👤 Karen L Grogg

Apolipoprotein A-IV associated amyloidosis (AApoAIV amyloidosis) is a rare cause of amyloidosis with only a single reported case. Here we describe the clinical, biopsy, and mass spectrometry characteristics of 11 cases of renal AApoAIV amyloidosis encompassing 9 men and 2 women with a mean age at diagnosis of 63.5 years. Progressive chronic kidney disease (mean serum creatinine 2.9 mg/dl) was the most common cause for biopsy with proteinuria absent or minimal in all except one. Hematological and serological evaluation was negative in 9 patients, while 2 had a monoclonal gammopathy. The renal biopsy findings were striking and showed large amounts of eosinophilic Congo-red positive amyloid deposits restricted to the renal medulla with sparing of the renal cortex. In 6 cases, peritubular amyloid was noted in addition to the interstitial involvement. Immunofluorescence studies were negative for immunoglobulins. Electron microscopy showed nonbranching fibrils measuring 7 to 10 nm in diameter. Laser microdissection of the amyloid deposits followed by mass spectrometry showed large spectra number (a semiquantitative measure of abundance) for AApoAIV protein ranging from 49 to 169 (average 85), serum amyloid protein (average 19), and apolipoprotein E (average 48). Importantly, no peptides were detected for any other forms of known amyloidogenic precursor proteins. Thus, renal AApoAIV amyloidosis typically presents with progressive chronic kidney disease and histologically exhibits extensive medullary involvement with sparing of the cortex. The diagnosis is best established by mass spectrometry. Hence, a high degree of suspicion and examination of the renal medulla is required to make the diagnosis. Show less

Examination of abdominal subcutaneous fat aspirates is a practical, sensitive and specific method for the diagnosis of systemic amyloidosis. Here we describe the development and implementation of a clinical assay using mass spectrometry-based proteomics to type amyloidosis in subcutaneous fat aspirates. First, we validated the assay comparing amyloid-positive (n=43) and -negative (n=26) subcutaneous fat aspirates. The assay classified amyloidosis with 88% sensitivity and 96% specificity. We then implemented the assay as a clinical test, and analyzed 366 amyloid-positive subcutaneous fat aspirates in a 4-year period as part of routine clinical care. The assay had a sensitivity of 90%, and diverse amyloid types, including immunoglobulin light chain (74%), transthyretin (13%), serum amyloid A (%1), gelsolin (1%), and lysozyme (1%), were identified. Using bioinformatics, we identified a universal amyloid proteome signature, which has high sensitivity and specificity for amyloidosis similar to that of Congo red staining. We curated proteome databases which included variant proteins associated with systemic amyloidosis, and identified clonotypic immunoglobulin variable gene usage in immunoglobulin light chain amyloidosis, and the variant peptides in hereditary transthyretin amyloidosis. In conclusion, mass spectrometry-based proteomic analysis of subcutaneous fat aspirates offers a powerful tool for the diagnosis and typing of systemic amyloidosis. The assay reveals the underlying pathogenesis by identifying variable gene usage in immunoglobulin light chains and the variant peptides in hereditary amyloidosis. Show less