Diagnosing amyloidosis

Utility of abdominal skin punch biopsy for detecting systemic amyloidosis

BACKGROUND

Early and accurate diagnosis of systemic amyloidosis (SA) is critical for optimal patient outcomes. Biopsy of clinically uninvolved skin and subcutaneous tissue including abdominal skin punch biopsy (ASPB) is often used as a surrogate for affected organ sampling. There is a lack of published data on the sensitivity and specificity of ASPB for diagnosing SA.

METHODS

Retrospective chart review between 2000 and 2020 of all ASPB was performed to diagnose SA. Amyloid deposition was confirmed by Congo red stain. Study group includes patients with histopathologically and clinically confirmed diagnosis of SA. Control group includes patients without histopathology of amyloid deposition and no clinical SA.

RESULTS

Forty-one patients meeting inclusion criteria were analyzed; 23 study group and 18 control group patients. The overall diagnostic sensitivity of ASPB was 43% (95% CI 23%-66%) and the specificity 100% (95% CI 81%-100%). The AL amyloidosis diagnostic sensitivity was 64% (95% CI 35%-87%). ASPB >10 mm in depth had 100% (95% CI 54%-100%) sensitivity compared to 24% for depth ≤10 mm (P = .002).

CONCLUSIONS

ASPB is a minimally invasive and highly specific method of diagnosing SA. It is particularly sensitive for diagnosing AL amyloidosis and the diagnostic sensitivity can be significantly improved with adequate biopsy depth and diameter.

Recommendations for the diagnosis and management of transthyretin amyloidosis with gastrointestinal manifestations

Transthyretin amyloid (ATTR) amyloidosis is an adult-onset, rare systemic disorder characterized by the accumulation of misfolded fibrils in the body, including the peripheral nerves, the heart and the gastrointestinal tract. Gastrointestinal manifestations are common in hereditary (ATTRv) amyloidosis and are present even before the onset of the polyneuropathy in some cases. Delays in diagnosis of ATTRv amyloidosis with gastrointestinal manifestations commonly occur because of fragmented knowledge among gastroenterologists and general practitioners, as well as a shortage of centers of excellence and specialists dedicated to disease management. Although the disease is becoming well-recognized in the societies of Neurology and Cardiology, it is still unknown for most gastroenterologists. This review presents the recommendations for ATTRv amyloidosis with gastrointestinal manifestations elaborated by a working group of European gastroenterologists and neurologists, and aims to provide digestive health specialists with an overview of crucial aspects of ATTRv amyloidosis diagnosis to help facilitate rapid and accurate identification of the disease by focusing on disease presentation, misdiagnosis and management of gastrointestinal symptoms.

hATTR Pathology: Nerve Biopsy Results from Italian Referral Centers

Pathological evidence of amyloid on nerve biopsy has been the gold standard for diagnosis in hereditary transthyretin amyloidosis polyneuropathy (hATTR-PN) for a long time. In this article, we reviewed the pathological findings of a large series of sural nerve biopsies from a cohort of hATTR-PN patients, collected by different Italian referral centers. Patients and Methods: We reviewed clinical and pathological data from hATTR-PN patients, diagnosed and followed in five Italian referral centers for peripheral neuropathies. Diagnosis was formulated after a positive genetic test for transthyretin (TTR) mutations. Sural nerve biopsy was performed according to standard protocols. Results: Sixty-nine sural nerve biopsies from hATTR-PN patients were examined. Congo red positive deposits were found in 73% of cases. Only the Phe64Leu mutation failed to show amyloid deposits in a high percentage of biopsies (54%), as already described. Unusual pathological findings, such as myelin abnormalities or inflammatory infiltrates, were detected in occasional cases. Conclusions: Even if no longer indicated to confirm hATTR-PN clinical suspicion, nerve biopsy remains, in expert hands, a rapid and inexpensive tool to detect amyloid deposition. In Italy, clinicians should be aware that a negative biopsy does not exclude hATTR-PN, particularly for Phe64Leu, one of the most frequent mutations in this country.

Abdominal fat pad biopsies exhibit good diagnostic accuracy in patients with suspected transthyretin amyloidosis

Background

The diagnostic accuracy of histopathological detection of transthyretin amyloid (ATTR) by Congo red staining of abdominal fat samples has been questioned since low sensitivity has been reported, especially for patients with ATTR cardiomyopathy. However, the outcome of surgically obtained fat pad biopsies has not yet been evaluated. The aim was to evaluate the diagnostic accuracy of skin punch biopsies from abdominal fat in patients with suspected ATTR amyloidosis.

Material and methods

Data were evaluated from patients who had undergone abdominal fat pad biopsies using a skin punch due to suspected amyloidosis from 2006 to 2015. The biopsies had been analysed using Congo red staining to determine the presence of amyloid, and immunohistochemistry or Western blot to determine the type of amyloidosis. The final diagnosis was based on the clinical picture, biopsy results and DNA sequencing. Minimum follow-up after the initial biopsy was 3 years.

Results

Two hundred seventy-four patients (61% males) were identified, and in 132 (48%), a final diagnosis of amyloidosis had been settled. The majority (93%) had been diagnosed with hereditary transthyretin (ATTRv) amyloidosis, and therefore subsequent analyses were focused on these patients. Overall, our data showed a test specificity of 99% and a sensitivity of 91%. Ninety-eight (94%) of the patients had neuropathic symptoms at diagnosis, whereas 57 (55%) had signs of amyloid cardiomyopathy. Subgroup analyses showed that patients with merely neuropathic symptoms displayed the highest test sensitivity of 91%, whereas patients with pure cardiomyopathy displayed the lowest sensitivity of 83%. However, no significant differences in sensitivity were found between patients with or without cardiomyopathy or between the sexes.

Conclusions

Abdominal fat pad biopsies exhibit good diagnostic accuracy in patients with suspect ATTRv amyloidosis, including patients presenting with cardiomyopathy. In addition, the method enables typing not only of the precursor protein but also of the amyloid fibril type, which is related to the phenotype and to the outcome of the disease.

Updates in processing of anterior fat pad aspirate for amyloid (with video and sketches)

Fat pad aspiration is a commonly used method for detecting amyloid in tissue. Amyloid is detected in the small blood vessels of the aspirated adipose tissue. Optimum evaluation of amyloid with electron microscopy requires at least 15 blood vessels in the fat pad aspirate. The presence of a significant proportion of adipocytes in the aspirate dilutes the fibrovascular portion. This may compromise the evaluation for amyloid with electron microscopy and in FFPE with proteomic studies by mass spectroscopy for confirmation of the amyloid subtype. This video article describes the updated protocol for processing the anterior fat pad aspirate. It demonstrates how to remove the interference of blood and fatty component in the fat pad aspirate performed by the previously reported procedure.

Diagnosis and Treatment of Hereditary Transthyretin Amyloidosis (hATTR) Polyneuropathy: Current Perspectives on Improving Patient Care

Hereditary transthyretin amyloidosis (hATTR) with polyneuropathy (formerly known as Familial Amyloid Polyneuropathy) is a rare disease due to mutations in the gene encoding transthyretin (TTR) and characterized by multisystem extracellular deposition of amyloid, leading to dysfunction of different organs and tissues. hATTR amyloidosis represents a diagnostic challenge for neurologists considering the great variability in clinical presentation and multiorgan involvement. Generally, patients present with polyneuropathy, but clinicians should consider the frequent cardiac, ocular and renal impairment. Especially a hypertrophic cardiomyopathy, even if usually latent, is identifiable in at least 50% of the patients. Therapeutically, current available options act at different stages of TTR production, including synthesis inhibition (liver transplantation and/or gene-silencing drugs) or tetramer TTR stabilization (TTR stabilizers), increasing survival at different disease stages.

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Hereditary transthyretin amyloidosis: a model of medical progress for a fatal disease

Hereditary amyloidogenic transthyretin (ATTRv) amyloidosis with polyneuropathy (also known as familial amyloid polyneuropathy) is a condition with adult onset caused by mutation of transthyretin (TTR) and characterized by extracellular deposition of amyloid and destruction of the somatic and autonomic PNS, leading to loss of autonomy and death. This disease represents a model of the scientific and medical progress of the past 30 years. ATTRv amyloidosis is a worldwide disease with broad genetic and phenotypic heterogeneity that presents a diagnostic challenge for neurologists. The pathophysiology of the neuropathy is increasingly understood and includes instability and proteolysis of mutant TTR leading to deposition of amyloid with variable lengths of fibrils, microangiopathy and involvement of Schwann cells. Wild-type TTR is amyloidogenic in older individuals. The main symptoms are neuropathic, but the disease is systemic; neurologists should be aware of cardiac, eye and kidney involvement that justify a multidisciplinary approach to management. Infiltrative cardiomyopathy is usually latent but present in half of patients. Disease-modifying therapeutics that have been developed include liver transplantation and TTR stabilizers, both of which can slow progression of the disease and increase survival in the early stages. Most recently, gene-silencing drugs have been used to control disease in the more advanced stages and produce some degree of improvement.

Congo Red and amyloids: history and relationship

Staining with Congo Red (CR) is a qualitative method used for the identification of amyloids in vitro and in tissue sections. However, the drawbacks and artefacts obtained when using this dye can be found both in vitro and in vivo. Analysis of scientific data from previous studies shows that CR staining alone is not sufficient for confirmation of the amyloid nature of protein aggregates in vitro or for diagnosis of amyloidosis in tissue sections. In the present paper, we describe the characteristics and limitations of other methods used for amyloid studies. Our historical review on the use of CR staining for amyloid studies may provide insight into the pitfalls and caveats related to this technique for researchers considering using this dye.

Amyloidosis: Insights from Proteomics

Amyloidoses are a spectrum of disorders caused by abnormal folding and extracellular deposition of proteins. The deposits lead to tissue damage and organ dysfunction, particularly in the heart, kidneys, and nerves. There are at least 30 different proteins that can cause amyloidosis. The clinical management depends entirely on the type of protein deposited, and thus on the underlying pathogenesis, and often requires high-risk therapeutic intervention. Application of mass spectrometry-based proteomic technologies for analysis of amyloid plaques has transformed the way amyloidosis is diagnosed and classified. Proteomic assays have been extensively used for clinical management of patients with amyloidosis, providing unprecedented diagnostic and biological information. They have shed light on the pathogenesis of different amyloid types and have led to identification of numerous new amyloid types, including ALECT2 amyloidosis, which is now recognized as one of the most common causes of systemic amyloidosis in North America.

Decreasing incidence of AA amyloidosis in Spain

BACKGROUND

The main objectives of our study were to review all cases of amyloidosis diagnosed by renal biopsy in Spain from 1994 to 2009 and to analyse variations in the incidence over time.

MATERIALS AND METHODS

We analysed all biopsies from native kidneys included in the Spanish Registry of Glomerulonephritis. A total of 120 centres provided 17 680 biopsies over 16 years. Follow-up was divided in four periods.

RESULTS

We collected 653 cases of renal amyloidosis. In 438 cases (67%), amyloidosis type was specified, [AA amyloidosis, 253 cases (57·8%); AL amyloidosis, 185 cases (42·2%)]. Mean age was 60 (17·8) years; 51·4% of patients were younger than 65. Overall incidence was 3·7%. In patients < 65, AA amyloidosis was present in 66·1% and AL amyloidosis in 33·9% (P < 0·01). No differences were found in patients > 65. Patients with AA amyloidosis were younger (56·8 vs. 64·0, P < 0·01) and had worse creatinine clearance (35 vs. 57 mL/min, P < 0·01). We found a decrease in the incidence among biopsies collected during each of the 4 study periods (4·2%, 3·9%, 3·5% and 3·2%, respectively, P < 0·001).

CONCLUSIONS

This is the largest series of renal amyloidosis in kidney biopsies published to date. We found amyloidosis to be decreasing slowly in Spain. This decrease affects both types and is confirmed in all cases marked in patients < 65 and in AA type. AA amyloidosis was the most frequent in our series. Patients affected by it were younger and had worse kidney function, with no differences in the level of proteinuria.

Detection of amyloid in abdominal fat pad aspirates in early amyloidosis: Role of electron microscopy and Congo red stained cell block sections

Background:

Fine-needle aspiration biopsy (FNA) of the abdominal fat pad is a minimally invasive procedure to demonstrate tissue deposits of amyloid. However, protocols to evaluate amyloid in fat pad aspirates are not standardized, especially for detecting scant amyloid in early disease.

Materials and Methods:

We studied abdominal fat pad aspirates from 33 randomly selected patients in whom subsequent tissue biopsy, autopsy, and/or medical history for confirmation of amyloidosis (AL) were also available. All these cases were suspected to have early AL, but had negative results on abdominal fat pad aspirates evaluated by polarizing microscopy of Congo Red stained sections (CRPM). The results with CRPM between four reviewers were compared in 12 cases for studying inter observer reproducibility. 24 cases were also evaluated by ultrastructural study with electron microscopy (EM).

Results:

Nine of thirty-three (27%) cases reported negative by polarizing microscopy had amyloidosis. Reanalysis of 12 mixed positive-negative cases, showed considerable inter-observer variability with frequent lack of agreement between four observers by CRPM alone (Cohen's Kappa index of 0.1, 95% CI -0.1 to 0.36). EM showed amyloid in the walls of small blood vessels in fibroadipose tissue in four out of nine cases (44%) with amyloidosis.

Conclusion:

In addition to poor inter-observer reproducibility, CRPM alone in cases with scant amyloid led to frequent false negative results (9 out of 9, 100%). For improved detection of AL, routine ultrastructural evaluation with EM of fat pad aspirates by evaluating at least 15 small blood vessels in the aspirated fibroadipose tissue is recommended. Given the high false negative rate for CRPM alone in early disease, routine reflex evaluation with EM is highly recommended to avert the invasive option of biopsying various organs in cases with high clinical suspicion for AL.

Performing and processing FNA of anterior fat pad for amyloid

Historically, heart, liver, and kidney biopsies were performed to demonstrate amyloid deposits in amyloidosis. Since the clinical presentation of this disease is so variable and non-specific, the associated risks of these biopsies are too great for the diagnostic yield. Other sites that have a lower biopsy risk, such as skin or gingival, are also relatively invasive and expensive. In addition, these biopsies may not always have sufficient amyloid deposits to establish a diagnosis. Fat pad aspiration has demonstrated good clinical correlation with low cost and minimal morbidity. However, there are no standardized protocols for performing this procedure or processing the aspirated specimen, which leads to variable and nonreproducible results. The most frequently utilized modality for detecting amyloid in tissue is an apple-green birefringence on Congo red stained sections using a polarizing microscope. This technique requires cell block preparation of aspirated material. Unfortunately, patients presenting in early stage of amyloidosis have minimal amounts of amyloid which greatly reduces the sensitivity of Congo red stained cell block sections of fat pad aspirates. Therefore, ultrastructural evaluation of fat pad aspirates by electron microscopy should be utilized, given its increased sensitivity for amyloid detection. This article demonstrates a simple and reproducible procedure for performing anterior fat pad aspiration for the detection of amyloid utilizing both Congo red staining of cell block sections and electron microscopy for ultrastructural identification.

[Systemic amyloidosis: practical diagnosis]

Amyloid deposits have particular ultrastructural appearance with 7 to 10 nm-diameter fibrils. Amyloid is defined by its tinctorial affinity, which includes Congo red positivity, which must polarize and produce apple-green birefringence. Immunohistochemical characterization allows to know the origin of amyloidosis (characterization, which must be performed on frozen tissue). This restatement is proposed to renal pathologists in indicating the traps of studying amyloidosis, the tissues performing for the diagnosis, the specific staining and the immunohistochemical characterization.

Diagnosis and typing of systemic amyloidosis: The role of abdominal fat pad fine needle aspiration biopsy

Introduction:

Systemic amyloidosis (SA) has a broad nonspecific clinical presentation. Its diagnosis depends on identifying amyloid in tissues. Abdominal fat pad fine needle aspiration (FPFNA) has been suggested as a sensitive and specific test for diagnosing SA.

Materials and Methods:

Thirty-nine FPFNA from 38 patients (16 women and 20 men, age range 40–88 years) during a 15-year period were reviewed. Smears and cell blocks were stained with Congo red (CR). A panel of antibodies (serum amyloid protein, serum amyloid A, albumin, transthyretin, kappa light chain and lambda light chain) was used on six cell blocks from five patients. The FNA findings were correlated with clinical and histological follow-up.

Results:

FPFNAs were positive, confirmed by CR in 5/39 (13%), suspicious in 1/39 (3%), negative in 28/39 (72%), and insufficient for diagnosis in 5/39 (13%) of cases. In all the positive cases, SA was confirmed within 2–16 weeks. Among the 28 negative cases, SA was diagnosed in 21, the rest were lost to follow-up. Among the insufficient cases, SA was diagnosed in four and one was lost to follow-up. Specificity was 100%, whereas sensitivity was 19%. SA typing using cell block sections was successful in three, un-interpretable in one, and negative in two cases.

Conclusion:

FPFNA for SA is not as good as previously reported. This may be due to different practice setting, level of experience, diagnostic technique, or absence of abdominal soft tissue involvement. A negative result of FPFNA does not exclude SA. Immune phenotyping of amyloid is possible on cell block.

[Amyloid centers in Europe: the EURAMY project]

The systemic amyloidoses comprise a large group of serious protein deposition diseases. Although rather rare, the disorders are spread all over the world. Increasing understanding of pathogenic mechanisms and recent hope for treatment options demand further research and development of diagnostic procedures. The European Union Framework 6 program EURAMY (http://www.EURAMY.org) is devoted to all aspects of research on systemic amyloidoses, from molecular aspects to treatment of patients.

Generation of Amyloid A Protein by the Cell Lines from Amyloid-Susceptible and -Resistant Mice

It has been proposed that impaired degradation is the cause of amyloid A (AA) formation in reactive amyloidosis (Ham et al., Scand J Immunol 1997; 45: 354-60). The current SDS-PAGE of the culture medium showed that the macrophage cell line from the amyloid-susceptible mouse strain (ANA1) degraded amyloid precursor protein serum amyloid A into the AA-like amyloidogenic product of approximately 8.6 kDa but went no further, whereas cells from the resistant strain (A/J10) cleared the AA-like derivates proceeding to approximately 7.7 kDa products within the incubation period. Degradation occurred in the chemically defined medium at a slower rate than in the medium with serum. This may imply that a lack of the serum components as well as impaired degradation could contribute to the development of amyloidosis.

Primary systemic amyloidosis

Primary amyloidosis is a plasma cell dyscrasia in which insoluble immunoglobulin light chain fragments are produced and polymerize into fibrils that deposit extracellularly, causing visceral organ dysfunction and death. The disorder is rare. Its recognition requires understanding the association between nephrotic syndrome, cardiomyopathy, peripheral neuropathy, and hepatomegaly with amyloidosis. The most important screening test for amyloidosis is immunofixation of the serum and urine to detect a monoclonal immunoglobulin light chain. All patients need the diagnosis confirmed histologically. The least invasive source of tissue for amyloid detection is the subcutaneous fat. The most important prognostic factor is whether there is cardiac involvement, which is best assessed by echocardiography with Doppler studies. Therapies used include oral melphalan/prednisone and high-dose corticosteroids. High-dose chemotherapy followed by stem cell reconstitution seems to provide the highest reported response rates. Transplant is associated with unique morbidities not seen in the transplantation of patients with other hematologic malignancies.

Value of testis biopsy in the diagnosis of systemic amyloidosis

OBJECTIVES

To evaluate testis biopsy as a diagnostic tool in systemic amyloidosis, to assess how amyloidosis affects testicular tissue, and to examine the relationship between testicular amyloidosis and infertility.

METHODS

Testicular biopsies from 72 patients with confirmed systemic amyloidosis were examined for amyloid deposition after Congo red and crystal violet staining. A rectal biopsy was also done in each case, and the results were compared with the testicular biopsy findings.

RESULTS

Testicular amyloid deposition was detected in 62 (86.1%) of 72 patients. Fifty-one (85%) of 60 patients with secondary amyloidosis, 11 (91.7%) of 12 patients with primary amyloidosis, and 28 (87.5%) of 32 patients with familial Mediterranean fever showed amyloid deposition in the testis. Rectal biopsies were positive in 40 cases (55.6%). Only 4 of the 62 patients with testicular amyloid showed normal spermatogenesis. The remaining 58 exhibited abnormal spermatogenesis, and 77.7% of patients had seconder infertility. Of 62 patients with positive testis biopsies, 30 had serum creatinine levels less than 1.5 mg/dL, and 29 patients with testicular amyloid manifested nephrotic syndrome.

CONCLUSIONS

The testis biopsy is a valuable and more sensitive method than rectal biopsy for diagnosing systemic amyloidosis. The results also showed that testicular amyloidosis causes infertility at a higher rate than expected.

Immunoglobulin light chain amyloidosis and the kidney

Immunoglobulin light chain amyloidosis and the kidney. Amyloidosis (AL) is a common cause of nephrotic syndrome in nondiabetic, nonhypertensive adults. All adult patients with nephrotic syndrome should have immunofixation of serum and urine as a screen. The finding of a monoclonal protein, particularly of lambda type, should lead to a subcutaneous fat aspirate or bone marrow biopsy to search for amyloid deposits. When the result of either test is positive, a kidney biopsy is unnecessary. The prognosis of patients who have renal amyloidosis depends on the concentration of serum creatinine at presentation and whether an echocardiographic evaluation demonstrates infiltrative cardiomyopathy. Most therapies are directed against the plasma cell dyscrasia present in all patients with AL and can include melphalan and prednisone, high-dose dexamethasone, and, most recently, peripheral blood stem cell transplantation.

Protein misfolding and disease; protein refolding and therapy

Diverse human disorders, including several neurodegenerative diseases and systemic amyloidosis, are thought to arise from the misfolding and aggregation of an underlying protein. Recent findings strongly support this hypothesis and have increased our understanding of the molecular mechanism of protein conformational disorders. Many questions are still pending, but the data overall suggest that correction of protein misfolding constitutes a viable therapeutic strategy for conformational diseases.

Amyloidosis

Amyloidosis is considered rare but has an incidence similar to that of Hodgkin's disease and chronic granulocytic leukemia. The diagnosis should be considered in any patient with unexplained nephrotic-range proteinuria, heart failure, peripheral neuropathy, or hepatomegaly. If a monoclonal protein is found in a patient with any of these clinical presentations, a biopsy should be performed and the specimen stained with Congo red. The simplest source of diagnostic material is subcutaneous fat tissue. Treatment usually consists of chemotherapy, which may be oral and low dose or high dose with stem cell rescue.

[Value of the biopsy of accessory salivary glands in amyloidosis]

PURPOSE

To assess the value of accessory salivary gland biopsy for the diagnosis of amyloidosis, a study was conducted in the nephrology and hemodialysis department at Ibn Rochd University Hospital from February 1996 to January 1998.

METHODS

Renal amyloidosis was confirmed by renal biopsy accompanying accessory salivary gland biopsy.

RESULT

The patient's mean age was 39 years old (range 15-80), with a 4:1-male/female ratio. An infectious cause (either tuberculosis or superinfection and dilatation of the bronchi) was the most frequent (70% of the cases) etiology. All the patients presented renal symptomatology. Nephrotic syndrome predominated. Amyloid deposits were observed in 100% of renal needle biopsies and in 80% of accessory salivary gland biopsies.

CONCLUSION

Renal biopsy led to more positive cases than the other biopsies. It may be accompanied by severe complications. Furthermore, biopsy of the accessory salivary glands is a simple and very reliable technique for the diagnosis of amyloidosis. It is currently the best diagnostic test.

A quantitative method for detecting deposits of amyloid A protein in aspirated fat tissue of patients with arthritis

OBJECTIVE

To describe a new, quantitative, and reproducible method for detecting deposits of amyloid A protein in aspirated fat tissue and to compare it with smears stained with Congo red.

METHODS

After extraction of at least 30 mg of abdominal fat tissue in guanidine, the amyloid A protein concentration was measured by a monoclonal antibody-based sandwich ELISA.

RESULTS

The concentrations in 24 patients with arthritis and AA amyloidosis (median 236, range 1.1-8530 ng/mg tissue) were higher (p < 0.001) than in non-arthritic controls, uncomplicated rheumatoid arthritis, and other types of systemic amyloidosis (median 1.1, range 1.1-11.6 ng/mg tissue). Patients with extensive deposits, according to Congo red staining, had higher concentrations than patients with minute deposits.

CONCLUSION

This is a new, quantitative, and reproducible method for detecting deposits of amyloid A protein in aspirated fat tissue of patients with arthritis, even when minute deposits are present as detected in smears stained with Congo red.

Extended analysis of AL-amyloid protein from abdominal wall subcutaneous fat biopsy: kappa IV immunoglobulin light chain

In AL-amyloidosis the cause of amyloid fibril formation in beta-pleated sheets from the precursor protein immunoglobulin light chain is not established, but studies of AL-proteins indicate that amino acid substitutions are important in the pathogenesis. Amyloid material was extracted from a subcutaneous fat tissue biopsy and submitted to extended protein separation, typing and amino acid sequence analyses. The AL-protein belonged to the rare immunoglobulin light chain kappa, subtype kappa IV and contained unique amino acid substitutions, mostly in the highly preserved framework regions. The study shows that subcutaneous fat biopsies are useful sources of amyloid material for biochemical studies.