C9orf72 and Parkinson disease: Research into familial variants and other genetic predispositions leading to neurodegeneration (e.g., hexanucleotide repeat expansion mutations in the promoter region of C9orf72, known to drive the ALS pathology; SCA2 and SCA3 expansion mutations, LRRK2 mutations, and single-nucleotide polymorphisms (SNPs) in SNCA, MAPT, and GBA genes possibly driving PD pathogenesis; and SNPs in APOE, widely known to drive AD pathology) assists in understanding mechanisms of disease progression [91], and could be leveraged in assisting diagnosis using scales such as polygenic risk scores (PRS) [92].