Quantitative 99mTc-pyrophosphate Myocardial Uptake: Changes on Transthyretin Stabilization Therapy.

BACKGROUND: Quantitative technetium-99m-pyrophosphate cardiac single photon emission computed tomography (99mTc-PYP SPECT/CT) is an emerging method for estimating myocardial burden of transthyretin cardiac amyloidosis (ATTR-CA), but its efficacy in monitoring longitudinal changes remains uncertain. We aimed to investigate longitudinal changes in cardiac ATTR amyloid burden following transthyretin stabilization therapy using visual and quantitative 99mTc-PYP SPECT/CT and to relate these with changes in cardiac biomarkers and function. METHODS: This prospective longitudinal cohort study investigated changes in 99mTc-PYP SPECT/CT in 23 participants with ATTR-CA on transthyretin stabilization therapy (median 2.6 years). Quantitative analysis included left ventricular (LV) standardized uptake values (SUVmax, SUVmean), cardiac amyloid activity (CAA; SUVmean*LV activity volume), and percent injected dose (%ID) (mean activity concentration*LV activity volume/injected activity), calculated using a threshold of >1.5 times left atrial blood pool activity concentration on SPECT/CT. Longitudinal changes of paired continuous and ordinal variables were analyzed using Wilcoxon signed-rank test. RESULTS: Following therapy, visual grade decreased significantly (p=0.003). Several quantitative 99mTc-PYP metrics also decreased significantly: SUVmax (median -0.75, p=0.011), CAA (median -406.6, p<0.001), and %ID (median -0.45, p<0.001). Serum transthyretin levels improved (median +6.5 mg/dL, p=0.008). Echocardiographic parameters (global longitudinal strain, LV mass index, LV wall thickness), N-terminal pro-B-type natriuretic peptide, and estimated glomerular filtration rate remained stable. CONCLUSION: Favorable changes in 99mTc-PYP myocardial uptake were observed in participants on transthyretin stabilization therapy, while echocardiographic parameters and biomarkers remained stable. These results likely signify myocardial ATTR amyloid stabilization rather than amyloid burden regression. Further investigation is needed to understand the implications of these findings.

Recent Advances in Positron Emission Tomography Radiotracers to Image Cardiac Amyloidosis.

Cardiac amyloidosis includes a group of protein-misfolding diseases characterized by fibril accumulation within the extracellular space of the myocardium and cardiac dysfunction. Cardiac amyloidosis has high mortality. Emerging radionuclide techniques have helped us to better understand disease pathogenesis, prognostication, and treatment response in cardiac amyloidosis. PURPOSE OF REVIEW: To review recent advances in molecular imaging of cardiac amyloidosis using amyloid PET radiotracers. RECENT FINDINGS: Multiple single center studies have shown that amyloid PET radiotracers allow definitive diagnosis and quantification of cardiac amyloid burden. These amyloid targeting tracers may provide means to improve early disease detection, risk stratification and treatment monitoring. Amyloid PET imaging may inform definitive imaging-based diagnosis for therapeutic decisions, risk stratification, and treatment monitoring. More research in unselected cohorts of patients with suspected cardiac amyloidosis is needed to optimize the clinical implementation of amyloid PET imaging.

Cardiac magnetic resonance biomarkers as surrogate endpoints in cardiovascular trials for myocardial diseases.

Cardiac magnetic resonance offers multiple facets in the diagnosis, risk stratification, and management of patients with myocardial diseases. Particularly, its feature to precisely monitor disease activity lends itself to quantify response to novel therapeutics. This review critically appraises the value of cardiac magnetic resonance imaging biomarkers as surrogate endpoints for prospective clinical trials. The primary focus is to comprehensively outline the value of established cardiac magnetic resonance parameters in myocardial diseases. These include heart failure, cardiac amyloidosis, iron overload cardiomyopathy, hypertrophic cardiomyopathy, cardio-oncology, and inflammatory cardiomyopathies like myocarditis and sarcoidosis.

99mTc Bone-Avid Tracer Cardiac Scintigraphy: Role in Noninvasive Diagnosis of Transthyretin Cardiac Amyloidosis.

Transthyretin cardiac amyloidosis (ATTR-CA) is an overlooked cause of heart failure, with substantial morbidity and mortality. The emergence of several novel therapies has fueled the interest in early and accurate diagnosis of ATTR-CA so that potentially life-saving pharmacologic therapy can be administered in a timely manner. The most promising imaging modality and biomarker is SPECT imaging with technetium 99m (99mTc)-radiolabeled bone-seeking tracers, which have high specificity in the diagnosis of ATTR-CA, potentially obviating biopsy. In this article, the authors provide a focused review on the use of 99mTc pyrophosphate (PYP), 3,3-diphosphono-1,2-propanodicarboxylic acid (DPD), and hydroxymethylene diphosphonate (HMDP) for diagnosis of ATTR-CA, present a systematic approach to interpretation of the scans, and highlight several common pitfalls to illustrate important diagnostic principles for accurate interpretation of these images. The authors indicate when to use endomyocardial biopsy for the diagnosis of cardiac amyloidosis and conclude with a section on quantitation of 99mTc-PYP/DPD/HMDP imaging.

Multimodality Imaging in Cardiac Amyloidosis.

PURPOSE OF REVIEW: Cardiac amyloidosis is an increasingly recognized condition with a growing range of targeted therapies, but diagnosis requires a high index of suspicion and multimodality imaging expertise. Early diagnosis remains key to improving quality of life and survival. This article reviews the multimodality imaging approach to the diagnosis, differentiation, and prognosis of cardiac amyloidosis. RECENT FINDINGS: Recent advances in multimodality cardiac imaging have allowed for earlier diagnosis of cardiac amyloidosis resulting in earlier initiation of life-saving therapy in cases of light chain amyloidosis and life-prolonging therapy in transthyretin amyloidosis. With these advances in multimodality imaging, it is important for cardiologists and cardiac imagers to be aware of the subtleties of early disease, the appropriate diagnostic approach as well as understanding the practicalities and pitfalls that are encountered with each modality.

Current and Evolving Multimodality Cardiac Imaging in Managing Transthyretin Amyloid Cardiomyopathy.

Amyloid transthyretin (ATTR) amyloidosis is a protein-misfolding disease characterized by fibril accumulation in the extracellular space that can result in local tissue disruption and organ dysfunction. Cardiac involvement drives morbidity and mortality, and the heart is the major organ affected by ATTR amyloidosis. Multimodality cardiac imaging (ie, echocardiography, scintigraphy, and cardiac magnetic resonance) allows accurate diagnosis of ATTR cardiomyopathy (ATTR-CM), and this is of particular importance because ATTR-targeting therapies have become available and probably exert their greatest benefit at earlier disease stages. Apart from establishing the diagnosis, multimodality cardiac imaging may help to better understand pathogenesis, predict prognosis, and monitor treatment response. The aim of this review is to give an update on contemporary and evolving cardiac imaging methods and their role in diagnosing and managing ATTR-CM. Further, an outlook is presented on how artificial intelligence in cardiac imaging may improve future clinical decision making and patient management in the setting of ATTR-CM.

Myocardial Characteristics, Cardiac Structure, and Cardiac Function in Systemic Light-Chain Amyloidosis.

BACKGROUND: In systemic light-chain (AL) amyloidosis, cardiac involvement portends poor outcomes. OBJECTIVES: The authors' objectives were to detect early myocardial alterations, to analyze longitudinal changes with therapy, and to predict major adverse cardiac events (MACE) in participants with AL amyloidosis using cardiac magnetic resonance imaging (MRI). METHODS: Recently diagnosed participants were prospectively enrolled. AL amyloidosis with and without cardiomyopathy (AL-CMP, AL-non-CMP) were defined based on abnormal cardiac biomarkers and wall thickness. MRI was performed at baseline, 6 months in all participants, and 12 months in participants with AL-CMP. MACE were defined as all-cause death, heart failure hospitalization, and cardiac transplantation. Mayo stage was based on troponin T, N-terminal pro-B-type natriuretic peptide, and difference in free light chains. RESULTS: This study included 80 participants (median age 62 years, 58% men). Extracellular volume (ECV) was abnormal (>32%) in all participants with AL-CMP and in 47% of those with AL-non-CMP. ECV tended to increase at 6 months (median +2%; AL-CMP P = 0.120; AL-non-CMP P = 0.018) and returned to baseline values at 12 months in participants with AL-CMP. Global longitudinal strain (GLS) improved at 6 months (median -0.6%; P = 0.048) and 12 months (median -1.2%; P < 0.001) in participants with AL-CMP. ECV and GLS were strongly associated with MACE (P < 0.001) and improved the prognostic value when added to Mayo stage (P ≤ 0.002). No participant with ECV ≤32% had MACE, while 74% of those with ECV >48% had MACE. CONCLUSIONS: In patients with systemic AL amyloidosis, ECV detects subclinical myocardial alterations. With therapy, ECV tends to increase at 6 months and returns to values unchanged from baseline at 12 months, whereas GLS improves at 6 and 12 months in participants with AL-CMP. ECV and GLS offer additional prognostic performance over Mayo stage. (Molecular Imaging of Primary Amyloid Cardiomyopathy [MICA]; NCT02641145).

Mechanisms of left ventricular systolic dysfunction in light chain amyloidosis: a multiparametric cardiac MRI study.

Background: Cardiac systolic dysfunction is a poor prognostic marker in light-chain (AL) cardiomyopathy, a primary interstitial disorder; however, its pathogenesis is poorly understood. Purpose: This study aims to analyze the effects of extracellular volume (ECV) expansion, a surrogate marker of amyloid burden on myocardial blood flow (MBF), myocardial work efficiency (MWE), and left ventricular (LV) systolic dysfunction in AL amyloidosis. Methods: Subjects with biopsy-proven AL amyloidosis were prospectively enrolled (April 2016-June 2021; Clinicaltrials.gov ID NCT02641145) and underwent cardiac magnetic resonance imaging (MRI) to quantify rest MBF by perfusion imaging, LV ejection fraction (LVEF) by cine MRI, and ECV by pre- and post-contrast T1 mapping. The MWE was estimated as external cardiac work from the stroke volume and mean arterial pressure normalized to the LV myocardial mass. Results: Rest MBF in 92 subjects (62 ± 8 years, 52 men) with AL amyloidosis averaged 0.87 ± 0.21 ml/min/g and correlated with MWE (r = 0.42; p < 0.001). Rest MBF was similarly low in subjects with sustained hematologic remission after successful AL amyloidosis therapy (n = 21), as in those with recently diagnosed AL amyloidosis. Both MBF and MWE decreased by ECV tertile (p < 0.01 for linear trends). The association of ECV with MWE comprised a direct effect (84% of the total effect; p < 0.001) on MWE from adverse interstitial remodeling assessed by ECV and an indirect effect (16% of the total effect; p < 0.001) mediated by MBF. There was a significant base-to-apex gradient of rest MBF in subjects with higher amyloid burden. Conclusions: In AL amyloidosis, both MBF and MWE decrease as cardiac amyloid burden and ECV expansion increase. Both structural and vascular changes from ECV expansion and myocardial amyloid burden appear to contribute to lower MWE.

Quantification of right ventricular amyloid burden with 18F-florbetapir positron emission tomography/computed tomography and its association with right ventricular dysfunction and outcomes in light-chain amyloidosis.

AIMS: In systemic light-chain (AL) amyloidosis, quantification of right ventricular (RV) amyloid burden has been limited and the pathogenesis of RV dysfunction is poorly understood. Using 18F-florbetapir positron emission tomography/computed tomography (PET/CT), we aimed to quantify RV amyloid; correlate RV amyloid with RV structure and function; determine the independent contributions of RV, left ventricular (LV), and lung amyloid to RV function; and associate RV amyloid with major adverse cardiac events (MACE: death, heart failure hospitalization, cardiac transplantation). METHODS AND RESULTS: We prospectively enrolled 106 participants with AL amyloidosis (median age 62 years, 55% males) who underwent 18F-florbetapir PET/CT, magnetic resonance imaging, and echocardiography. 18F-florbetapir PET/CT identified RV amyloid in 63% of those with and 40% of those without cardiac involvement by conventional criteria. RV amyloid burden correlated with RV ejection fraction (EF), RV free wall longitudinal strain (FWLS), RV wall thickness, RV mass index, N-terminal pro-brain natriuretic peptide, troponin T, LV amyloid, and lung amyloid (each P < 0.001). In multivariable analysis, RV amyloid burden, but not LV or lung amyloid burden, predicted RV dysfunction (EF P = 0.014; FWLS P < 0.001). During a median follow-up of 28 months, RV amyloid burden predicted MACE (P < 0.001). CONCLUSION: This study shows for the first time that 18F-florbetapir PET/CT identifies early RV amyloid in systemic AL amyloidosis prior to alterations in RV structure and function. Increasing RV amyloid on 18F-florbetapir PET/CT is associated with worse RV structure and function, predicts RV dysfunction, and predicts MACE. These results imply a central role for RV amyloid in the pathogenesis of RV dysfunction.

Prognostic Value of Left Ventricular 18F-Florbetapir Uptake in Systemic Light-Chain Amyloidosis.

BACKGROUND: Positron emission tomography/computed tomography (PET/CT) with 18F-florbetapir, a novel amyloid-targeting radiotracer, can quantify left ventricular (LV) amyloid burden in systemic light-chain (AL) amyloidosis. However, its prognostic value is not known. OBJECTIVES: The authors' aim was to evaluate the prognostic value of LV amyloid burden quantified by 18F-florbetapir PET/CT, and to identify mechanistic pathways mediating its association with outcomes. METHODS: A total of 81 participants with newly diagnosed AL amyloidosis underwent 18F-florbetapir PET/CT imaging. Amyloid burden was quantified using 18F-florbetapir LV uptake as percent injected dose. The Mayo stage for AL amyloidosis was determined using troponin T, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and free light chain levels. Major adverse cardiac events (MACE) were defined as all-cause death, heart failure hospitalization, or cardiac transplantation within 12 months. RESULTS: Among participants (median age, 61 years; 57% males), 36% experienced MACE, increasing from 7% to 63% across tertiles of LV amyloid burden (P < 0.001). LV amyloid burden was associated with MACE (HR: 1.46; 95% CI: 1.16-1.83; P = 0.001). However, this association became nonsignificant when adjusted for Mayo stage. In mediation analysis, the association between LV amyloid burden and MACE was mediated by NT-proBNP (P < 0.001), a marker of cardiomyocyte stretch and heart failure, and a component of Mayo stage. CONCLUSIONS: In this first study to link cardiac 18F-florbetapir uptake to subsequent outcomes, LV amyloid burden estimated by percent injected dose predicted MACE in AL amyloidosis. This effect was not independent of Mayo stage and was mediated primarily through NT-proBNP. These findings provide novel insights into the mechanism linking myocardial amyloid deposits to MACE.

Cardiac Amyloid Quantification Using 124I-Evuzamitide (124I-P5+14) Versus 18F-Florbetapir: A Pilot PET/CT Study.

BACKGROUND: Cardiac amyloid quantification could advance early diagnosis of amyloid cardiomyopathy (CMP) and treatment monitoring. However, current imaging tools are based on indirect measurements. 124I-evuzamitide is a novel pan-amyloid radiotracer binding to amyloid deposits from multiple amyloidogenic proteins. Its ability to quantify cardiac amyloid has not yet been investigated. OBJECTIVES: The objectives of this pilot study were to quantify myocardial 124I-evuzamitide uptake and to compare its diagnostic value to 18F-florbetapir in participants with amyloid CMP and control subjects. METHODS: This study included 46 participants: 12 with light-chain (AL) CMP, 12 with wild-type transthyretin (ATTRwt) CMP, 2 with hereditary amyloidosis, and 20 control subjects. All amyloidosis participants underwent positron emission tomography/computed tomography with 124I-evuzamitide and 18F-florbetapir. Control subjects underwent 124I-evuzamitide (n = 10) or 18F-florbetapir (n = 8) positron emission tomography/computed tomography. Left ventricular percent injected dose (LV% ID) was measured as mean activity concentration × myocardial volume/injected activity. High LV %ID was defined using Youden's index. RESULTS: In CMP participants, median age was 74 years and 92% were men. 124I-evuzamitide LV %ID differed across groups: median AL-CMP 1.48 (IQR: 1.12-1.89), ATTRwt-CMP 2.12 (IQR: 1.66-2.47), and control subjects 0.00 (IQR: 0.00-0.01; overall P < 0.001). High LV %ID perfectly discriminated CMP from control subjects. Discrimination performance was similar for 18F-florbetapir LV %ID. Notably, for ATTRwt-CMP, LV %ID was higher with 124I-evuzamitide than 18F-florbetapir (P = 0.002). 124I-evuzamitide LV %ID was correlated with interventricular septum thickness (Spearman's ρ = 0.78) and LV global longitudinal strain (ρ = 0.54) from echocardiography, and with LV mass index (ρ = 0.82) and extracellular volume (ρ = 0.51) from cardiac magnetic resonance. CONCLUSIONS: 124I-evuzamitide demonstrates uptake by cardiac amyloid and accurately discriminates amyloid CMP from control subjects. In AL-CMP, discrimination performance is similar to 18F-florbetapir. In ATTRwt-CMP, performance may be better with 124I-evuzamitide. Moderate-to-strong correlations of 124I-evuzamitide uptake with cardiac structural and functional metrics suggest valid amyloid quantification. Hence, 124I-evuzamitide is a promising novel radiotracer to detect and quantify cardiac amyloid.

Myocardial Characterization for Early Diagnosis, Treatment Response Monitoring, and Risk Assessment in Systemic Light-Chain Amyloidosis.

Aims: In systemic light-chain (AL) amyloidosis, cardiac involvement portends poor prognosis. Using myocardial characteristics on magnetic resonance imaging (MRI), this study aimed to detect early myocardial alterations, to analyze temporal changes with plasma cell therapy, and to predict risk of major adverse cardiac events (MACE) in AL amyloidosis. Methods and Results: Participants with recently diagnosed AL amyloidosis were prospectively enrolled. Presence of AL cardiomyopathy (AL-CMP vs. AL-non-CMP) was determined by abnormal cardiac biomarkers. MRI was performed at baseline and 6 months, with 12-month imaging in AL-CMP cohort. MACE was defined as all-cause death, heart failure hospitalization, or cardiac transplantation. Mayo AL stage was based on troponin T, NT-proBNP, and difference in free light chains. The study cohort included 80 participants (median age 62 years, 58% males). Median left ventricular extracellular volume (ECV) was significantly higher in AL-CMP (53% vs. 30%, p<0.001). ECV was abnormal (>32%) in all AL-CMP and in 47% of AL-non-CMP. ECV tended to increase at 6 months and decreased significantly from 6 to 12 months in AL-CMP (median -3%, p=0.011). ECV was strongly associated with MACE (p<0.001), and improved MACE prediction when added to Mayo AL stage (p=0.002). ECV≤32% identified a cohort without MACE, while ECV>48% identified a cohort with 74% MACE. Conclusions: In AL amyloidosis, ECV detects subclinical cardiomyopathy. ECV tends to increase from baseline to 6 months and decreases significantly from 6 and 12 months of plasma cell therapy in AL-CMP. ECV provides excellent risk stratification and offers additional prognostic performance over Mayo AL stage.

Modeling the Cost and Health Impacts of Diagnostic Strategies in Patients with Suspected Transthyretin Cardiac Amyloidosis.

Background Transthyretin cardiac amyloidosis (ATTR-CMP) is an increasingly recognized and treatable cause of heart failure with preserved ejection fraction. Multimodality cardiac imaging is recommended for ATTR-CMP diagnosis, but its cost-effectiveness in current clinical practice has not been well studied. Methods and Results Using a microsimulation model, we compared the cost-effectiveness of a combination of strategies involving 99mtechnetium pyrophosphate (PYP), cardiac magnetic resonance imaging, and endomyocardial biopsy for the diagnosis of ATTR-CMP. We developed a decision analytic model to project health care costs and lifetime quality-adjusted life years for symptomatic, older patients who present with congestive heart failure, with an increased left ventricular wall thickness and a 13% prevalence of ATTR-CMP. Rates of clinical events, costs, and quality-of-life values were estimated from published literature. The analysis was conducted from a US health care system perspective with health and cost outcomes discounted annually at 3%. In the base-case scenario, using a fixed tafamidis price of $16 000 annually (previously identified cost-effective price), total health care costs per person were lowest for the PYP-only strategy ($209 415) and highest for endomyocardial biopsy strategy ($215 881). Of the 7 strategies examined, the PYP-only strategy had the highest net monetary benefit using a willingness-to-pay threshold of $100 000/quality-adjusted life year. Results were sensitive to variations in model inputs for PYP and cardiac magnetic resonance imaging specificity, cost of tafamidis, and willingness-to-pay thresholds. Conclusions Our model-based analyses showed that a PYP-only strategy to diagnose ATTR-CMP is the most cost-effective strategy, at willingness-to-pay threshold of $100 000/quality-adjusted life year. At higher threshold ($150 000/quality-adjusted life year), sequential tests involving PYP and cardiac magnetic resonance imaging may be considered cost effective.

Effect of tafamidis on global longitudinal strain and myocardial work in transthyretin cardiac amyloidosis.

AIMS: In patients with transthyretin amyloid cardiomyopathy (ATTR-CM), the effect of tafamidis on myocardial function using serial speckle tracking echocardiography has not been reported. The purpose of this study was to describe the natural history of myocardial function in untreated ATTR-CM and determine the effect of tafamidis on myocardial functional parameters over 12 months of treatment. METHODS AND RESULTS: A total of 45 subjects with ATTR-CM were retrospectively studied: 23 treated with tafamidis and 22 untreated. Two-dimensional speckle tracking echocardiography was analysed at baseline and 1 year. Serial longitudinal, circumferential, and radial strain, twist, torsion, and myocardial work were measured. Over 1 year, absolute global longitudinal strain (GLS) deteriorated more in the untreated group by a median of 1.1% [inter-quartile range (IQR) 0.95] compared with 0.3% (IQR 1) in the tafamidis group (P = 0.02). Myocardial work index and efficiency also deteriorated to a greater degree: 142.5 mmHg% (IQR 197) and 4% (IQR 8), respectively, in the untreated group compared with 61.5 mmHg% (IQR 210) and 1% (IQR 7) in the tafamidis group (P = 0.04). There were no significant between group differences in left ventricular ejection fraction (LVEF), tissue Doppler velocities, circumferential or radial strain, LV twist or torsion at 1 year. The stabilization effect of tafamidis on myocardial function at 1 year did not differ according to baseline GLS, LVEF, or National Amyloidosis Centre disease stage. CONCLUSIONS: In ATTR-CM, tafamidis resulted in a lesser deterioration in GLS, myocardial work index, and efficiency over a 12-month period compared with a cohort not treated with tafamidis.

Myocardial Composition in Light-Chain Cardiac Amyloidosis More Than 1 Year After Successful Therapy.

OBJECTIVES: The goals of this study were to characterize myocardial composition during the active and remission phases of light-chain (AL) cardiac amyloidosis. BACKGROUND: Cardiac dysfunction in AL amyloidosis is characterized by dual insults to the myocardium from infiltration and toxicity from light chains during the active phase and by infiltration alone in the remission phase. METHODS: Prospectively enrolled subjects with cardiac AL amyloidosis (21 remission AL amyloidosis; age: 63.4 ± 7.3 years; 47.6% male; and 48 active AL amyloidosis; age: 62.5 ± 7.4 years; 60.4% male) underwent contrast-enhanced cardiac magnetic resonance with T1 and T2 mapping and measurement of extracellular volume (ECV). By definition, serum free light-chain levels were normal for at least 1 year following successful AL therapy in the remission group and abnormal in the active group. RESULTS: Myocardial ECV was similarly expanded in the remission and active AL amyloidosis groups (0.488 ± 0.082 vs 0.519 ± 0.083, respectively; P = 0.15). However, myocardial T2 relaxation times (47.7 ± 3.2 ms vs 45.5 ± 3.0 ms; P = 0.008) as well as native T1 times (1,368 ms [IQR: 1,290-1,422 ms] vs 1,264 ms [IQR: 1,203-1,380 ms]; P = 0.024) were significantly higher in the remission compared to the active AL amyloidosis group. CONCLUSIONS: Myocardial ECV is substantially expanded in the active AL and remission AL cardiac amyloidosis groups, but native T1 values were higher, suggesting a different myocardial composition. There is no evidence of myocardial edema in active AL cardiac amyloidosis. Future phenotyping studies of AL cardiac amyloidosis need to consider complementary myocardial markers that define the interstitial milieu in addition to changes in extracellular volume. (Molecular Imaging of Primary Amyloid Cardiomyopathy; NCT02641145).

A novel substitution of proline (P32L) destabilises ß2-microglobulin inducing hereditary systemic amyloidosis.

BACKGROUND: ß2-microglobulin amyloidosis was first described in the 1980s as a protein deposition disease associated with long-term haemodialysis. More recently, two inherited forms resulting from separate point mutations in the ß2-microglobulin gene have been identified. In this report, we detail a novel ß2M variant, P32L, caused by a unique dinucleotide mutation that is linked to systemic hereditary ß2-microglobulin amyloidosis. METHODS: Three family members from a Portuguese kinship featured cardiomyopathy, requiring organ transplantation in one case, along with soft tissue involvement; other involvements included gastrointestinal, neuropathic and sicca syndrome. In vitro studies with recombinant P32L, P32G, D76N and wild-type ß2-microglobulin were undertaken to compare the biophysical properties of the proteins. RESULTS: The P32L variant was caused by the unique heterozygous dinucleotide mutation c.154_155delinsTT. Amyloid disease featured lowered serum ß2-microglobulin levels with near equal amounts of circulating P32L and wild-type proteins; amyloid deposits were composed exclusively of P32L variant protein. In vitro studies of P32L demonstrated thermodynamic and chemical instability and enhanced susceptibility to proteolysis with rapid formation of pre-fibrillar oligomeric structures by N- and C-terminally truncated species under physiological conditions. CONCLUSIONS: This work provides both clinical and experimental evidence supporting the critical role of P32 residue replacement in ß2M amyloid fibrillogenesis.