Quantitative evaluations of TH-immunoreactive fibres revealed densities ∼2–3 times greater with combined nigral and putamenal CERE120 delivery than putamen alone (Fig. 4L), which in turn was 1.3–1.8 times higher than in the Parkinson’s disease patients who did not undergo gene therapy (Fig. 4L). The gene discussed is TH; the disease is Parkinson disease.