Neuropathology of central nervous system involvement in TTR amyloidosis

Is CAA a perivascular brain clearance disease? A discussion of the evidence to date and outlook for future studies

The brain's network of perivascular channels for clearance of excess fluids and waste plays a critical role in the pathogenesis of several neurodegenerative diseases including cerebral amyloid angiopathy (CAA). CAA is the main cause of hemorrhagic stroke in the elderly, the most common vascular comorbidity in Alzheimer's disease and also implicated in adverse events related to anti-amyloid immunotherapy. Remarkably, the mechanisms governing perivascular clearance of soluble amyloid β-a key culprit in CAA-from the brain to draining lymphatics and systemic circulation remains poorly understood. This knowledge gap is critically important to bridge for understanding the pathophysiology of CAA and accelerate development of targeted therapeutics. The authors of this review recently converged their diverse expertise in the field of perivascular physiology to specifically address this problem within the framework of a Leducq Foundation Transatlantic Network of Excellence on Brain Clearance. This review discusses the overarching goal of the consortium and explores the evidence supporting or refuting the role of impaired perivascular clearance in the pathophysiology of CAA with a focus on translating observations from rodents to humans. We also discuss the anatomical features of perivascular channels as well as the biophysical characteristics of fluid and solute transport.

Neurofilament Light Chains in Systemic Amyloidosis: A Systematic Review

Peripheral and autonomic neuropathy are common disease manifestations in systemic amyloidosis. The neurofilament light chain (NfL), a neuron-specific biomarker, is released into the blood and cerebrospinal fluid after neuronal damage. There is a need for an early and sensitive blood biomarker for polyneuropathy, and this systematic review provides an overview on the value of NfL in the early detection of neuropathy, central nervous system involvement, the monitoring of neuropathy progression, and treatment effects in systemic amyloidosis. A literature search in PubMed, Embase, and Web of Science was performed on 14 February 2024 for studies investigating NfL levels in patients with systemic amyloidosis and transthyretin gene-variant (TTRv) carriers. Only studies containing original data were included. Included were thirteen full-text articles and five abstracts describing 1604 participants: 298 controls and 1306 TTRv carriers or patients with or without polyneuropathy. Patients with polyneuropathy demonstrated higher NfL levels compared to healthy controls and asymptomatic carriers. Disease onset was marked by rising NfL levels. Following the initiation of transthyretin gene-silencer treatment, NfL levels decreased and remained stable over an extended period. NfL is not an outcome biomarker, but an early and sensitive disease-process biomarker for neuropathy in systemic amyloidosis. Therefore, NfL has the potential to be used for the early detection of neuropathy, monitoring treatment effects, and monitoring disease progression in patients with systemic amyloidosis.

Origin of Transthyretin in Cerebral Amyloid Angiopathy

This case series evaluates the correlation between transthyretin and cerebral amyloid angiopathy progression in individuals with hereditary transthyretin amyloidosis.

Nerve pathology of microangiopathy and thromboinflammation in hereditary transthyretin amyloidosis

OBJECTIVE

Despite amyloid deposition as a hallmark of hereditary transthyretin amyloidosis (ATTRv) with polyneuropathy, this pathology could not completely account for nerve degeneration. ATTRv patients frequently have vasomotor symptoms, but microangiopathy hypothesis in ATTRv was not systemically clarified.

METHODS

This study examined the vascular pathology of sural nerves in ATTRv patients with transthyretin (TTR) mutation of p.Ala117Ser (TTR-A97S), focusing on morphometry and patterns of molecular expression in relation to nerve degeneration. We further applied human microvascular endothelial cell (HMEC-1) culture to examine the direct effect of TTR-A97S protein on endothelial cells.

RESULTS

In ATTRv nerves, there was characteristic microangiopathy compared to controls: increased vessel wall thickness and decreased luminal area; both were correlated with the reduction of myelinated fiber density. Among the components of vascular wall, the area of collagen IV in ATTRv nerves was larger than that of controls. This finding was validated in a cell model of HMEC-1 culture in which the expression of collagen IV was upregulated after exposure to TTR-A97S. Apoptosis contributed to the endothelial cell degeneration of microvasculatures in ATTRv endoneurium. ATTRv showed prothrombotic status with intravascular fibrin deposition, which was correlated with (1) increased tissue factor and coagulation factor XIIIA and (2) reduced tissue plasminogen activator. This cascade led to intravascular thrombin deposition, which was colocalized with upregulated p-selectin and thrombomodulin, accompanied by complement deposition and macrophages infiltration, indicating thromboinflammation in ATTRv.

INTERPRETATION

Microangiopathy with thromboinflammation is characteristic of advanced-stage ATTRv nerves, which provides an add-on mechanism and therapeutic target for nerve degeneration.

Hereditary transthyretin amyloid neuropathies: advances in pathophysiology, biomarkers, and treatment

Hereditary transthyretin (TTR) amyloid polyneuropathy is an autosomal dominant life-threatening disorder. TTR is produced mainly by the liver but also by the choroid plexus and retinal pigment epithelium. Detailed clinical characterisation, identification of clinical red flags for misdiagnosis, and use of biomarkers enable early diagnosis and treatment. In addition to liver transplantation and TTR stabilisers, three other disease-modifying therapies have regulatory approval: one antisense oligonucleotide (inotersen) and two small interfering RNAs (siRNAs; patisiran and vutrisiran). The siRNAs have been shown to stop progression of neuropathy and improve patients' quality of life. As none of the disease-modifying therapies can cross the blood-brain barrier, TTR deposition in the CNS, which can cause stroke and cognitive impairment, remains an important unaddressed issue. CRISPR-Cas9-based one-time TTR editing therapy is being investigated in a phase 1 clinical study. Identification of the earliest stages of pathogenesis in TTR variant carriers is a major challenge that needs addressing for optimal management.

[Case of hereditary Y69H (p.Y89H) transthyretin variant leptomeningeal amyloidosis presenting with drop attacks and recurrent transient language disorder]

We report a 73-year-old woman who started developing recurrent transient aphasia at the age of 66 years. During the attacks, she was aware she could not understand what was being said and both her spoken and written speech were meaningless. The attacks usually lasted for a few days, following which she could explain what had happened. Anti-epileptics did not improve her symptoms. She also noticed tremor of her right hand and gait disturbance at the age of 71 years. The recurrent transient aphasia was followed by drop attacks. At the time of her admission to our hospital, she showed paraplegia, phonological paraphasia, and difficulty in understanding complex sentences. Her language disturbance resembled a logopenic variant of primary progressive aphasia. However, the symptoms fluctuated for a few days and subsequently improved. Electroencephalography showed no abnormalities. Gadolinium-enhanced brain and spinal MRI showed diffuse leptomeningeal enhancement over the surface of the spinal cord, brain stem, and cerebrum on T1-weighed imaging. Surgical biopsy of a varicose vein in the subarachnoid space at the level of the Th11 spinal cord was performed. Pathological evaluation of the biopsied specimens revealed TTR-immunolabeled amyloid deposits in the subarachnoid vessel walls and on the arachnoid membrane. Gene analysis revealed c.265T>C, p.Y89H (Y69H) TTR mutation, which is known as one of the causative mutations of familial leptomeningeal amyloidosis. Leptomeningeal forms of transthyretin amyloidosis might present transient focal neurological episodes.

Unusual localization and clinical presentation of primary central nervous system extranodal marginal zone B‑cell lymphoma: A case report

Primary central nervous system (CNS) extranodal marginal zone B-cell lymphoma (MZBL) is a rare low-grade non-Hodgkin lymphoma, characterised predominantly by small B cells, plasma cells, monocytoid cells and scattered large immunoblasts. Primary CNS MZBL is a slow-growing tumour that remains localised and is characterised by an excellent clinical prognosis. The present study describes the case of a 48-year-old HIV-negative female patient with a history of head trauma 1 year prior, who presented with worsening neurological symptoms and a magnetic resonance imaging finding of a ~3-cm extra-axial mass within the left lateral ventricle. From histopathology and immunohistochemistry, the lesion was diagnosed as a CNS MZBL; as no other primary lesions were found, the base of the choroid plexuses of the left lateral ventricle was considered the primary site. To the best of our knowledge, the current case is the first study to report on primary CNS MZBL arising in this anatomical site and paves the way for further studies on the role of chronic inflammation (in the present case resulting from trauma) in the pathogenesis not only of primary CNS MZBL but also of lymphoma in general. Additionally, this report could serve as a starting point for studies analysing the role of meningothelial cells in the pathogenesis of primary CNS MZBL.

The Transthyretin Amyloidosis - Quality of Life (ATTR-QOL) Questionnaire: Development of a Conceptual Model and Disease-Specific Patient-Reported Outcome Measure

Purpose

Patients with transthyretin amyloidosis (ATTR) experience a wide variety of symptoms and impacts on health-related quality of life (HRQoL). However, the lack of an ATTR-specific patient-reported outcome (PRO) measure has made consistent measurement of HRQoL in ATTR challenging. This paper describes the development of a conceptual model and subsequent content for the Transthyretin Amyloidosis - Quality of Life Questionnaire (ATTR-QOL), an ATTR-specific PRO measure.

Methods

This was a cross-sectional, non-interventional, US-based study. The study design included three stages: 1) a targeted literature review followed by qualitative data collection with patients and experts; 2) development of a conceptual model and PRO measure; and 3) review of the PRO measure using a modified Delphi method, translatability assessment, and interviews with patients and experts. Revisions were made to the measure after each round of review.

Results

Forty-four patients and 29 experts participated in this study. The conceptual model included two primary concepts of interest: symptoms (cardiac, neuropathic-peripheral, neuropathic-autonomic, and other) and impacts (eg, physical, role, and mental/emotional functioning). Seventy-two items were created (32 symptoms; 40 impacts) to align with the model. A recall period of one month was selected based on participant input.

Conclusion

The ATTR-QOL was created with significant patient involvement and guidance from a multidisciplinary group of experts. The mix of patient and clinical perspectives helped to ensure a balanced representation of all relevant disease experiences and clinical specialties. With further refinement from psychometric testing, the ATTR-QOL will provide a standard, comprehensive measure for all ATTR-specific research including both clinical trials and clinical practice.