An inherited condition (usually autosomal recessive) called Gilbert’s Syndrome (GS) causes unconjugated hyperbilirubinemia, i.e. elevated unconjugated or indirect bilirubin and total bilirubin. An enzyme called uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) is responsible for the conjugation of bilirubin in the liver, i.e. takes indirect or unconjugated bilirubin and conjugates it into conjugated or direct bilirubin, which can then be excreted in the bile. Patients with Gilbert’s syndrome have a defect in the gene that encodes for the conjugating enzyme. The result of which is somewhere between 60 – 70% reduction in the ability of the liver to conjugate bilirubin.
I did come across this article that seems to make a connection between this conjugating enzyme and Celiac disease:
https://www.ncbi.nlm.nih.gov/pubmed?Db=pubmed&Cmd=DetailsSearch&Term=16393303