and ataxia. Severe amyloid deposits were observed in the leptomeninges and in a subpial and subependymal distribution. Mass spectrometry analysis demonstrated that the amyloid deposits were comprised of over 80 % of the variant TTR. TTR was undetectable by mass spectrometry in the neocortex subjacent to the subpial amyloid deposits. Subpial TTR amyloid deposits were associated with brisk superficial reactive gliosis and siderosis in the neocortex and cerebellar cortex. Subependymal TTR amyloid deposits were associated with subjacent myelin pallor in the hippocampal outflow tract structures including the alveus, fimbria and fornix. Phospho-tau immunostains demonstrated transentorhinal-stage neurofibrillary degeneration (Braak stage II) which, in the absence of neocortical amyloid-beta and neuritic plaques, was indicative of primary age-related tauopathy (PART). However, distinctive phospho-tau aggregates were observed subjacent to the subpial TTR amyloid deposits in all regions of the neocortex, including the primary motor and striate cortices, suggesting a potential link between TTR amyloid and neocortical tauopathy. Our report reveals novel insights into the potential neuropathologic substrates of dementia in variant TTR amyloidosis that need to be investigated in larger autopsy series.

CNS involvement in V30M transthyretin amyloidosis: clinical, neuropathological and biochemical findings

OBJECTIVES

Since liver transplant (LT) was introduced to treat patients with familial amyloid polyneuropathy carrying the V30M mutation (ATTR-V30M), ocular and cardiac complications have developed. Long-term central nervous system (CNS) involvement was not investigated. Our goals were to: (1) identify and characterise focal neurological episodes (FNEs) due to CNS dysfunction in ATTR-V30M patients; (2) characterise neuropathological features and temporal profile of CNS transthyretin amyloidosis.

METHODS

We monitored the presence and type of FNEs in 87 consecutive ATTR-V30M and 35 non-ATTR LT patients. FNEs were investigated with CT scan, EEG and extensive neurovascular workup. MRI studies were not performed because all patients had cardiac pacemakers as part of the LT protocol. We characterised transthyretin amyloid deposition in the brains of seven ATTR-V30M patients, dead 3-13 years after polyneuropathy onset.

RESULTS

FNEs occurred in 31% (27/87) of ATTR-V30M and in 5.7% (2/35) of the non-ATTR transplanted patients (OR=7.0, 95% CI 1.5 to 33.5). FNEs occurred on average 14.6 years after disease onset (95% CI 13.3 to 16.0) in ATTR-V30M patients, which is beyond the life expectancy of non-transplanted ATTR-V30M patients (10.9, 95% CI 10.5 to 11.3). ATTR-V30M patients with FNEs had longer disease duration (OR=1.24; 95% CI 1.07 to 1.43), renal dysfunction (OR=4.65; 95% CI 1.20 to 18.05) and were men (OR=3.57; 95% CI 1.02 to 12.30). CNS transthyretin amyloidosis was already present 3 years after polyneuropathy onset and progressed from the meninges and its vessels towards meningocortical vessels and the superficial brain parenchyma, as disease duration increased.

CONCLUSIONS

Our findings indicate that CNS clinical involvement occurs in ATTR-V30M patients regardless of LT. Longer disease duration after LT can provide the necessary time for transthyretin amyloidosis to progress until it becomes clinically relevant. Highly sensitive imaging methods are needed to identify and monitor brain ATTR. Disease modifying therapies should consider brain TTR as a target.

Transthyretin-related familial amyloidotic polyneuropathy-Progress in Kumamoto, Japan (1967-2010)-

The authors reviewed contribution of Kumamoto University group to the progress of the studies on transthyretin (TTR)-related familial amyloidotic polyneuropathy (TTR-related FAP) for 42 years (from 1967 to 2009). Andrade (1952) first described a large group of patients with FAP in Portugal and Araki et al. (1967) in second discovered similar FAP patients in Arao, Kumamoto, Japan. Owing to progress in biochemical and molecular genetic analyses, FAP is now believed to occur worldwide. As of today, reports of about 100 different points of single or two mutations, or a deletion in the transthyretin (TTR) gene, have been published. The authors' group has made pioneer works for study of FAP in the world. The focus on therapy in amylodosis will increase sharply as an impetus in near future, and successful treatments are expected.

Apolipoprotein E and amyloidogenesis

Alzheimer's amyloid beta-protein (A beta) is a modified, pathogenic form of a constitutive host protein, soluble amyloid beta-protein (sA beta). Both are conformational isomers encoded by the gene for the beta-amyloid precursor protein (APP), located on chromosome 21. sA beta and A beta have identical sequence but are thought to differ in their secondary structure and physicochemical properties, hence they are conformational isomers. sA beta is easily degraded, while A beta is particularly resistant. A beta has a high beta-pleated sheet content, while sA beta is thought to be more random-coil and/or alpha-helical. A beta, unlike sA beta, adopts an amyloidogenic conformation, forms aggregates and gives rise to fibrils. Most early-onset forms of Alzheimer's disease (AD) have been linked to mutations of the presenilin 1, presenilin 2 or APP genes, located on chromosomes 14, 1 and 21, respectively. Their relationship to amyloidogenesis is being investigated. On the other hand, the major risk factor for the most common form, sporadic and familial late-onset AD, is the presence of the apoE epsilon 4 allele. Recent studies have shown that a 10 kDa C-terminal fragment of apoE is complexed to A beta in neuritic plaques and that apoE isoforms can modulate amyloid formation in vitro. Moreover, thrombin cleavage of apoE generates a similar C-terminal fragment that can form amyloid-like fibrils. Thus neuritic plaques may contain both A beta and apoE amyloid fibrils. AD can be neuropathologically defined by the presence of several interacting proteins that can adopt an amyloidogenic conformation. This has led us to hypothesize that in AD, amyloidosis may be reactive rather than causative.

Interaction of transthyretin with amyloid beta-protein: binding and inhibition of amyloid formation

Aggregated amyloid beta-protein (A beta) is a key component of the amyloid depositions found in the brains of patients with Alzheimer's disease. In contrast, in cerebrospinal fluid (CSF), A beta is found in a soluble form. The analysis of complexes of A beta with CSF proteins in a KBr gradient revealed an association of A beta only with free proteins and not with lipoprotein particles. Transthyretin (TTR), a second major CSF protein, formed SDS-stable complexes with A beta and significantly decreased the rate of A beta fibril formation. In physiological buffers and CSF, TTR exclusively decreased the level of A beta pentamers. Endogenous TTR-A beta complexes were detected in human CSF by immunoprecipitation. Using site-directed mutagenesis and computer-assisted modelling, we identified amino acid residues on the surface of the TTR monomer that interact with A beta. Specific TTR immunoreactivity was detected in multiple cortical neurons and astrocytes in the human brain. We propose that A beta binding proteins play a key role in the modulation of A beta aggregation and normally prevent amyloid formation in biological fluids and in the brain.

Transthyretin and familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is an inherited autosomal dominant disease that is commonly caused by accumulation of deposits of transthyretin (TTR) amyloid around peripheral nerves. The only effective treatment for FAP is liver transplantation. However, recent studies on TTR aggregation provide clues to the mechanism of the molecular pathogenesis of FAP and suggest new avenues for therapeutic intervention. It is increasingly recognized that there are common features of a number of protein-misfolding diseases that can lead to neurodegeneration. As for other amyloidogenic proteins, the most toxic forms of aggregated TTR are likely to be the low-molecular-mass diffusible species, and there is increasing evidence that this toxicity is mediated by disturbances in calcium homeostasis. This article reviews what is already known about the mechanism of TTR aggregation in FAP and describes how recent discoveries in other areas of amyloid research, particularly Alzheimer's disease, provide clues to the molecular pathogenesis of FAP.

Diffuse metabolic changes in the brain of patients with familial amyloid polyneuropathy. A proton MRSI study

OBJECTIVES

To assess brain metabolic abnormalities in patients with familial amyloid polyneuropathy (FAP) due to the transthyretin (TTR) gene mutations.

BACKGROUND

The TTR-FAP has variable phenotypic expression, which includes abnormalities of the central nervous system (CNS). Several conventional MRI studies have shown brain abnormalities, probably secondary to amyloid accumulation in leptomeningeal and subarachnoid vessels. However, TTR-related amyloid deposits do not seem to significantly affect the brain parenchyma and a prominent CNS impairment is considered to be rare in TTR amyloidosis.

METHODS

We performed proton MR spectroscopic imaging (1H-MRSI) in the central brain of four unrelated TTR-FAP patients with either minimal or no signs of neurological involvement and eight age- and sex-matched normal controls (NC). Metabolic changes were assessed in the entire volume of interest (VOI) and in the frontal, periventricular and posterior white matter (WM).

RESULTS

Conventional MRI was normal in 2 patients and showed minimal WM lesions in the remaining 2 patients. 1H-MRSI showed N-acetylaspartate to creatine ratio (NAA/Cr) decreases in the central brain VOI in all TTR-FAP patients (p < 0.005). These NAA/Cr decreases were homogeneous in all WM regions (p < 0.05 for all).

CONCLUSIONS

1H-MRSI findings suggest that diffuse metabolic changes, probably related to axonal damage, are present in brains of TTR-FAP patients even when they have no or minimal clinical and MRI signs of CNS involvement. The mechanism leading to sub-clinical metabolic brain changes needs to be identified.

A different amyloid formation mechanism: de novo oculoleptomeningeal amyloid deposits after liver transplantation

BACKGROUND

Liver transplantation has served as a treatment for patients with familial amyloidotic polyneuropathy (FAP) because variant transthyretin (TTR), the pathogenic protein of FAP, is predominantly produced by the liver. However, the effect on amyloid formation of TTR that is synthesised by the retina and the choroid plexus remains to be elucidated in FAP patients with liver transplants.

OBJECTIVE

To investigate changes in ocular tissues and the central nervous system (CNS) of FAP patients after liver transplantation.

DESIGN

Clinical study.

SETTING

Graduate School of Medical Sciences, Kumamoto University, Japan.

INTERVENTION

Transplantation of livers from cadaveric or living donors.

MEASUREMENTS

Preoperative measures and postoperative (16-108 months) follow-up of clinical data, including routine ophthalmologic, neurologic, and laboratory evaluations.

RESULTS

In 22 patients with FAP related to the amyloidogenic TTR (ATTR) Val30Met and 3 patients with FAP ATTR Tyr114Cys, after liver transplantation, 3 patients began to show evidence of de novo glaucoma, and 1 had vitreous opacity that was caused by the variant TTR. Another three patients showed new amyloid deposits in the pupillary margin, which could lead to glaucoma and vitreous opacity. As for changes in the CNS and levels of total protein and TTR in cerebrospinal fluid (CSF), after liver transplantation, two FAP ATTR Tyr114Cys patients exhibited de novo amyloid deposition in the leptomeninges, and total protein and TTR levels in CSF were significantly increased.

CONCLUSIONS

Oculoleptomeningeal involvement in FAP was not prevented by liver transplantation because variant TTR produced by the retina and the choroid plexus forms amyloid fibrils in situ.

Postmortem findings in a familial amyloid polyneuropathy patient with homozygosity of the mutant Val30Met transthyretin gene

Autopsy findings in a 68-year-old FAP patient with a homozygous mutation of the Val30Met TTR gene were described. In addition to amyloid deposits on the visceral organs, peripheral nerves and the vitreous body, severe deposition of amyloid in the leptomeninges and subarachnoid vessels in the brain and spinal cord was present. A double dose of the mutant gene may accelerate amyloid deposition on the ocular and meningeal tissues.

Atypical familial motor neuropathy in patients with mutant TTR Ile68Leu

Two sisters from an Italian family shared progressive motor symptoms, preceding the onset of sensory and autonomic disturbances. The familial occurrence of axonal and slowly progressive polyneuropathy led us to consider these patients as candidates for TTR molecular analysis. We found a missense mutation causing Ile68Leu TTR substitution in both. The aims of this work are to report the possibility of a motor onset of amyloid polyneuropathy and to suggest the search for TTR mutations in familial cases of axonal polyneuropathy. Second, to stress the possible occurrence of amyloid within the spinal canal as the potential pathogenesis and responsible for motor presentation.

Energetic characteristics of the new transthyretin variant A25T may explain its atypical central nervous system pathology

Transthyretin (TTR) is a tetrameric protein that must misfold to form amyloid fibrils. Misfolding includes rate-limiting tetramer dissociation, followed by fast tertiary structural changes that enable aggregation. Amyloidogenesis of wild-type (WT) TTR causes a late-onset cardiac disease called senile systemic amyloidosis. The aggregation of one of > 80 TTR variants leads to familial amyloidosis encompassing a collection of disorders characterized by peripheral neuropathy and/or cardiomyopathy. Prominent central nervous system (CNS) impairment is rare in TTR amyloidosis. Herein, we identify a new A25T TTR variant in a Japanese patient who presented with CNS amyloidosis at age 42 and peripheral neuropathy at age 44. The A25T variant is the most destabilized and fastest dissociating TTR tetramer published to date, yet, surprising, disease onset is in the fifth decade. Quantification of A25T TTR in the serum of this heterozygote reveals low levels relative to WT, suggesting that protein concentration influences disease phenotype. Another recently characterized TTR CNS variant (D18G TTR) exhibits strictly analogous characteristics, suggesting that instability coupled with low serum concentrations is the signature of CNS pathology and protects against early-onset systemic amyloidosis. The low A25T serum concentration may be explained either by impaired secretion from the liver or by increased clearance, both scenarios consistent with A25T's low kinetic and thermodynamic stability. Liver transplantation is the only known treatment for familial amyloid polyneuropathy. This is a form of gene therapy that removes the variant protein from serum preventing systemic amyloidosis. Unfortunately, the choroid plexus would have to be resected to remove A25T from the CSF-the source of the CNS TTR amyloid. Herein we demonstrate that small-molecule tetramer stabilizers represent an attractive therapeutic strategy to inhibit A25T misfolding and CNS amyloidosis. Specifically, 2-[(3,5-dichlorophenyl)amino]benzoic acid is an excellent inhibitor of A25T TTR amyloidosis in vitro.

Clinical picture and outcome of transthyretin-related familial amyloid polyneuropathy (FAP) in Japanese patients

Familial amyloid polyneuropathy (FAP) was once considered to be a disease peculiar to endemic areas, but it is now recognized that FAP kindreds exist in worldwide places. The amyloid precursor of FAP is a variant form of transthyretin (TTR) with one amino acid substitution, which is ascribed to a mutation of TTR gene. Corresponding to the variety of the clinical phenotypes of FAP, more than 80 mutations have been identified as causative gene abnormality in this disease. Since the vast majority of TTR in serum is produced in the liver, liver transplantation has become widely accepted as a valuable treatment for FAP.

Dementia in hereditary cerebral hemorrhage with amyloidosis-Dutch type is associated with cerebral amyloid angiopathy but is independent of plaques and neurofibrillary tangles

Cerebral amyloid angiopathy is frequently found in demented and nondemented elderly persons, but its contribution to the causation of dementia is unknown. Therefore, we investigated the relation between the amount of cerebral amyloid angiopathy and the presence of dementia in 19 patients with hereditary cerebral hemorrhage with amyloidosis-Dutch type. The advantage of studying hereditary cerebral hemorrhage in amyloidosis-Dutch type is that patients with this disease consistently have severe cerebral amyloid angiopathy with minimal neurofibrillary pathology. The amount of cerebral amyloid angiopathy, as quantified by computerized morphometry, was strongly associated with the presence of dementia independent of neurofibrillary pathology, plaque density, or age. The number of cortical amyloid beta-laden severely stenotic vessels, vessel-within-vessel configurations, and cerebral amyloid angiopathy-associated microvasculopathies was associated with the amount of cerebral amyloid angiopathy and dementia. A semiquantitative score, based on the number of amyloid beta-laden severely stenotic vessels, completely separated demented from nondemented patients. These results suggest that extensive (more than 15 amyloid beta-laden severely stenotic vessels in five frontal cortical sections) cerebral amyloid angiopathy alone is sufficient to cause dementia in hereditary cerebral hemorrhage with amyloidosis-Dutch type. This may have implications for clinicopathological correlations in Alzheimer's disease and other dementias with cerebral amyloid angiopathy.

Cerebral amyloid angiopathy associated with hemorrhage: immunohistochemical study of 41 biopsy cases

The relationship between cerebral amyloid angiopathy and hemorrhage was investigated by an immunohistochemical study of biopsy cases to characterize the involvement of amyloid beta-protein, apolipoprotein E, and cystatin C in cerebral amyloid angiopathy associated with hemorrhage. The amyloid-laden vessels were examined in biopsy specimens from 41 surgical cases of sporadic cerebral amyloid angiopathy (36 cases with hemorrhage and 5 cases without hemorrhage), using immunohistochemical staining with antibodies against amyloid beta-protein, apolipoprotein E, cystatin C, and alpha-smooth muscle actin. The relationship between the occurrence, recurrence, and enlargement of the hemorrhage, and the semiquantitative estimation of the cerebrovascular amyloid-related protein deposition was analyzed using Fisher's exact test. Severe amyloid beta-protein (p < 0.013) and apolipoprotein E (p < 0.013) immunoreactivity were risk factors for the occurrence of the hemorrhage. Severe cystatin C immunoreactivity was a risk factor for the occurrence (p < 0.002) and enlargement (p < 0.014) of the hemorrhage, and tended to induce recurrent hemorrhage (p < 0.103). In addition, loss of the vascular smooth muscle was observed in the intensely amyloid-laden vascular walls that showed cystatin C-immunoreactivity. The present study indicates that intense amyloid beta-protein deposition with cystatin C deposition weakens the cerebrovascular walls, and that cystatin C deposition is a strong predictor of hemorrhage in cerebral amyloid angiopathy.

Variant transthyretin in blood circulation can transverse the blood-cerebrospinal barrier: qualitative analyses of transthyretin metabolism in sequential liver transplantation

BACKGROUND

Although the choroid6 plexus of the brain is one of the most important production sites of transthyretin (TTR), the metabolism of TTR secreted in cerebrospinal fluid (CSF) remains to be elucidated.

METHODS

To perform qualitative analysis of variant TTR in CSF of patients who underwent a sequential liver transplantation using an explanted familial amyloidotic polyneuropathy (FAP) ATTR Val30 Met patient's liver, levels and forms of TTR of the two patients were analyzed by means of enzyme linked immunosorbent assay (ELISA) and matrix-assisted laser desorption/time-of-flight mass spectrometer (MALDI/TOF-MS), respectively.

RESULTS

After the operation, variant TTR levels in serum increased, and in CSF, a significant peak of free form of ATTR Val30 Met was detected in the transplanted patients whose CSF had shown no variant TTR before the operation.

CONCLUSIONS

These findings suggest that the variant TTR can cross-the blood-CSF barrier and migrate into CSF from blood circulation. Because leptomeningeal amyloidosis occurs in FAP ATTR Val30 Met as the progression of the disease, this information suggests that in addition to peripheral neuropathy, disorders of the central nervous system (CNS) should be given an attention in patients who underwent sequential liver transplantation using an explanted FAP ATTR Val30 Met patient's liver.

Familial amyloidotic polyneuropathy (ATTR Val30Met) with widespread cerebral amyloid angiopathy and lethal cerebral hemorrhage

We report an autopsy case of familial amyloidotic polyneuropathy (FAP) with cerebral hemorrhage. A 38-year-old woman with a typical FAP pedigree started developing severe diarrhea and sensori-motor polyneuropathy at the age of 28 years; autonomic nervous system, heart and renal dysfunction manifested themselves in the following years. Genetic analysis revealed a single amino acid substitution at codon 30 of transthyretin (ATTR Val30Met). Ten years after her initial symptoms, the patient died of a sudden convulsive attack and respiratory failure. Autopsy revealed lethal cerebral hemorrhages and uremic lungs. Histochemical and immunohistochemical analyses revealed TTR-derived amyloid protein in every tissue examined, particularly in glomeruli and peripheral vessels. Severe meningo-cerebrovascular amyloidosis was also detected. Because uremia causes oxidative damage to the vascular system and amyloid formation is closely associated with oxidative stress, it is possible that uremic endothelial damage facilitated an unusual cerebral amyloid deposition. In typical FAP (ATTR Val30Met), cerebral amyloid angiopathy does not usually have clinical manifestations. However, cerebral amyloid angiopathy should be considered to explain FAP symptoms when some risk factors such as uremic vascular damage are accompanying features.

Postmortem findings in two familial amyloidosis patients with transthyretin variant Asp38Ala

Postmortem findings in 2 familial amyloidosis patients with the transthyretin variant (ATTR), Asp38Ala, are described Both showed cardiac failure, and progressive peripheral and autonomic neuropathy and died at the ages 82 and 57, respectively. TTR immunoreactive amyloid deposition was observed to be extensive in the myocardium, peripheral nerves, sympathetic ganglia and gastrointestinal tract. The pulmonary parenchyma was also diffusely involved, but renal glomeruli, follicular tissues of the thyroid, and the leptomeninges and subarachnoidal vessels of the central nervous system showed little deposition. The latter findings are not usually seen in the patients with ATTR Val30Met, the most common form of familial amyloidosis. Additionally, the clinicopathological findings of familial amyloidosis with ATTR Asp38Ala seem to vary in the different individuals.

Cerebral amyloid angiopathy: an overview

Cerebral amyloid angiopathy (CAA) is characterized by amyloid deposition in cortical and leptomeningeal vessels. Several cerebrovascular amyloid proteins (amyloid beta-protein (Abeta), cystatin C (ACys), prion protein (AScr), transthyretin (ATTR), gelsolin (AGel), and ABri (or A-WD)) have been identified, leading to the classification of several types of CAA. Sporadic CAA of Abeta type is commonly found in elderly individuals and patients with Alzheimer's disease. Cerebral amyloid angiopathy is an important cause of cerebrovascular disorders including lobar cerebral hemorrhage, leukoencephalopathy, and small cortical hemorrhage and infarction. We review the clinicopathological and molecular aspects of CAA and discuss the pathogenesis of CAA with future perspectives.

Transthyretin Leu12Pro is associated with systemic, neuropathic and leptomeningeal amyloidosis

We report a middle-aged woman with a novel transthyretin (TTR) variant, Leu12Pro. She had extensive amyloid deposition in the leptomeninges and liver as well as the involvement of the heart and peripheral nervous system which characterizes familial amyloid polyneuropathy caused by variant TTR. Clinical features attributed to her leptomeningeal amyloid included radiculopathy, central hypoventilation, recurrent subarachnoid haemorrhage, depression, seizures and periods of decreased consciousness. MRI showed a marked enhancement throughout her meninges and ependyma, and TTR amyloid deposition was confirmed by meningeal biopsy. The simultaneous presence of extensive visceral amyloid and clinically significant deposits affecting both the peripheral and central nervous system extends the spectrum of amyloid-related disease associated with TTR mutations. The unusual association of severe peripheral neuropathy with symptoms of leptomeningeal amyloid indicates that leptomeningeal amyloidosis should be considered part of the syndrome of TTR-related familial amyloid polyneuropathy.

No mutations in cystatin C gene in cerebral amyloid angiopathy with cystatin C deposition

To investigate the relationship between cerebral amyloid angiopathy (CAA) and cystatin C, we studied five CAA patients on whose cerebral blood vessels colocalization of cystatin C and beta-protein was recognized immunohistochemically. One patient was suspected as familial CAA and the other patients were sporadic cases. Two patients had low concentration of cystatin C in their cerebrospinal fluid (CSF) as we have previously reported in CAA patients. Enzyme-linked immunosorbent assay (ELISA) revealed that cystatin C and beta-protein have been included at the ratio of about 1:100 in the crude amyloid fibrils of one patient. Using a monoclonal antibody (MAb) against cystatin C, we performed affinity chromatography and immunoblotting on her amyloid fibril fraction. Eluate showed a band with a mol wt of 14,000 and the N-terminal 14 amino acid residues of 14-kDa protein were identical with that of cystatin C. This molecular weight is not identical to that of the truncated form of cystatin C deposited in hereditary cerebral hemorrhage with amyloidosis in Iceland (HCHWA-I), but that of normal cystatin C. DNA sequence analysis of five patients showed no point mutations in the cystatin C gene. Cystatin C and beta-protein colocalization, which was recognized in amyloid lesions of CAA, suggests that cystatin C deposition may be related to beta-protein deposition. We hypothesize that cystatin C deposition in sporadic cerebral amyloid angiopathy with cystatin C deposition (SCCAA) involves a different mechanism from that in HCHWA-I, which may be related to low CSF concentration of cystatin C without amino acid substitutions.

Hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D): II--A review of histopathological aspects

Cerebral amyloid-beta (A beta) angiopathy is the histopathological hallmark of hereditary cerebral hemorrhage with amyloidosis (Dutch) (HCHWA-D). A beta deposits are found mainly in the cerebral and cerebellar meningocortical blood vessels and as plaques throughout the cerebrocortical gray matter. A beta deposition in arteries and arterioles starts at the junction of media and adventitia and proceeds to involve the media causing degeneration of the vascular smooth muscle cells. Cerebrocortical arterioles often show one or two layers of radial A beta around a layer of homogenous A beta that replaces the media. Degenerating neurites, reactive astrocytes and microglial cells may surround cerebrocortical angiopathic arterioles and capillaries, probably in reaction to invasion of the perivascular neuropil by A beta fibrils. Furthermore, clusters of coarse extracellular matrix deposits may be found near A beta-laden cerebrocortical arterioles. The amyloid-associated proteins, cystatin C, and beta PP colocalize diffusely with Dutch vascular A beta, whereas HLA-DR immunoreactivity is found only in the periphery of the diseased vessel wall. The latter phenomenon may be related to the presence of perivascular cells. Angiopathic blood vessels frequently show structural changes. The relation of the described pathology to the development of hemorrhage, infarction and leukoencephalopathy needs further elucidation.

Vascular variant of prion protein cerebral amyloidosis with tau-positive neurofibrillary tangles: the phenotype of the stop codon 145 mutation in PRNP

Deposition of PrP amyloid in cerebral vessels in conjunction with neurofibrillary lesions is the neuropathologic hallmark of the dementia associated with a stop mutation at codon 145 of PRNP, the gene encoding the prion protein (PrP). In this disorder, the vascular amyloid in tissue sections and the approximately 7.5-kDa fragment extracted from amyloid are labeled by antibodies to epitopes located in the PrP sequence including amino acids 90-147. Amyloid-laden vessels are also labeled by antibodies against the C terminus, suggesting that PrP from the normal allele is involved in the pathologic process. Abundant neurofibrillary lesions are present in the cerebral gray matter. They are composed of paired helical filaments, are labeled with antibodies that recognize multiple phosphorylation sites in tau protein, and are similar to those observed in Alzheimer disease. A PrP cerebral amyloid angiopathy has not been reported in diseases caused by PRNP mutations or in human transmissible spongiform encephalopathies; we propose to name this phenotype PrP cerebral amyloid angiopathy (PrP-CAA).

Characterization of a transthyretin-related amyloid fibril protein from cerebral amyloid angiopathy in type I familial amyloid polyneuropathy

Recently, it has been reported that transthyretin (TTR)-immunoreactive amyloid deposition with cerebral amyloid angiopathy in central nervous system is a common pathological finding in type I familial amyloid polyneuropathy (FAP). In the present study, we performed isolation and sequence analysis of TTR-related amyloid fibril protein from the meninges of a patient with type I FAP. Purified major amyloid fibril protein had a molecular weight of 15 kDa. Complete sequence analysis revealed that this amyloid fibril protein was a variant TTR with a single amino acid substitution of methionine for valine at position 30. This variant TTR is a previously unrecognized as cerebrovascular amyloid fibril protein. Furthermore, the patients with type I FAP are well known to have the variant TTR in the serum. These suggest that cerebrovascular amyloid fibril protein in type I FAP may derive from a serum precursor.