▁sympt om atic ▁people ▁did ▁not ▁confirm ▁their ▁effic acy . ▁Another ▁clin ical ▁trial ▁in ▁pre - sym pt om atic ▁types ▁ 1 – 2 ▁inf ants ▁was ▁completed ▁in ▁ 2 0 1 5 ▁but ▁no ▁results ▁have ▁been ▁published . ▁ ▁Val pro ic ▁acid ▁( V PA ) ▁was ▁used ▁in ▁S MA ▁on ▁an ▁experimental ▁basis ▁in ▁the ▁ 1 9 9 0 s ▁and ▁ 2 0 0 0 s ▁because ▁in ▁vit ro ▁research ▁suggested ▁its ▁moder ate ▁effect iveness . ▁However , ▁it ▁demonstrated ▁no ▁effic acy ▁in ▁achiev able ▁concentr ations ▁when ▁subject ed ▁to ▁a ▁large ▁clin ical ▁trial . ▁ ▁It ▁has ▁also ▁been ▁proposed ▁that ▁it ▁may ▁be ▁effective ▁in ▁a ▁subset ▁of ▁people ▁with ▁S MA ▁but ▁its ▁action ▁may ▁be ▁suppress ed ▁by ▁fat ty ▁acid ▁trans loc ase ▁in ▁others . ▁O thers ▁argue ▁it ▁may ▁actually ▁ag gra v ate ▁S MA ▁sympt oms . ▁It ▁is ▁currently ▁not ▁used ▁due ▁to ▁the ▁risk ▁of ▁severe ▁side ▁effects ▁related ▁to ▁long - term ▁use . ▁A ▁ 2 0 1 9 ▁meta - analysis ▁suggested ▁that ▁V PA ▁may ▁offer ▁benefits , ▁even ▁without ▁impro ving ▁functional ▁score . ▁ ▁H ydro xy car b am ide ▁( h ydro xy ure a ) ▁was ▁shown ▁effective ▁in ▁mouse ▁models ▁and ▁subsequently ▁commer cially ▁research ed ▁by ▁Nov o ▁Nord isk , ▁Den mark , ▁but ▁demonstrated ▁no ▁effect ▁on ▁people ▁with ▁S MA ▁in ▁subsequent