Parkinson disease (PD) is the most important movement disorder and about 50% of 
patients develop dementia over the time. PD belongs to the group of Lewy body 
disorders. Alpha-synuclein (AS) is the main component of Lewy bodies and its 
aggregation is a key event in the pathogenesis of PD. Beta-synuclein (BS) 
inhibits AS aggregation in vitro and in vivo and has been shown to interact 
directly with AS regulating its functionality and preventing its 
oligomerization. Recently, we have described a molecular subgroup of DLB 
characterized by the drastic BS reduction in cortical areas. In this study we 
have analyzed the expression of two BS transcripts and the main AS transcript 
SNCA140, in frozen samples of three brain areas, temporal cortex, caudate 
nucleus and pons, from patients with PD and PDD in comparison with controls. 
Relative mRNA expression was determined by real-time PCR with SybrGreen, 
neuron-specific-enolase as housekeeping gene and the deltadeltaCt method. The 
most important difference in BS and AS mRNA expression between PD and PDD was 
found in the caudate nucleus, where BS mRNA was overexpressed in PD and AS mRNA 
diminished in PDD. Our findings provide new insights into the pathogenesis of 
dementia in PD, indicating that differential BS and AS expression in the caudate 
nucleus may represent one of the molecular mechanisms involved in these complex 
diseases.