Selective silencing of a mutant transthyretin allele by small interfering RNAs

Novel Therapies for Prevention and Early Treatment of Cardiomyopathies

Heritable cardiomyopathies are a class of heart diseases caused by variations in a number of genetic loci. Genetic variants on one allele lead to either a degraded protein, which causes a haploinsufficiency of that protein, or a nonfunctioning protein that subverts the molecular system within which the protein works. Over years, both of these mechanisms eventually lead to diseased heart tissue and symptoms of a failing heart. Most cardiomyopathy treatments repurpose heart failure drugs to manage these symptoms and avoid adverse outcomes. There are few therapies that correct the underlying pathogenic genetic or molecular mechanism. This review will reflect on this unmet clinical need in genetic cardiomyopathies and consider a variety of therapies that address the mechanism of disease rather than patient symptoms. These therapies are genetic, targeting a defective gene or transcript, or ameliorating a genetic insufficiency. However, there are also a number of small molecules under exploration that modulate downstream faulty protein products affected in cardiomyopathies.

Recent Advances in Oligonucleotide-Based Therapy for Transthyretin Amyloidosis: Clinical Impact and Future Prospects

Transthyretin (TTR) amyloidosis, also known as transthyretin-related familial amyloidotic polyneuropathy (ATTR-FAP), is a fatal hereditary systemic amyloidosis caused by mutant forms of TTR. Although conventional treatments for ATTR-FAP, such as liver transplantation (LT) and TTR tetramer stabilizer, reportedly halt the progression of clinical manifestation, these therapies have several limitations. Oligonucleotide-based therapy, e.g. small interfering RNA (siRNA)- and antisense oligonucleotides (ASOs)-based therapy, hold enormous potential for the treatment of intractable diseases such as ATTR-FAP, by specifically regulating the gene responsible for the disease. Clinical evidence strongly suggests that LT inhibits mutant TTR production, thus improving the manifestation of ATTR-FAP. Therefore, an oligonucleotide-based therapy for ATTR-FAP, which reduces the production of TTR by the liver, has recently been developed in preclinical and clinical studies. This review focuses on recent advances in oligonucleotide-based therapy and future prospects of next-generation oligonucleotide-based drugs for therapeutic use against ATTR-FAP.

Progression of transthyretin (TTR) amyloidosis in donors and recipients after domino liver transplantation-a prospective single-center cohort study

Liver transplantation (LT) is the first-line therapy in patients with transthyretin (TTR) amyloidosis and progressive familial amyloid polyneuropathy (FAP). Explanted organs from these patients can be used for domino liver transplantation (DLT). After DLT, de novo amyloidosis may develop in domino recipients (DR). Data were collected prospectively in a transplant database. Electroneurography by nerve conduction velocity (NCV), quantitative sensory testing, heart rate variability (HRV), sympathetic skin response, orthostatic reaction (tilt table test), transthoracic echocardiography, cardiac MRI and organ biopsy results were evaluated. The cohort included 24 FAP- (11 Val30Met, 13 nonVal30Met) and 23 DR-patients. DR symptoms referred to post-DLT only, while those of FAP patients were both pre- and post-transplantation. Symptoms of TTR-amyloidosis in Val30Met and Non-Val30Met patients pre- and post-LT were similarly distributed. Biopsy-proven de novo amyloidosis occurred in 4/23 DR after a mean observation of 10 years. Analysis for manifestations of amyloidosis only included patients with available 5-year follow-up data (n = 13 FAP, n = 12 DR). Compared to Val30Met FAP patients pre-LT, Val30Met DR patients had better NCV (P = 0.04) and HRV (P = 0.015). In the Non-Val30Met group no differences were found between DR and FAP patients pre-LT. TTR-amyloidosis symptoms showed no differences in FAP patients pre- and 5 years post-LT, irrespective of Val30Met status. In DR patients, de novo amyloidosis occurred earlier than expected. Therefore, recipients for DLT need to be carefully selected and followed.

Evaluation of Therapeutic Oligonucleotides for Familial Amyloid Polyneuropathy in Patient-Derived Hepatocyte-Like Cells

Familial amyloid polyneuropathy (FAP) is caused by mutations of the transthyretin (TTR) gene, predominantly expressed in the liver. Two compounds that knockdown TTR, comprising a small interfering RNA (siRNA; ALN-TTR-02) and an antisense oligonucleotide (ASO; IONIS-TTRRx), are currently being evaluated in clinical trials. Since primary hepatocytes from FAP patients are rarely available for molecular analysis and commercial tissue culture cells or animal models lack the patient-specific genetic background, this study uses primary cells derived from urine of FAP patients. Urine-derived cells were reprogrammed to induced pluripotent stem cells (iPSCs) with high efficiency. Hepatocyte-like cells (HLCs) showing typical hepatic marker expression were obtained from iPSCs of the FAP patients. TTR mRNA expression of FAP HLCs almost reached levels measured in human hepatocytes. To assess TTR knockdown, siTTR1 and TTR-ASO were introduced to HLCs. A significant downregulation (>80%) of TTR mRNA was induced in the HLCs by both oligonucleotides. TTR protein present in the cell culture supernatant of HLCs was similarly downregulated. Gene expression of other hepatic markers was not affected by the therapeutic oligonucleotides. Our data indicate that urine cells (UCs) after reprogramming and hepatic differentiation represent excellent primary human target cells to assess the efficacy and specificity of novel compounds.

Diagnosis, Prognosis, and Therapy of Transthyretin Amyloidosis

Transthyretin amyloidosis is a fatal disorder that is characterized primarily by progressive neuropathy and cardiomyopathy. It occurs in both a mutant form (with autosomal dominant inheritance) and a wild-type form (with predominant cardiac involvement). This article guides clinicians as to when the disease should be suspected, describes the appropriate diagnostic evaluation for those with known or suspected amyloidosis, and reviews the interventions currently available for affected patients.

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.

Novel strategies for the diagnosis and treatment of cardiac amyloidosis

Systemic amyloidoses are rare, complex diseases caused by misfolding of autologous protein. The presence of heart involvement is the most important prognostic determinant. The diagnosis of amyloid cardiac involvement relies on echocardiography and magnetic resonance imaging, while scintigraphy with bone tracers is helpful in differentiating light chain amyloidosis from other types of amyloidosis involving the heart. Although these diseases are fatal, effective treatments exist that can alter their natural history, provided that they are started before irreversible cardiac damage has occurred. Refined diagnostic techniques, accurate patients' stratification based on biomarkers of cardiac dysfunction, the availability of novel, more powerful drugs, and ultimately, the unveiling of the cellular mechanisms of cardiac damage created a favorable environment for a dramatic improvement in the treatment of this disease that we expect in the next few years.

The transthyretin amyloidoses: advances in therapy

There are two forms of transthyretin (TTR) amyloidosis: non-hereditary and hereditary. The non-hereditary form (ATTRwt) is caused by native or wild-type TTR and was previously referred to as senile systemic amyloidosis. The hereditary form (ATTRm) is caused by variant TTR which results from a genetic mutation of TTR. The predominant effect of ATTRwt amyloidosis is on the heart, with patients having a greater left ventricular wall thickness at presentation than the devastating form which is light chain (AL) amyloidosis. ATTRm amyloidosis is broadly split into two categories: a type that predominantly affects the nervous system (often called familial amyloid polyneuropathy (FAP)) and one with a predilection for the heart (often called familial amyloid cardiomyopathy (FAC)). Approximately half of all TTR mutations known to express a clinical phenotype cause a cardiomyopathy. Since the introduction of orthotopic liver transplantation for ATTRm amyloidosis in 1991, several additional therapies have been developed. These therapies aim to provide a reduction or elimination of TTR from the plasma (through genetic approaches), stabilisation of the TTR molecule (to prevent deposition) and dissolution of the amyloid matrix. We describe the latest developments in these approaches to management, many of which are also applicable to wild-type amyloidosis.

Recent progress in the understanding and treatment of transthyretin amyloidosis

WHAT IS KNOWN AND OBJECTIVE

Transthyretin (TTR) is a representative amyloidogenic protein in humans. Rate-limiting tetramer dissociation and rapid monomer misfolding and misassembly of variant TTR result in autosomal dominant familial amyloidosis. Analogous misfolding of wild-type TTR results in senile systemic amyloidosis (SSA) presenting as sporadic amyloid disease in the elderly. The objective of this review is to summarize recent progress in our understanding and treatment of TTR amyloidosis.

METHODS

Literature searches were conducted on the topics of transthyretin, familial amyloid polyneuropathy and clinical trials, using PubMed, the United States clinical trials directory, pharmaceutical company websites and news reports. The information was collected, evaluated for relevance and quality, critically assessed and summarized.

RESULTS AND DISCUSSION

The current standard first-line treatment of familial TTR amyloidosis is liver transplantation. However, large numbers of patients are not suitable transplant candidates. Recently, the clinical effects of TTR tetramer stabilizers, tafamidis and diflunisal, were demonstrated in randomized clinical trials, and tafamidis has been approved for the treatment of FAP in European countries and Japan. In addition, gene therapies with antisense oligonucleotides and small interfering RNAs are promising strategies to ameliorate TTR amyloidoses and are currently in clinical trials.

WHAT IS NEW AND CONCLUSIONS

Liver transplantation to treat the familial TTR amyloidosis will likely be replaced by other less invasive therapies, such as TTR tetramer stabilizers and possibly gene therapy approaches. These newly developed therapies are expected to be effective for not only familial TTR amyloidosis but also SSA, based on their mechanisms of action.

Recent advances in transthyretin amyloidosis therapy

Mutant (MT) forms of transthyretin (TTR) cause the most common type of autosomal-dominant hereditary systemic amyloidosis-familial amyloidotic polyneuropathy (FAP). Until 20 years ago, FAP was thought to be an endemic disease, but FAP is known to occur worldwide. To date, more than 130 mutations in the TTR gene have been reported. Genotype-phenotype correlations are seen in FAP, and some variation in clinical presentation is often observed in individual kindreds with the same mutation and even among family members. Of the pathogenic TTR mutations, Val30Met was the first to be identified and is the most frequent known mutation found throughout the world. Studies of patients with FAP amyloidogenic TTR (ATTR) Val30Met documented sensorimotor polyneuropathy, autonomic dysfunction, heart and kidney failure, gastrointestinal tract (GI) disorders, and other symptoms leading to death, usually within 10 years of the onset of disease. Diagnosis is sometimes delayed, especially in patients without a clear family history and typical clinical manifestations, since diagnosis requires various studies and techniques such as histopathology, genetic testing, and mass spectrometry. For treatment of FAP, liver transplantation (LT) reportedly halts the progression of clinical manifestations. Exchange of an FAP patient's diseased liver with a healthy liver causes MT TTR in the body to be replaced by wild-type (WT) TTR. Although clinical evaluations indicated that progression of other clinical symptoms such as peripheral neuropathy, GI symptoms, and renal involvement usually halted after LT in FAP ATTR Val30Met patients, recent studies suggested that LT failed to prevent progression of cardiac amyloidosis in FAP ATTR Val30Met patients after LT, with this failure reportedly being due to continued formation of amyloid that derived mainly from WT TTR secreted from the transplanted non-mutant liver graft. In recent years, many therapeutic strategies have been proposed, and several ongoing therapeutic trials involve, for example, stabilizers of TTR tetramers (tafamidis and diflunisal) and gene therapies to suppress TTR expression (antisense methods and use of small interfering RNAs). These novel therapies may prove to prevent progression of FAP.

Interleukin-1 signaling pathway as a therapeutic target in transthyretin amyloidosis

INTRODUCTION

Inflammation is a key pathological hallmark of several neurodegenerative disorders including Alzheimer's disease, Parkinson's disease and familial amyloidotic polyneuropathy (FAP). Among all inflammatory cytokines associated with FAP, IL-1β, in particular, has been implicated in playing a key pathogenic role. In the present study, we sought to investigate whether blocking IL-1β signaling provides disease-modifying benefits in an FAP mouse model.

METHODS

We assessed the effect of chronic administration of Anakinra, an IL-1 antagonist, on FAP pathogenesis in vivo, using real-time polymerase chain reaction (qPCR), semi-quantitative immunohistochemistry (SQ-IHC), western blot and nerve morphometric analyses.

RESULTS

We found that treatment with Anakinra prevents transthyretin (TTR) extracellular deposition in sciatic nerve, protecting unmyelinated nerve fibers from aggregate-induced degeneration. Moreover, Anakinra administration significantly suppressed IL-1 signaling pathway and inhibited apoptosis and nitrative stress.

CONCLUSIONS

The present work highlights the relevance of the IL-1 signaling pathway in the pathophysiology of FAP. Our results bring to light the importance of non-amyloid targets in the therapeutic strategies for this disorder. Thus, we propose the use of Anakinra as a potential therapeutic agent for TTR-related amyloidosis.

An overview of drugs currently under investigation for the treatment of transthyretin-related hereditary amyloidosis

INTRODUCTION

Transthyretin (TTR)-related hereditary amyloidosis is an adult-onset, dominantly inherited, systemic neurodegenerative disease endemic in some populations. Stabilization of the native structure of TTR by small-molecule ligands has recently proved effective in slowing neurological progression. Two drugs, tafamidis and diflunisal, are now available for most patients, particularly in the early stage of the disease. However, this disorder remains life threatening with several unmet needs. There are great expectations for a number of novel agents undergoing investigation.

AREAS COVERED

The authors review the current investigational drugs for the treatment of TTR amyloidosis according to the different steps of the fibrillogenesis process they target. Innovative approaches include suppression of TTR secretion, prevention of TTR misfolding by stronger stabilizers identified through structure-based design and high-throughput screening methodologies as well as the redirection of pathogenic aggregates toward nontoxic species and reabsorption of deposits through amyloid disrupters and immunotherapy.

EXPERT OPINION

Suppression of TTR synthesis by antisense oligonucleotides and small-interfering RNA is presently one of the most promising therapeutic approaches. However, well-designed clinical trials are required to establish their safety and efficacy compared with liver transplantation, tafamidis and diflunisal. With a longer time frame, it may be possible to develop combination therapies that target multiple steps of the aggregation process that could provide the best long-life effective treatments for this devastating disease.

Biodegradable lipids enabling rapidly eliminated lipid nanoparticles for systemic delivery of RNAi therapeutics

In recent years, RNA interference (RNAi) therapeutics, most notably with lipid nanoparticle-based delivery systems, have advanced into human clinical trials. The results from these early clinical trials suggest that lipid nanoparticles (LNPs), and the novel ionizable lipids that comprise them, will be important materials in this emerging field of medicine. A persistent theme in the use of materials for biomedical applications has been the incorporation of biodegradability as a means to improve biocompatibility and/or to facilitate elimination. Therefore, the aim of this work was to further advance the LNP platform through the development of novel, next-generation lipids that combine the excellent potency of the most advanced lipids currently available with biodegradable functionality. As a representative example of this novel class of biodegradable lipids, the lipid evaluated in this work displays rapid elimination from plasma and tissues, substantially improved tolerability in preclinical studies, while maintaining in vivo potency on par with that of the most advanced lipids currently available.

Disease-causing allele-specific silencing by RNA interference

Small double-stranded RNAs (dsRNAs) of approximately 21-nucleotides in size, referred to as small interfering RNA (siRNA) duplexes, can induce sequence-specific posttranscriptional gene silencing, or RNA interference (RNAi). Since chemically synthesized siRNA duplexes were found to induce RNAi in mammalian cells, RNAi has become a powerful reverse genetic tool for suppressing the expression of a gene of interest in mammals, including human, and its application has been expanding to various fields. Recent studies further suggest that synthetic siRNA duplexes have the potential for specifically inhibiting the expression of an allele of interest without suppressing the expression of other alleles, i.e., siRNA duplexes likely confer allele-specific silencing. Such gene silencing by RNAi is an advanced technique with very promising applications. In this review, I would like to discuss the potential utility of allele-specific silencing by RNAi as a therapeutic method for dominantly inherited diseases, and describe possible improvements in siRNA duplexes for enhancing their efficacy.

Impact of antibodies against amyloidogenic transthyretin (ATTR) on phenotypes of patients with familial amyloidotic polyneuropathy (FAP) ATTR Valine30Methionine

BACKGROUND

This study investigated whether a relationship exists between the presence of de novo antibodies and the clinical manifestations of familial amyloidotic polyneuropathy (FAP).

METHODS

Serum samples were collected from 25 Japanese and 6 Swedish FAP amyloidogenic transthyretin (ATTR) Valine30Methionine (V30M) patients, 4 asymptomatic Japanese ATTR V30M gene carriers, and 24 Japanese healthy volunteers. Study methods included enzyme-linked immunosorbent assay (ELISA) and mass spectrometry.

RESULTS

Three Japanese and 5 Swedish patients had significantly higher levels of antibodies against ATTR than did healthy volunteers and asymptomatic gene carriers (P<0.05). All 8 patients with higher antibody levels were late-onset cases. The ratio of wild-type TTR to ATTR V30M in serum from the high-antibody group was higher than that of the low-antibody group. ELISA results revealed two epitopes at positions 24-35 and 105-115 of ATTR V30M. We found a significant positive correlation between levels of the antibody at positions 24-35 and the age at FAP onset (r=0.751, P<0.05). An age-dependent increase in the occurrence of antibodies was observed in these patients with an epitope at positions 24-35.

CONCLUSIONS

These findings may help explain the differences in early- and late-onset FAP and/or the progression of FAP.

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.

AL amyloid imaging and therapy with a monoclonal antibody to a cryptic epitope on amyloid fibrils

The monoclonal antibody 2A4 binds an epitope derived from a cleavage site of serum amyloid protein A (sAA) containing a -Glu-Asp- amino acid pairing. In addition to its reactivity with sAA amyloid deposits, the antibody was also found to bind amyloid fibrils composed of immunoglobulin light chains. The antibody binds to synthetic fibrils and human light chain (AL) amyloid extracts with high affinity even in the presence of soluble light chain proteins. Immunohistochemistry with biotinylated 2A4 demonstrated positive reaction with ALκ and ALλ human amyloid deposits in various organs. Surface plasmon resonance analyses using synthetic AL fibrils as a substrate revealed that 2A4 bound with a K_D of ∼10 nM. Binding was inhibited in the presence of the –Glu-Asp- containing immunogen peptide. Radiolabeled 2A4 specifically localized with human AL amyloid extracts implanted in mice (amyloidomas) as evidenced by single photon emission (SPECT) imaging. Furthermore, co-localization of the radiolabeled mAb with amyloid was shown in biodistribution and micro-autoradiography studies. Treatment with 2A4 expedited regression of ALκ amyloidomas in mice, likely mediated by the action of macrophages and neutrophils, relative to animals that received a control antibody. These data indicate that the 2A4 mAb might be of interest for potential imaging and immunotherapy in patients with AL amyloidosis.

Amyloid neuropathies

Peripheral neuropathy is a common complication of many of the systemic amyloidoses. Although the cause of neuropathy is not entirely clear, it is likely related to amyloid deposition within the nerve. This may lead to focal, multifocal, or diffuse neuropathies involving sensory, motor and/or autonomic fibers. The presenting symptoms depend on the distribution of nerves affected. One of the most common phenotypes is sensorimotor polyneuropathy, which is characterized by symptoms of neuropathic pain, numbness, and in advanced cases weakness. Symptoms begin in the feet and ultimately progress to the proximal legs and hands. The most common focal neuropathy is a median neuropathy at the wrist, clinically known as carpal tunnel syndrome. Carpal tunnel symptoms may include pain and sensory disturbances in the lateral palm and fingers; hand weakness may ensue if the focal neuropathy is severe. Autonomic neuropathy may affect a variety of organ systems such as the cardiovascular, gastrointestinal, and genitourinary systems. Symptoms may be non-specific making the diagnosis of autonomic neuropathy more difficult to identify. However, it is important to recognize and distinguish autonomic neuropathy from diseases of the end-organs themselves. This article reviews the inherited and acquired amyloidoses that affect the peripheral nervous system including familial amyloid polyneuropathy, and primary, secondary and senile amyloidosis. We emphasize the clinical presentation of the neurologic aspects of these diseases, physical examination findings, appropriate diagnostic evaluation, treatment and prognosis.

Familial amyloidotic polyneuropathy: current and emerging treatment options for transthyretin-mediated amyloidosis

Transthyretin familial amyloid polyneuropathy (TTR-FAP) is a fatal clinical disorder characterized by extracellular deposition of abnormal fibrils derived from misfolded, normally soluble transthyretin (TTR) molecules. The disease is most commonly caused by a point mutation within the TTR gene inherited in an autosomal dominant fashion. Over 100 of such mutations have been identified, leading to destabilization of the physiological TTR tetramer. As a result, many monomers originate with a tendency for spontaneous conformational changes and self-aggregation. The main clinical feature of TTR-FAP is progressive sensorimotor and autonomic neuropathy. In the beginning, this polyneuropathy predominantly involves small unmyelinated nerve fibers with the result of dissociated sensory loss disproportionately affecting sensation of pain and temperature. Autonomic neuropathy typically accompanies sensory deficits early in the disease course. The symptoms include orthostatic hypotension, constipation alternating with diarrhea, erectile dysfunction, anhydrosis, and urinary retention or incontinence. Later, involvement of motor fibers causes rapidly progressive weakness and gait disturbances. In addition to the peripheral nervous system, the heart and the gut are frequently affected. Onset of symptoms is bimodal, with one peak at age 33 years (early onset) and another distinct peak in the sixth decade of life (late onset). The course of TTR-FAP is uniformly progressive and fatal. Death occurs an average of 10.8 years after the onset of symptoms in Portuguese patients, and 7.3 years in late-onset Japanese patients. Common causes include cachexia, cardiac failure, arrhythmia, and secondary infections. Liver transplantation is the standard therapy for patients who are in a clinical condition good enough to tolerate this intervention because it stops progression of neuropathy by removing the main source of mutant TTR. Recently, orally administered tafamidis meglumine has been approved by European authorities for treatment of FAP. The substance has been shown to stabilize the TTR tetramer, thereby improving the outcome of patients with TTR-FAP. Various other strategies have been studied in vitro to prevent TTR amyloidosis, including gene therapy, immunization, dissolution of TTR aggregates, and free radical scavengers, but none of them is ready for clinical use so far.

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.

How to manage primary amyloidosis

Immunoglobulin light chain amyloidosis is a protein deposition disorder where the precursor protein represents a monoclonal immunoglobulin light or heavy chain. Deposition in viscera results in restrictive cardiomyopathy, nephrotic range proteinuria, demyelinating peripheral neuropathy, hepatomegaly and malabsorption syndrome. Diagnosis requires biopsy with Congo red staining. Invasive biopsies are not required generally. It is essential that after a histologic diagnosis is obtained, the tissue is validated to have an immunoglobulin light chain composition so patients are spared unnecessary chemotherapy. The disease prognosis and patient monitoring are linked to serialized measurement of cardiac biomarkers and immunoglobulin-free light chains. Most patients require cytotoxic chemotherapy. For some patients, this therapy involves stem cell collection and myeloablative chemotherapy; for others, chemotherapy includes an alkylator and a corticosteroid; and for some, it involves addition of a novel agent in the form of an immunomodulatory drug or a proteasome inhibitor. Delays in diagnosis continue to be an obstacle to initiating effective therapy. Early mortality rates remain high. Effective chemotherapy can result in reversal of organ dysfunction and recovery. Reductions in light chain production translate to improved survival.

Inhibition of pathologic immunoglobulin-free light chain production by small interfering RNA molecules

OBJECTIVE

Morbidity and mortality occurring in patients with multiple myeloma, AL amyloidosis, and light chain deposition disease can result from the pathologic deposition of monoclonal immunoglobulin light chains (LCs) in kidneys and other organs. To reduce synthesis of such components, therapy for these disorders typically has involved antiplasma cell agents; however, this approach is not always effective and can have adverse consequences. We have investigated another means to achieve this objective; namely, RNA interference.

MATERIALS AND METHODS

SP2/O mouse myeloma cells were stably transfected with a construct encoding a λ6 LC (Wil) under control of the cytomegalovirus promoter, while λ2-producing myeloma cell line RPMI 8226 was purchased from the American Type Culture Collection (Manassas, VA, USA). Both were treated with small interfering RNA directed specifically to the V, J, or C portions of the molecules and then analyzed by enzyme-linked immunosorbent assay, flow cytometry, and real-time polymerase chain reaction.

RESULTS

Transfected cells were found to constitutively express detectable quantities of messenger RNA and protein Wil and, after exposure to small interfering RNAs, an ∼ 40% reduction in messenger RNA and LC production was evidenced at 48 hours. An even greater effect was seen with the 8226 cells.

CONCLUSIONS

Our results have shown that RNA interference can markedly reduce LC synthesis and provide the basis for testing the therapeutic potential of this strategy using in vivo experimental models of multiple myeloma.