Crigler–Najjar syndrome is a rare inherited disorder affecting the metabolism of bilirubin, a chemical formed from the breakdown of the heme in red blood cells. The disorder results in a form of nonhemolytic jaundice, which results in high levels of unconjugated bilirubin and often leads to brain damage in infants. The disorder is inherited in an autosomal recessive manner. The annual incidence is estimated at 1 in 1,000,000. This syndrome is divided into types I and II, with the latter sometimes called Arias syndrome. These two types, along with Gilbert's syndrome, Dubin–Johnson syndrome, and Rotor syndrome, make up the five known hereditary defects in bilirubin metabolism. Unlike Gilbert's syndrome, only a few causes of Crigler–Najjar syndrome are known. Signs and symptoms Signs and symptoms of Crigler-Najjar syndrome include Jaundice, diarrhea, vomiting, fever, confusion, slurred speech, difficulty swallowing, change in gait, staggering, frequent falling and seizures Cause It is caused by abnormalities in the gene coding for uridine diphosphoglucuronate glucuronosyltransferase (UGT1A1). UGT1A1 normally catalyzes the conjugation of bilirubin and glucuronic acid within hepatocytes. Conjugated bilirubin is more water-soluble and is excreted in bile. Diagnosis Type I This is a very rare disease (estimated at 0.6–1.0 per million live births), and consanguinity increases the risk of this condition (other rare diseases may be present). Inheritance is autosomal recessive. Intense jaundice appears in the first days of life and persists thereafter. Type 1 is characterised by a serum bilirubin usually above 345 μmol/L [20 mg/dL] (range 310–755 μmol/L [18–44 mg/dL]) (whereas the reference range for total bilirubin is 2–14 μmol/L [0.1–0.8 mg/dL]). No UDP glucuronosyltransferase 1-A1 expression can be detected in the liver tissue. Hence, there is no response to treatment with phenobarbital, which causes CYP450 enzyme induction. Most patients (type IA) have a mutation in one of the common exons (2 to 5), and have difficulties conjugating several additional substrates (several drugs and xenobiotics). A smaller percentage of patients (type IB) have mutations limited to the bilirubin-specific A1 exon; their conjugation defect is mostly restricted to bilirubin itself. Before the availability of phototherapy, these children died of kernicterus (bilirubin encephalopathy) or survived until early adulthood with clear neurological impairment. Today, therapy includes exchange transfusions in the immediate neonatal period 12 hours/day phototherapy heme oxygenase inhibitors to reduce transient worsening of hyperbilirubinemia (although the effect of the drug decreases over time) oral calcium phosphate and carbonate to form complexes with bilirubin in the