UGT1A1 and kernicterus: Other cases describe episodes of severe hyperbilirubinemia, leading to acute bilirubin encephalopathy and kernicterus.11,12 In addition, more than half of the Western population may be heterozygous carriers of the Gilbert-type promoter gene.2 We suspect that some patients may have combined UGT1A1 polymorphisms with 1 heterozygous missense allele and another heterozygous promoter variant in the other allele.