SNCA and Parkinson disease: Additionally, the alpha-synuclein gene (SNCA) Rep1 promoter region, a polymorphic microsatellite repeat upstream of the SNCA transcription start site that enhances SNCA transcription and α-synuclein expression [5], has been shown in multiple cohorts to be a risk factor for sporadic PD in carriers of long Rep1 alleles [6, 7].