#5339 TRANSTHYRETIN AMYLOIDOSIS WITH BIOPSY PROVEN RENAL INVOLVEMENT

Abstract

Abstract Background and Aims Systemic amyloidosis is a cluster of disorders characterized by tissue deposition of amyloid (highly ordered fibrils composed of low molecular weight subunits of a variety of proteins). Transthyretin (TTR) amyloidosis (ATTR) is either an autosomal dominant inherited condition (ATTRv, where v stands for “variant”) or a non hereditary disease due to misfolding of wild-type TTR (ATTRwt). ATTR is likely underdiagnosed due to its clinical variability and lack of specific symptoms or biomarkers. The first aim of the study is to emphasise the importance of suspecting ATTR when facing certain clinical manifestations in association with renal impairment and urinary abnormalities. Furthermore, renal biopsy provides crucial information for a correct diagnosis and treatment approach. Method We report 5 cases of biopsy-proven renal ATTR deposition in patients presenting with mild to moderate renal impairment and mild urinary abnormalities. The TTR precursor has been confirmed in kidney specimens by immunohistochemistry. Genotyping was carried out in every patient. Results The presence of amyloid was found in all patients, with different distribution (#1-3 pericapsular and vascular; #2 vascular; #4 mesangial, vascular, in tubular basement membrane and in the interstitium of cortex and medulla; #5 pericapsular, vascular and interstitial). On genetic analysis three patients were wild-type (#1-2-5), one carried the c.424G>A (p.(Val142Ile)) mutation (#3) and the last one the Val30Met mutation (#4). Conclusion Suspicion of ATTR should be considered in patients with increase in serum creatinine, mild proteinuria and cardiac and peripheral nerve symptoms. This can be of utmost importance in elderly patients in whom a monoclonal gammopathy of undetermined significance can co-exist and drive a wrong diagnosis of primary light chain amyloidosis (AL), that could lead the clinician to undertake inappropriate treatments. Renal biopsy and genetic sequencing are both critical in diagnosing ATTR. Finally, we suggest distinguishing in the context of the ATTR deposition disease an ATTR nephropathy characterized by mesangial accumulation of amyloid, that impacts functional and urinary assessment, from isolated deposition in small vessels without specific clinical consequences, albeit critical for ATTR diagnosis.