HDAC9 and urea cycle disorder: In addition to inhibiting farnesylation of p21ras and geranylgeranylation of p21rac, NaPB exhibits many other biological functions including histone deacetylase (HDAC) inhibition [40], chemical chaperoning upon endoplasmic reticulum (ER) stress [41] and ammonia scavenging in urea cycle disorders [42], which could be responsible for the protection of nigrostriatum from MPTP neurotoxicity.