GRN and Parkinsonism: For instance, the MAPT pathway is involved in the aetiopathogenesis of Alzheimer’s disease (AD), Parkinson’s disease (PD), parkinsonism, and amyotrophic lateral sclerosis (ALS) [14,15,16]; GRN in AD, PD, parkinsonism, motor neuron disease (MND) [17,18,19,20]; and C9orf72 in ALS, AD, and parkinsonism [21].