SNCA and Parkinson disease: In the MAD study, following the third intravenous infusion of MEDI1341 (Day 57) in participants with Parkinson’s disease, mean (SD) change from baseline in plasma total α-synuclein increased and peaked at Days 61 (506% [374]) and 71 (648% [346]) for the 1200 and 2000 mg doses, respectively, before decreasing towards baseline levels (Fig. 4A).