396 ARE BLOOD LEVELS OF RETINOL BINDING PROTEIN USEFUL IN DIAGNOSING ATTR-CA? A NEGATIVE STUDY, SO FAR


 
 
 Retinol binding protein (RBP) is a protein synthesized in the liver which forms, along with transthyretin (TTR) the retinol-transport-complex. This complex ligates retinol and thyroxine and transports them in the human plasma. TTR is a protein longer and heavier than RBP. It ligates RBP preventing its renal filtration. Our hypothesis is that the relationship between RBP and TTR is dual: TTR avoids renal filtration of RBP, but also RBP itself, functioning as an endogenous ligand, has an action on TTR by stabilizing and avoiding TTR misfolding.
 Misfolded TTR proteins form amyloid fibrils rich in beta-cross-sheets that can infiltrate healthy tissues altering their physiology. The infiltration of these fibrils in the cardiac tissue leads to the well-known condition of TTR cardiac amyloidosis (ATTR CA).
 Our hypothesis is that the lack of TTR stabilization that can happen with low blood levels of RBP is a risk factor for developing ATTR CA. The main goal of our study is to understand if high or normal values of RBP can help exclude any pathological condition linked to the accumulation of misfolded TTR proteins.
 
 
 
 All patients referred to our Cardiomyopathy Clinic with a clinical and echographic suspicion of CA were consecutively enrolled. All patients underwent a complete diagnostic workup in order to confirm or exclude CA, comprehending lab tests (including RBP4), SPECT, cardiac MR, genetic testing and cardiac biopsy as recommended by current recommendations. At the end of the diagnostic process, patients with ATTR-wt CA were enrolled as cases, and patients with no CA were considered as controls. Patients with ATTR-mutated CA or AL CA were excluded from the present analysis.
 
 
 
 Fifty-nine consecutive patients (42 males, age 77+/-13 years) were enrolled. Of those, 27 had a definitive diagnosis of ATTR-wt CA, while 32 had another diagnosis. Mean levels of RBP4 were not different between patients with and without CA (5.4+/-1.9 vs. 5.0+/-1.8 mg/dl; p=ns) as were Troponin I, BNP and NT-proBNP levels (all p=ns). Among patients with a definitive diagnosis of ATTR-wt CA and a positive SPECT, RBP4 levels were similar between Perugini 2 and 3 scores (5.4+/-2.1 vs. 5.6+/-2.0 mg/dl; p=ns).
 
 
 
 From our findings, it seems that there is no significant correlation between low levels of RBP and the presence of ATTR CA as we found no difference in the distribution of RBP levels between cases and controls. It also did not seem to be a useful marker to stratify the levels of myocardial infiltration as long as there is no difference in RBP between Perugini score 2 and 3.
