GRN and amyotrophic lateral sclerosis: Although underlying TDP-43 pathology does not always correlate with genetics or disease phenotype, mutations to 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 type B pathology (Mackenzie et al., 2011; Boeve et al., 2012).