PRKN and Parkinson disease: Some recent studies also focused on modeling non-motor symptoms of PD in flies carrying loss-of-function mutations in PINK1 and Parkin, revealing that both mutant genotypes displayed reduced learning and memory performances, as well as a weakening of circadian rhythms, suggesting novel mechanisms of action of these disease-causing genes and providing support for the idea that cognitive and circadian dysregulation is an intrinsic aspect of PD rather than a side effect of medication or linked to environmental factors [120].