Parkinson’s disease (PD) without (non-demented,PDND) and with dementia (PDD),and dementia with Lewy bodies (DLB) are subsumed under the umbrella term Lewy body disorders (LBD).The main component of the underlying pathologic substrate,i.e.Lewy bodies and Lewy neurites,is misfolded -synuclein (Asyn),and – in particular in demented LBD patients – cooccurring misfolded Amyloid beta (Abeta).Transthyretin (TTR),a clearance protein produced in the periphery and,autonomously,in the central nervous system,is associated with Abeta accumulation in Alzheimer’s disease.In addition,a recent study suggests that TTR is involved in Asyn clearance.We measured TTR protein levels in serum and cerebrospinal fluid (CSF) of 131 LBD patients (77 PDND,26 PDD,and 28 DLB) and 72 controls,and compared TTR levels with demographic and clinical data as well as neurodegenerative markers of the CSF.Five single nucleotide polymorphisms of the TTR gene which are considered to influence the ability of the protein to carry its ligands were also analyzed.CSF TTR levels were significantly higher in LBD patients compared to controls.Post-hoc analyses demonstrated that this effect was driven by PDND patients.In addition,CSF TTR levels correlated negatively with CSF Abeta1-42,total tau and p-tau levels.In serum,demented LBD patients showed significantly lower levels than controls.There was no relevant association between TTR levels and genetic,demographic and clinical data,respectively.These results suggest an involvement of the clearance protein TTR in LBD pathophysiology.