MAPT and Parkinson disease: While certain gene mutations (e.g. PARKIN mutations) are associated with a more favourable disease course in PD, other gene mutations including glucocerebrosidase (GBA) mutations52–54 and the presence of the MAPT H1/H1 genotype have been found to be associated a more rapid course of cognitive decline in PD patients and a higher risk of developing PDD.55,56 As genetic testing was not undertaken in this study, it is impossible to know the possible impact of such effects.