C9orf72 and amyotrophic lateral sclerosis: Although the underlying TDP-43 pathology does not always correlate with the genetics or disease phenotype, mutations of the progranulin (GRN) gene are generally associated with type A TDP-43 pathology, whereas hexanucleotide repeat expansions in C9orf72, which is the most common genetic cause of ALS and FTLD-TDP, most frequently result in the type B pathology [29,30].