Old studies carried out on subjects with UGT gene polymorphisms have shown that these gene variations, despite being very common [54] and the cause of clinical syndromes with high unconjugated hyperbilirubinemia levels (i.e., Gilbert’s disease and Crigler–Najjar syndrome) [55], do not play a relevant role as a cause of drug clearance modification. The gene discussed is SLC35A2; the disease is Hyperbilirubinemia.