A recent meta-analysis from our group confirmed cholinesterase inhibitors to be effective for treatment of hallucinations and delusions in PD, albeit with small effect sizes.47 These small effect sizes might be explained, in part, by the multifactorial aetiology of VH, also including dopaminergic and serotonergic stimulation, but it should also be noted that a trial with VH as the primary outcome has rarely been performed. This evidence concerns the gene BCHE and Parkinson disease.