C9orf72 and early-onset autosomal dominant Alzheimer disease: Interestingly, recent studies showed that C9orf72 hexanucleotide repeat expansions also exist in Alzheimer's disease and other neurodegenerative disorders (Majounie et al., 2012), providing evidence that the etiology of various aging‐related neurodegenerative diseases involves common molecular mechanism associated with C9orf72. Expanded C9orf72 hexanucleotide RNA repeats can form RNA foci and sequester RNA‐binding proteins and therefore may cause neurodegeneration through RNA toxicity.