C9 and amyotrophic lateral sclerosis: In C9-ALS iPSCs, the mean normalized values for introns 1 and 2 were 3.1 and 2.7 times higher than control iPSCs, respectively (S4 Table and Fig 3A, p = 6e-06 and 0.0002, respectively), while no significant accumulation was observed in other introns (Fig 3A).