Increased alpha-synuclein levels are pathogenic in Parkinson disease as evidenced by gene copy number mutations and increased alpha-synuclein levels detected in some familial and sporadic Parkinson disease cases respectively. Increased gene expression levels can result in a number of ways, such as changes in the transcriptional and post-transcriptional control of gene expression. The 3'UTR of mRNAs are powerful mediators of post-transcriptional control. To determine the role of the 3'UTR of human alpha-synuclein in gene expression regulation, we first examined its degree of sequence conservation and demonstrated very high conservation throughout the 3'UTR of human alpha-synuclein. Using EST and RT-PCR analyses, we determined the sequence of all 3'UTRs of human alpha-synuclein generated by alternative polyadenylation. Using luciferase reporter assays, we demonstrated that alternative polyadenylation in this gene generates functionally distinct 3'UTR species, and that the first 574 nt of the 3'UTR of human alpha-synuclein is a composite sequence, consisting of a proximal domain that suppresses gene expression and a distal domain that stimulates it. In confirmation of the luciferase assay data, the RNA binding protein hnRNP C1/C2 was shown to bind to the proximal domain of the 3'UTR of alpha-synuclein and suppress gene expression. The identification of a single nucleotide polymorphism, which is located at the distal end of the 3'UTR of human alpha-synuclein and increases gene expression by 32%, confirmed that this 3'UTR segment stimulates gene expression. Altogether, our data have identified a clinically significant polymorphism for Parkinson disease and demonstrated that the 3'UTR of human alpha-synuclein contains at least 2 domains that can control gene expression.