C9orf72 and amyotrophic lateral sclerosis: While less data is currently available regarding the fate of synapses in sporadic ALS, given that C9orf72 mutations represent the most common genetic basis of both sporadic and familial ALS and since three out of five C9orf72 patients used in this study had no family history of ALS, our findings may be applicable to both familial and sporadic cases.