Renal amyloidosis caused by apolipoprotein A-II without a genetic mutation in the coding sequence

Although the majority of renal amyloidosis is caused by either acquired monoclonal immunoglobulin light-chain amyloidosis or reactive systemic amyloid A, some cases are caused by hereditary amyloidosis. Apolipoprotein A-II (apoAII) amyloidosis is a rare form of hereditary amyloidosis and cannot be diagnosed by a routine examination. Thus, the prevalence and etiology of apoAII amyloidosis are uncertain. In humans, a genetic mutation in the stop codon of apoAII is considered to be a cause of amyloid fibril formation. We report on a 68-year-old man who presented with proteinuria by apoAII amyloidosis without family history. His proteinuria gradually increased to 6 g/day within 1 year. A renal biopsy showed amyloid deposition in the glomeruli, however, acquired monoclonal immunoglobulin light-chain amyloidosis and reactive systemic amyloid A were ruled out. Immunohistochemistry revealed apoAII deposition in the glomeruli, but DNA sequencing did not identify any genetic mutation in the coding sequence of apoAII. Here, we report a case of apoAII amyloidosis without a genetic mutation in the coding sequence and discuss the etiology of apoAII amyloidosis.