Higher neurofilament light chain protein in CSF, a lower hippocampal volume and more non-motor symptoms such as depression and RBD have been also identified as risk factors for faster cognitive decline.126 Moreover, genetic risk factors include variants in the GBA gene, multiplications in the α-synuclein gene (SNCA), H1 haplotype of the MAPT gene and carrying the APOE 4 allele.120 In line with this, risk factors for conversion to PD dementia also include the APOE 4 allele, mutations in the GBA gene and reduced levels of amyloid beta 42 in the CSF.127. This evidence concerns the gene APOE and major depressive disorder.