Which hyperbilirubinemia form is caused by an inherited absence of UDP-glucuronyl transferase?

Crigler-Najjar syndrome is characterized by a specific genetic deficiency in the enzyme UDP-glucuronyl transferase, which is responsible for the conjugation of bilirubin in the liver. This deficiency results in the accumulation of unconjugated bilirubin in the bloodstream, leading to severe hyperbilirubinemia. There are two main types of Crigler-Najjar syndrome: Type 1, which is a complete absence of the enzyme and presents with very high levels of unconjugated bilirubin, and Type 2, which has a partial deficiency. The severe form typically presents in infancy and requires prompt treatment to prevent kernicterus, a serious condition associated with high levels of unconjugated bilirubin.

In contrast, other options involve different mechanisms or types of bilirubin metabolism issues. For instance, Gilbert's syndrome involves a reduced function of UDP-glucuronyl transferase but not a complete absence, leading to mild unconjugated hyperbilirubinemia. Rotor syndrome, similar to Dubin-Johnson syndrome, involves issues with conjugated (direct) bilirubin but does not stem from an absence of the enzyme; instead, these syndromes are related to other factors affecting bilirubin excretion. Thus, the