In the intercostal muscles, which generate expiratory flow, the mRNA expression levels of MYH1 and MYH2, encoding MHC type IIx and IIa, respectively, but not MYH7, were significantly decreased in samples from SBMA subjects compared with ALS subjects, strengthening the theory that fast muscle power is predominantly affected in SBMA (Fig 5A–5C). Here, MYH1 is linked to amyotrophic lateral sclerosis.