Complement neoantigen and vitronectin are components of plaques in amyloid AL neuropathy

Epidemiology of ATTRV30M neuropathy in Cyprus and the modifier effect of complement C1q on the age of disease onset

BACKGROUND

ATTRV30M amyloidosis is a lethal autosomal dominant sensorimotor and autonomic neuropathy caused by amyloid deposition composed of aggregated misfolded TTR monomers with the V30M mutation. The age of onset in patients with ATTRV30M varies in different foci and the mechanism behind it is still unknown.

METHODS

The tertiary neurology center following all ATTRV30M patients in Cyprus was used to collect demographic data to estimate; prevalence, incidence, penetrance, anticipation, time from disease onset to diagnosis and transplantation. Ocular, cardiac and leptomeningeal involvement in transplanted patients was explored. Correlation of C1q tagging SNPs with age of disease onset was carried out.

RESULTS

Prevalence and incidence for ATTRV30M neuropathy in Cyprus are 5.4/100,000 and 0.3/100,000 respectively. Mean age of onset is 40.6 years and anticipation is 8.3 years. Penetrance reaches 51% and 75% by the ages of 50 and 80 years respectively. In liver transplanted patients rates of ocular, cardiac and leptomeningeal involvement were estimated to be 60%, 20% and 16%, respectively. C1q polymorphisms correlated with age of disease onset.

CONCLUSIONS

ATTRV30M neuropathy has a rising prevalence in Cyprus due to improved survival of patients. Late onset complications are becoming a major problem. Complement C1q appears to be a modifier in this disease.

A case of isolated amyloid light-chain amyloidosis of the radial nerve

Peripheral nerve involvement may be the first sign of systemic amyloid light-chain (AL) amyloidosis, a rare disease. Physical examination and electrodiagnostic testing are the mainstays of peripheral neuropathy evaluation at presentation. Sural nerve biopsy is performed in conjunction with serum and urine protein evaluation to differentiate between focal and systemic disease. Systemic disease is treated with a combination of chemotherapy, steroids, and stem cell transplantation. Isolated peripheral nerve disease is extremely rare. The authors here report the case of an 80-year-old woman who presented with progressive right upper-extremity weakness due to right radial neuropathy discovered upon electrodiagnostic testing. Magnetic resonance neurography (MRN) revealed a focal lesion within the right radial nerve. She underwent radial nerve exploration and excision of an intraneural mass consisting of amyloid on histopathology, with mass spectrometry analysis diagnostic for AL amyloidosis. Noninvasive testing and clinical history did not suggest systemic involvement. This unique case of isolated peripheral nerve AL amyloidosis in the absence of signs and symptoms of systemic disease is described, and the literature demonstrating peripheral nerve involvement in AL amyloidosis is reviewed.

MALDI-mass spectrometry imaging identifies vitronectin as a common constituent of amyloid deposits

Amyloids are pathological intra- and extracellular fibrillar aggregates of polypeptides with a cross-β-sheet structure and characteristic tinctorial properties. The amyloid deposits commonly enclose several non-fibrillar components of the extracellular matrix. Their potential to regulate the formation and aggregation process of amyloid fibrils is still poorly understood. For a better understanding of the role of the extracellular matrix in amyloidosis, it is essential to gain deeper insights into the composition of amyloid deposits. Here, we utilized matrix-assisted laser desorption and ionization mass spectrometry imaging to identify extracellular matrix compounds in amyloid deposits. Using this technique, we identified and determined the spatial distribution of vitronectin within AApoAI-, ALλ-, ATTR- and AIns amyloid deposits and, using immunohistochemistry, validated the spatial overlap of vitronectin with amyloids in 175 cases with diverse types of amyloid in several different tissues.

Complement activation in acquired and hereditary amyloid neuropathy

The pathogenesis of the axonal degeneration in acquired or hereditary amyloidosis is unknown. In this immunohistochemistry study, we examined 20 sural nerve biopsies from individuals with amyloid neuropathy (14 acquired and 6 hereditary) for evidence of complement activation. Complement activation products were detected on and around amyloid deposits within peripheral nerves. We found no difference in the extent, location or pattern of complement activation products between the 2 forms of amyloidosis. The presence of early classical pathway activation markers in the absence of antibody in hereditary cases suggests an antibody-independent activation of the classical pathway through binding of C1q. The lack of Factor Bb-suggested alternative pathway activation was not significant in these cases. The detection of C5b-9 neoantigen on amyloid deposits demonstrated that the full complement cascade was activated. Complement activation on amyloid deposits and the generation of C5b-9 in vivo may contribute to bystander injury of axons in the vicinity of amyloid deposits.