Because serum BDNF was lower in PD patients with RLS than without RLS (p < 0.001, Figure 1A), the serum BDNF cutoff value of 3,638 pg/ml had a 78% sensitivity and an 81% specificity for distinguishing between PD patients with RLS and without RLS, with an area under the curve of 0.82 (Figure 1B). This evidence concerns the gene BDNF and Parkinson disease.