HDAC9 and amyotrophic lateral sclerosis: Interestingly, 4-phenylbutyrate, a closely related compound to NaBut that is also an HDAC inhibitor, has been shown to promote survival in two models of chronic MN loss (Butchbach et al., 2016; Petri et al., 2006), while the combination of phenylbutyrate and taurursodiol significantly reduced functional decline in humans with ALS (Paganoni et al., 2020) and recently received U.S. Food and Drug Administration (FDA) approval (Aschenbrenner, 2023).