Final answer:
Crigler-Najjar syndrome type I is a severe inherited condition caused by a lack of UDP glucuronyl transferase activity, resulting in high serum bilirubin levels and a risk of brain damage. It differs significantly from type II and Gilbert's disease, which are less severe and involve different issues with bilirubin metabolism.
Step-by-step explanation:
Crigler-Najjar Syndrome Type I
Crigler-Najjar syndrome type I is a rare inherited liver disorder characterized by high levels of unconjugated bilirubin. This occurs due to the absence of the enzyme UDP glucuronyl transferase activity in the liver cells. This enzyme is crucial for the conjugation of bilirubin, which is necessary for the bilirubin to be dissolved in bile and excreted from the body. In individuals with type I, the serum bilirubin level often exceeds 20 mg/dl, which can lead to severe jaundice and a risk of brain damage, known as kernicterus. In contrast, Crigler-Najjar syndrome type II is less severe. This type's liver can form bilirubin monoglucuronide, but it cannot be further glucuronated, which is also due to the absence of UDP glucuronyl transferase-II.
Additionally, Gilbert's disease is another condition that involves bilirubin metabolism. In Gilbert's disease, there is a lowered UDP-glucuronyl transferase activity, which leads to a defect in the uptake of bilirubin by the liver.