gut liver transplantation before the onset of brain damage and before phototherapy becomes ineffective at later age Type II The inheritance patterns of both Crigler–Najjar syndrome types I and II are autosomal recessive. However, type II differs from type I in a number of different aspects: Bilirubin levels are generally below 345 μmol/L [20 mg/dL] (range 100–430 μmol/L [6–24 mg/dL]; thus, overlap may sometimes occur), and some cases are only detected later in life. Because of lower serum bilirubin, kernicterus is rare in type II. Bile is pigmented, instead of pale in type I or dark as normal, and monoconjugates constitute the largest fraction of bile conjugates. UGT1A1 is present at reduced but detectable levels (typically <10% of normal), because of single base pair mutations. Therefore, treatment with phenobarbital is effective, generally with a decrease of at least 25% in serum bilirubin. In fact, this can be used, along with these other factors, to differentiate type I and II. Differential diagnosis Neonatal jaundice may develop in the presence of sepsis, hypoxia, hypoglycemia, hypothyroidism, hypertrophic pyloric stenosis, galactosemia, fructosemia, etc. Hyperbilirubinemia of the unconjugated type may be caused by: increased production hemolysis (e.g., hemolytic disease of the newborn, hereditary spherocytosis, sickle cell disease) ineffective erythropoiesis massive tissue necrosis or large hematomas decreased clearance drug-induced physiological neonatal jaundice and prematurity liver diseases such as advanced hepatitis or cirrhosis breast milk jaundice and Lucey–Driscoll syndrome Crigler–Najjar syndrome and Gilbert syndrome In Crigler–Najjar syndrome and Gilbert syndrome, routine liver function tests are normal, and hepatic histology usually is normal, too. No evidence for hemolysis is seen. Drug-induced cases typically regress after discontinuation of the substance. Physiological neonatal jaundice may peak at 85–170 μmol/L and decline to normal adult concentrations within two weeks. Prematurity results in higher levels. Treatment Plasmapheresis and phototherapy are used for treatment. Liver transplant is curative. Research A San Francisco-based company named Audentes Therapeutics is currently investigating the treatment of Crigler–Najjar syndrome with one of their gene replacement therapy products, AT342. Preliminary success has been found in early stages of a phase 1/2 clinical trial. One 10-year-old girl with Crigler–Najjar syndrome type I was successfully treated by liver cell transplantation. The homozygous Gunn rat, which lacks the enzyme uridine diphosphate glucuronyltransferase (UDPGT), is an animal model for the study of Crigler–Najjar syndrome. Since only one enzyme is working improperly, gene therapy for Crigler-Najjar is a theoretical option which is being investigated.