Previous in vitro studies have shown that sodium 4-phenylbutyrate (4-PB), a European Medicines Agency (EMA)- and Food Drug Administration (FDA)-approved butyrate analog used as an ammonia scavenger in patients with urea cycle disorders (UCDs), was able to increase cell surface/canalicular expression of some ABCB11 missense variants, including E297G, D404G, D482G, G982R, R1128C, T1210P and R1231Q [9,11,13,14,15], as well as of wild type (wt) ABCB11 [13,14,15]. This evidence concerns the gene ABCB11 and urea cycle disorder.