In the literature, a possible modifier effect on GBA has been reported for variants in the cathepsin B (CTSB) and alpha-synuclein (SNCA) genes, common variants in the proximity of the GBA gene, GBA pseudogene 1 (GBAP1), Metaxin 1 (MTX1) and Bridging Integrator 1 (BIN1) genes, as well as the leucine repeat rich kinase 2 (LRRK2), the other major genetic risk factor of PD [18–24]. Here, MTX1 is linked to Parkinson disease.