Neurophysiological markers in familial amyloid polyneuropathy patients: Early changes

Cardiovascular autonomic failure in hereditary transthyretin amyloidosis and TTR carriers is an early and progressive disease marker

BACKGROUND

The cardiomyopathic and neuropathic phenotype of hereditary transthyretin amyloidosis are well recognized. Cardiovascular autonomic dysfunction is less systematically and objectively assessed.

METHODS

Autonomic and clinical features, quantitative cardiovascular autonomic function, and potential autonomic prognostic markers of disease progression were recorded in a cohort of individuals with hereditary transthyretin amyloidosis and in asymptomatic carriers of TTR variants at disease onset (T0) and at the time of the first quantitative autonomic assessment (T1). The severity of peripheral neuropathy and its progression was stratified with the polyneuropathy disability score.

RESULTS

A total of 124 individuals were included (111 with a confirmed diagnosis of hereditary transthyretin amyloidosis, and 13 asymptomatic carriers of TTR variants). Symptoms of autonomic dysfunction were reported by 27% individuals at T0. Disease duration was 4.5 ± 4.0 years [mean ± standard deviation (SD)] at autonomic testing (T1). Symptoms of autonomic dysfunction were reported by 78% individuals at T1. Cardiovascular autonomic failure was detected by functional testing in 75% individuals and in 64% of TTR carriers. Progression rate from polyneuropathy disability stages I/II to III/IV seemed to be shorter for individuals with autonomic symptoms at onset [2.33 ± 0.56 versus 4.00 ± 0.69 years (mean ± SD)].

CONCLUSIONS

Cardiovascular autonomic dysfunction occurs early and frequently in individuals with hereditary transthyretin amyloidosis within 4.5 years from disease onset. Cardiovascular autonomic failure can be subclinical in individuals and asymptomatic carriers, and only detected with autonomic function testing, which should be considered a potential biomarker for early diagnosis and disease progression.

Canadian Guidelines for Hereditary Transthyretin Amyloidosis Polyneuropathy Management

Hereditary transthyretin-mediated (hATTR) amyloidosis is a progressive disease caused by mutations in the TTR gene leading to multisystem organ dysfunction. Pathogenic TTR aggregation, misfolding, and fibrillization lead to deposition of amyloid in multiple body organs and frequently involve the peripheral nerve system and the heart. Common neurologic manifestations include: sensorimotor polyneuropathy (PN), autonomic neuropathy, small-fiber PN, and carpal tunnel syndrome. Many patients have significant progression due to diagnostic delays as hATTR PN is not considered within the differential diagnosis. Recently, two effective novel disease-modifying therapies, inotersen and patisiran, were approved by Health Canada for the treatment of hATTR PN. Early diagnosis is crucial for the timely introduction of these disease-modifying treatments that reduce impairments, improve quality of life, and extend survival. In this guideline, we aim to improve awareness and outcomes of hATTR PN by making recommendations directed to the diagnosis, monitoring, and treatment in Canada.

Corneal sub-basal whorl-like nerve plexus: a landmark for early and follow-up evaluation in transthyretin familial amyloid polyneuropathy

BACKGROUND AND PURPOSE

Small-fiber nerves are the first to be involved in transthyretin familial amyloid polyneuropathy (TTR-FAP) patients. In vivo corneal confocal microscopy (CCM) is a noninvasive technique to detect small-fiber polyneuropathy (SFN) by quantifying corneal nerve morphology. The characteristic whorl-like pattern of the corneal nerve provides a static landmark for observation. We aimed to evaluate whether CCM images of the whorl-like plexus can sensitively evaluate and monitor disease progression in FAP patients.

METHODS

Fifteen FAP patients and 15 controls underwent neurological evaluation and CCM observation. Corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD) detected by conventional method and inferior whorl length (IWL), inferior whorl fiber density (IWFD), and inferior whorl branch density (IWBD) were compared in controls and patients. The Langerhans cell (LC) density in each image was calculated.

RESULTS

All CCM parameters were significantly reduced with disease progression. Preclinical patients had significantly lower IWL (P = 0.008) than age-matched controls. IWL (P = 0.006), CNFL (P = 0.005), CNBD (P = 0.008), and CNFD (P = 0.014) were significantly lower in early-phase patients. LC density was significantly increased around the central whorl in early-phase patients and was relatively lower in progressive patients. Both IWL and CNFL correlated with the severity of neuropathy, and IWL was more significantly reduced. The area under the receiver operating characteristic (ROC) curve for FAP with CNFL and IWL was 88.0% (95% CI, 70.9%-96.9%) and 89.3% (95% CI, 72.6%-97.6%), respectively, exceeding other parameters.

CONCLUSIONS

IWL is a more sensitive surrogate to detect preclinical SFN in FAP and can best discriminate patients from controls. The clustering of immature LCs at the inferior whorl area might reflect the inflammatory response of small-fiber nerves at the early stage.

Motor excitability measurements in early stage familial amyloid polyneuropathy: The influence of tafamidis treatment

OBJECTIVE

To test motor fiber excitability in early affected patients with transthyretin (TTR)-type familial amyloid polyneuropathy (TTR-FAP) before and during tafamidis treatment.

METHODS

We examined the left median nerve of 21 healthy-matched controls and 10 early affected TTR-FAP patients using the automated threshold-tracking program, QTRAC. TTR-FAP patients were tested one day before the initiation of tafamidis treatment, 3 and 6 months later.

RESULTS

The drug was well-tolerated in all patients; there was no drop-out. No statistical difference was found between healthy controls and TTR-FAP patients at study entry. On treatment, both stimulus intensity for 50% of the maximal motor response and rheobase increased significantly from entry to the last evaluation at 6 months (P<0.05). Strength duration time constant decreased significantly from the 3rd to the 6th month of evaluation (P<0.05). There was also a "fanning-out" effect on the late depolarization phase (TEd 90-100ms) as well as a shortened relative refractory period from study entry to the 6th month of evaluation.

CONCLUSIONS

Threshold-tracking of median nerve motor fibers is not a helpful technique for the early diagnosis of TTR-FAP patients. Tafamidis was well-tolerated. We observed possible membrane hyperpolarization during treatment. Threshold tracking can contribute to documenting the action of new drugs to treat neuropathies. Tafamidis may change nerve electrical properties by reducing the burden of amyloid fibrils.

Skin nerve pathology: Biomarkers of premanifest and manifest amyloid neuropathy

OBJECTIVE

Small-fiber sensory and autonomic symptoms are early presentations of familial amyloid polyneuropathy (FAP) with transthyretin (TTR) mutations. This study aimed to explore the potential of skin nerve pathologies as early and disease-progression biomarkers and their relationship with skin amyloid deposits.

METHODS

Skin biopsies were performed in patients and carriers to measure intraepidermal nerve fiber (IENF) density, sweat gland innervation index of structural protein gene product 9.5 (SGII[PGP9.5]) and peptidergic vasoactive intestinal peptide (SGII[VIP]), and cutaneous amyloid index. These skin pathologies were analyzed with clinical disability assessed by FAP stage score (stage 0-4) and compared to neurophysiological and psychophysical tests.

RESULTS

There were 70 TTR-mutant subjects (22 carriers and 48 patients), and 66 cases were TTR-A97S. Skin nerve pathologies were distinct according to stage. In carriers, both skin denervation and peptidergic sudomotor denervation were evident: (1) IENF density was gradually reduced from stage 0 through 4, and (2) SGII(VIP) was markedly reduced from stage 1 to 2. In contrast, SGII(PGP9.5) was similar between carriers and controls, but it declined in patients from stage 2. Skin amyloids were absent in carriers and became detectable from stage 1. Cutaneous amyloid index was correlated with SGII(PGP9.5) and stage in a multivariate mixed-effect model. When all tests were compared, only IENF density, SGII(PGP9.5), and cutaneous amyloid index were correlated with stage, and IENF density had the highest abnormal rate in carriers.

INTERPRETATION

Biomarkers of sensory and sudomotor innervation exhibited a stage-dependent progression pattern, with sensory nerve degeneration as the early skin nerve pathology. Ann Neurol 2019;85:560-573.

The value of electrochemical skin conductance measurement using Sudoscan® in the assessment of patients with familial amyloid polyneuropathy

OBJECTIVE

To reappraise the value of electrochemical skin conductance (ESC) measurement by Sudoscan® to assess the distal involvement of small autonomic fibers in familial amyloid polyneuropathy (FAP) due to various transthyretin (TTR) mutations.

METHODS

ESC was measured at both hands and feet in 126 patients with either Val30Met (n = 65) or non-Val30Met (n = 61) TTR mutation. This series included clinically asymptomatic (n = 21) and paucisymptomatic (n = 30) patients, as well as patients with moderate (n = 37) or advanced (n = 38) TTR-FAP.

RESULTS

ESC measures did not differ between patients according to the type of TTR variant and were reduced in 24% of clinically asymptomatic patients, 40% of paucisymptomatic patients, 65% of patients with moderate TTR-FAP, and 92% of patients with advanced TTR-FAP. ESC measures were found to correlate with patients' clinical status, especially assessed by the Neuropathy Impairment Score and Karnofsky Performance Status.

CONCLUSION

ESC measures well correlate with the severity of TTR-FAP and could provide early marker of the disease.

SIGNIFICANCE

ESC measures appear to be relevant to evaluate distal autonomic involvement in the context of amyloidosis.

Evidence of neurophysiological improvement of early manifestations of small-fiber dysfunction after liver transplantation in a patient with familial amyloid neuropathy

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Detecting signs of neuropathy helps therapeutic decisions in familial amyloidosis.

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Psychophysical thermal testing may be the only test showing damage in small fibers.

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Quantitative signs of improvement may remain a few years after liver transplantation.

Introduction

Small fiber polyneuropathy (SFP) is a common heralding clinical manifestation of damage to the nervous system in patients with familial amyloidosis. The diagnosis of SFP is a significant factor in the decision to treat a previously asymptomatic gene carrier, as treatment would prevent irreversible nerve damage. This requires detection of the earliest but unequivocal signs of peripheral nerve involvement.

Case report

We present the case of a young female who was diagnosed of SFP, supported by data from quantitative sensory testing. She had preserved sensory nerve action potentials in the distalmost nerves of her feet and recordable nociceptive evoked potentials. She was successfully transplanted the liver from a previously healthy donor, and recovered fully of her symptoms and signs. Improvement was documented with repeated psychophysical and electrodiagnostic testing in the course of 4 years after transplantation.

Significance

This case illustrates the utility of psychophysical testing to support the diagnosis of SFP.

Current and Future Treatment Approaches in Transthyretin Familial Amyloid Polyneuropathy

OPINION STATEMENT

Treatment of transthyretin familial amyloid polyneuropathy (TTR FAP) must be tailored to disease stage. Patients with early stage disease (i.e., without major impairment in walking ability), especially younger patients, should be referred as soon as possible for liver transplantation (LT) in the absence of major comorbid conditions. LT remains the most effective treatment option to date and should be offered to these patients as early as possible. Bridging therapy with an oral TTR stabilizer (tafamidis or diflunisal, according to local access to these treatments) should be started as soon as the diagnosis of TTR FAP is established. Early stage patients who do not wish to or have contraindications to LT should be treated with an oral TTR stabilizer or get access to the newly developed therapeutic options (IONIS TTR-Rx, patisiran, doxycycline/TUDCA). Late stage patients (presenting with significant walking impairment) are usually older and notoriously difficult to treat. They should be offered an oral TTR stabilizer but are not candidates for LT due to a significant rate of perioperative complications and increased risk of progressive neurological and especially cardiac disease despite LT. Access to the different therapies in development should also be considered depending on respective inclusion and exclusion criteria. The abovementioned treatment options were mostly validated in Val30Met mutation patients, but should also be offered to non-Val30Met patients, although mortality rates after LT are higher in these patients. Treatment decisions should be made on an individual basis. Screening for heart, eye, and renal involvement is mandatory for every patient at disease diagnosis and regularly thereafter, even in transplanted patients. Symptomatic treatment should be offered as needed, as well as genetic counseling to at-risk family members. Asymptomatic mutation carriers should benefit from regular screening for early symptoms of disease. Current therapeutic management of TTR FAP will hopefully be changed in the near future with data from the ongoing phase 2/3 studies testing the TTR gene silencing agents. In the longer term, it is likely that combined therapeutic approaches will be necessary to reverse the disease process.

The Temporal Profiles of Changes in Nerve Excitability Indices in Familial Amyloid Polyneuropathy

Familial amyloid polyneuropathy (FAP) caused by a mutation in transthyretin (TTR) gene is an autosomal dominant inherited disorder. The aim of this study is to explore the pathophysiological mechanism of FAP. We prospectively recruited 12 pauci-symptomatic carriers, 18 patients who harbor a TTR mutation, p.A97S, and two-age matched control groups. Data of nerve excitability test (NET) from ulnar motor and sensory axons were collected.NET study of ulnar motor axons of patients shows increased threshold and rheobase, reduced threshold elevation during hyperpolarizing threshold electrotonus (TE), and increased refractoriness. In sensory nerve studies, there are increased threshold reduction in depolarizing TE, lower slope of recovery and delayed time to overshoot after hyperpolarizing TE, increased refractoriness and superexcitability in recovery cycle. NET profiles obtained from the ulnar nerve of carriers show the increase of threshold and rheobase, whereas no significant threshold changes in hyperpolarizing TE and superexcitability. The regression models demonstrate that the increase of refractoriness and prolonged relative refractory period are correlated to the disease progression from carriers to patients. The marked increase of refractoriness at short-width stimulus suggests a defect in sodium current which may represent an early, pre-symptomatic pathophysiological change in TTR-FAP. Focal disruption of basal lamina and myelin may further increase the internodal capacity, manifested by the lower slope of recovery and delayed time to overshoot after hyperpolarization TE as well as the increase of superexcitability. NET could therefore make a pragmatic tool for monitoring disease progress from the very early stage of TTR-FAP.

Genotype-phenotype correlation and course of transthyretin familial amyloid polyneuropathies in France

OBJECTIVE

To compare the natural history of familial transthyretin amyloid polyneuropathies (FAP) due to the Val30Met, Ser77Tyr, and Ile107Val mutations in France with the classical Portuguese Val30Met FAP.

METHODS

We compared 84 French patients with a control group of 110 Portuguese patients carrying the Val30Met mutation also living in France, all referred to and followed at the French National FAP Reference Center from 1988 to 2010. Clinical examination, functional and walking disability scores, nerve conduction studies, and muscle biopsies are reported. We also conducted a comprehensive literature review to further determine the range of phenotypic expression.

RESULTS

By comparison with Portuguese Val30Met FAP, French Ile107Val, Ser77Tyr, and LateVal30Met FAP showed more rapid and severe disease progression; onset of gait disorders was 3 times more rapid (p < 0.0001) and the rate of modified Norris test decline was up to 40 times faster in Ile107Val patients (p < 0.0001). Median survival was much shorter in Ile107Val and in Val30Met mutation with late onset (>50 years; LateMet30) FAP (p = 0.0005). Other distinctive features relative to the Portuguese patients included atypical clinical presentations, demyelination on nerve conduction studies (p = 0.0005), and difficult identification of amyloid deposits in nerve and muscle biopsies.

INTERPRETATION

Ile107Val and LateMet30 mutations are associated with the most debilitating and severe FAP ever described, with rapid onset of tetraparesis and shorter median survival. It could be explained by frequent large-fiber involvement and associated demyelination and more severe axonal loss. These findings have major implications for genetic counseling and patient management as new therapeutic options are being assessed in clinical trials (TTR gene silencing).

Neurophysiological techniques to detect early small-fiber dysfunction in transthyretin amyloid polyneuropathy

INTRODUCTION

Transthyretin familial amyloid polyneuropathy (TTR-FAP) is characterized by early selective involvement of small nerve fibers. Initial clinical diagnosis is complicated by psychosocial factors. We evaluated diagnostic accuracy of sural sensory nerve action potentials, plantar sympathetic skin response (SSR), and cortical laser-evoked potentials (LEP) to dorsal foot stimulation in the early diagnosis of TTR-FAP.

METHODS

Sixty-three subjects with TTR-FAP (Val30Met) mutation were split into 2 groups (asymptomatic carriers and early-symptomatic patients) and compared with 33 healthy controls.

RESULTS

The diagnostic accuracy of plantar SSR amplitude and LEP N2 latency was similar; all had very high specificity (94 to 97%) but low sensitivity (22 to 32%) in distinguishing controls from carriers and early-symptomatic patients. No control had abnormal results on both tests.

CONCLUSIONS

Plantar SSR and LEPs have similar diagnostic performance in detecting small-fiber dysfunction in early TTR-FAP; we propose that both tests should be used to investigate this population. Muscle Nerve 49: 181-186, 2014.

Transthyretin familial amyloid polyneuropathy

TTR FAP is characterized by phenotypic and genotypic heterogeneity. The severity of polyneuropathy along with autonomic dysfunction and heart involvement makes it a life-threatening disease. This protein is mainly produced by the liver. Molecular genetic testing is essential in the diagnostic strategy. TTR-Val30Met is the most frequent substitution, resulting in a guanine to cytosine mutation in exon 2 of the gene. It is virtually the only variant detected in Portugal, Brazil, and Sweden. By contrast, as many as 30 different TTR variants are reported in Japan and in other European countries. A less severe phenotype with late onset has been reported. Diagnosis should be performed as early as possible since upcoming pharmacological therapeutic approaches are now available, in addition to liver transplantation.

α-Synuclein aggregation in the saliva of familial transthyretin amyloidosis: a potential biomarker

Familial transthyretin amyloidosis (ATTR) is an autosomal dominant disease characterized by the formation of transthyretin (TTR) amyloid deposits. This crippling and fatal disease is associated with point mutations in TTR, a protein mainly produced in the liver. Hence, liver transplantation is the only treatment capable of halting disease progression. Ideally, liver transplantation should be performed as early as possible in the disease course before significant neurologic disability has been incurred. Early detection of disease before serious pathological lesions occur is crucial for the clinical management of patients and for morbidity delay. Unfortunately, the presence of TTR mutations by itself is not a predictor of disease onset or progression. In the present work, we observed an increased oligomerization of α-synuclein in the saliva of ATTR symptomatic individuals comparatively to asymptomatic carriers of the same TTR mutation and healthy control subjects. Based on this observation, we propose monitoring α-synuclein oligomers in saliva as a biomarker of ATTR progression. Since α-synuclein plays a major role in several neurodegenerative disorders, assessing its oligomerization state in this fluid provides a non-invasive approach to survey these pathologies.

Familial amyloid polyneuropathy

Familial amyloid polyneuropathies (FAPs) are a group of life-threatening multisystem disorders transmitted as an autosomal dominant trait. Nerve lesions are induced by deposits of amyloid fibrils, most commonly due to mutated transthyretin (TTR). Less often the precursor of amyloidosis is mutant apolipoprotein A-1 or gelsolin. The first identified cause of FAP-the TTR Val30Met mutation-is still the most common of more than 100 amyloidogenic point mutations identified worldwide. The penetrance and age at onset of FAP among people carrying the same mutation vary between countries. The symptomatology and clinical course of FAP can be highly variable. TTR FAP typically causes a nerve length-dependent polyneuropathy that starts in the feet with loss of temperature and pain sensations, along with life-threatening autonomic dysfunction leading to cachexia and death within 10 years on average. TTR is synthesised mainly in the liver, and liver transplantation seems to have a favourable effect on the course of neuropathy, but not on cardiac or eye lesions. Oral administration of tafamidis meglumine, which prevents misfolding and deposition of mutated TTR, is under evaluation in patients with TTR FAP. In future, patients with FAP might benefit from gene therapy; however, genetic counselling is recommended for the prevention of all types of FAP.

Comparison of quantitative sensory testing and heart rate variability in Swedish Val30Met ATTR

Patients with transthyretin amyloidosis (ATTR) polyneuropathy, a hereditary fatal disease, often report defects in both thermal perception and autonomic nervous system function as their first clinical symptoms. While elevated thermal perception thresholds (TPT) for cold and warmth only recently have been shown as an early marker of small nerve fiber dysfunction in these patients, heart rate variability (HRV) has frequently been used to quantify autonomic neuropathy. The main purpose with this report was to elucidate a possible relationship between estimates of HRV and TPT in a selected group of early and late-onset Swedish Val30Met ATTR patients. The results show significantly more pronounced elevation of TPT in early compared to late-onset patients. Significant correlations between HRV and TPT were found among late-onset cases, indicating a possible relationship between loss of thin nerve fibers in somatic and autonomic nerves, while generally no such relationships were found among early-onset cases. This observation emphasizes the importance of testing both HRV and TPT to ensure optimal early detection of neuropathic changes in an as wide as possible range of small nerve fibers in suspected ATTR patients. This is of particular importance as the phenotype of the ATTR disease varies between groups with different age of onset.

Quantitative sensation and autonomic test abnormalities in transthyretin amyloidosis polyneuropathy

This study assesses the value of standard quantitative autonomic (QAT) and sensation (QST) tests in detecting, characterizing, and quantitating the severity of transthyretin amyloid polyneuropathy (TTR-A-PN). This information is needed for prospective therapeutic trials, epidemiologic surveys, and medical practice. We reviewed 36 patients with TTR-A-PN who were evaluated between 1997 and 2007. They had neurologic, genetic, electrodiagnostic, and autonomic reflex screen evaluations and allowed their medical records and test results to be evaluated for research purposes. Of these, 22 patients had also been tested by quantitative sensation tests (QSTs). The median symptom duration was 4 years (range 1-30 years). Among quantitative nerve tests evaluated, composite scores of nerve conduction (Sigma5 NC nds), a composite score of QSTs (Sigma3 QST nds), and quantitative autonomic tests (QSART, HR(db), and CASS) gave high frequencies of abnormality. The results show that peripheral autonomic and small-fiber sensory dysfunction was prominent and characteristic of most of the patients we studied. However, this involvement was not selective for small-diameter sensory and autonomic nerve fibers; large motor and sensory fibers were also shown to be dysfunctional. Dysfunction of large fibers was approximately as frequent as that of small fibers. This study provides a rationale for the use of QAT, QST, and Sigma5 NC nds as standard, objective, and quantitative measures for assessing the severity of TTR-A-PN in epidemiologic surveys, therapeutic trials, and medical practice.