C9orf72 and amyotrophic lateral sclerosis: C9ORF72 HRE-positive ALS causes typical TAR DNA-binding protein 43 (TDP-43) positive pathology but also results in a reduction in C9ORF72 transcript levels, accumulation of repeat RNA in intracellular foci, and inclusions of dipeptide protein aberrantly translated from the hexanucleotide RNA.