600104 Disclosed is a one-vector expression system comprising: a first and a second expression cassette, wherein said first expression cassette comprises a nucleotide sequence comprising a first promoter sequence operably linked to a first nucleotide sequence, said first nucleotide sequence encoding a GTP cyclohydrolase 1 (GCH1； EC 3.5.4.16) polypeptide or a biologically active fragment or variant thereof, and wherein said second expression cassette comprises a nucleotide sequence comprising a second promoter sequence operably linked to a second nucleotide sequence said second nucleotide sequence encoding a tyrosine hydroxylase (TH； EC 1.14.16.2) polypeptide or a biologically active fragment or variant thereof, and wherein the vector is an adeno associated vector (AAV) and wherein said second nucleotide sequence is operably linked to a Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE), and wherein both said first and said second promoter are Synapsin1 promoters.
