UGT1A1 and Gilbert syndrome: On the other hand, those with congenitally decreased expression of UGT1A1 (which is caused in the majority of Caucasians by homozygosity of the so-called UGT1A1∗28 allele) [24] results in mild unconjugated hyperbilirubinemia (Gilbert's syndrome), a condition associated with a decreased risk of cardiovascular diseases [21].