The Motor Phenotype of Parkinson's Disease in Relation to Age at Onset by Wickremaratchi, M, Knipe, M, Sastry, B, Morgan, E, Jones, A, Salmon, R, Weiser, R, Moran, M, Davies, D, Ebenezer, L, Raha, S, Robertson, N, Butler, C, Ben-Shlomo, Y, Morris, H