hereditary hyperbilirubinemia hereditary hyperbilirubinemia hereditary hyperbilirubinemia refers to the condition where levels of bilirubin are elevated, for reasons that can be attributed to a metabolic disorder. hereditary hyperbilirubinemiabilirubin levels are increased by this conditionspecialtyendocrinology an example is crigler–najjar syndrome. symptoms and signs ugt1a1 gene mutations causes the condition. as a result, there can be reduced functionality of the bilirubin-ugt enzyme. eventually it causes unconjugated hyperbilirubinemia and jaundice as substance accumulates in the body due to the reduced ability of the enzyme. diagnosis