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Disease Profile

Crigler-Najjar syndrome type 2

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Crigler-Najjar syndrome, type II; Crigler Najjar syndrome type 2; Arias syndrome


Congenital and Genetic Diseases; Digestive Diseases; Metabolic disorders


Crigler-Najjar syndrome type 2 (CN-2) is a rare disorder that causes elevated levels of bilirubin in the blood (hyperbilirubinemia). Bilirubin normally is made by the body when old red blood cells are broken down. However, people with CN-2 develop hyperbilirubinemia even when red blood cells are not excessively broken down, because they have too little of a liver enzyme needed for conversion and excretion of bilirubin.[1][2][3]

The main symptom of CN-2 is persistent jaundice, which is yellowing of the skin, mucous membranes and whites of the eyes. Jaundice may become noticeable in infancy (particularly when an infant is sick or has not eaten for an extended time), but some people with CN-2 are not diagnosed until adulthood. Rarely, a person with CN-2 may develop bilirubin encephalopathy (also called kernicterus), especially during illness, prolonged fasting, or while under anesthesia.[1][2][3]

CN-2 is caused by mutations in the UGT1A1 gene and inheritance is autosomal recessive. CN-2 responds to treatment with phenobarbital; however during an episode of severe hyperbilirubinemia, phototherapy may be needed. Not all people with CN-2 require treatment, but routine monitoring is still recommended.[1][2][4]

Of note, mutations in the UGT1A1 gene can alternatively cause other disorders, such as Crigler-Najjar syndrome type 1 (CN-1) and Gilbert syndrome. CN-1 is characterized by near or complete absence of enzyme activity (versus partial absence in type 2) and severe, life-threatening symptoms. Phenobarbitol treatment is ineffective for people with CN-1, which is treated differently.[1][2][3] Gilbert syndrome is considered a mild liver disorder that often does not cause symptoms or causes mild jaundice.[2][5] Sometimes it can be hard to distinguish between Gilbert syndrome and CN-2 because of considerable overlap in measured bilirubin levels. Genetic testing to identify the specific mutation present is sometimes needed for the correct diagnosis.[5]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Neonatal hyperbilirubinemia
Prolonged neonatal jaundice
Prolonged yellowing of skin in newborn
Unconjugated hyperbilirubinemia
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance
Yellow skin
Yellowing of the skin

[ more ]



Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • Orphanet lists international laboratories offering diagnostic testing for this condition.


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Organizations Providing General Support

        Learn more

        These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

        Where to Start

        • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
        • Genetics Home Reference (GHR) contains information on Crigler-Najjar syndrome type 2. This website is maintained by the National Library of Medicine.
        • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

          In-Depth Information

          • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
          • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
          • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
          • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
          • PubMed is a searchable database of medical literature and lists journal articles that discuss Crigler-Najjar syndrome type 2. Click on the link to view a sample search on this topic.

            Selected Full-Text Journal Articles


              1. Crigler Najjar Syndrome. National Organization for Rare Disorders (NORD). 2016; https://rarediseases.org/rare-diseases/crigler-najjar-syndrome/.
              2. Gilbert Syndrome. National Organization for Rare Disorders (NORD). 2015; https://rarediseases.org/rare-diseases/gilbert-syndrome/.
              3. Crigler-Najjar syndrome. Genetics Home Reference (GHR). February, 2012; https://ghr.nlm.nih.gov/condition/crigler-najjar-syndrome.
              4. Roy-Chowdhury N, Roy-Chowdhury J. Crigler-Najjar syndrome. UpToDate. Waltham, MA: UpToDate; June 2, 2016; https://www.uptodate.com/contents/crigler-najjar-syndrome.
              5. Wagner K-H, Shiels RG, Lang CA, Khoei NS, Bulmer AC. Diagnostic criteria and contributors to Gilbert’s syndrome. Critical Reviews in Clinical Laboratory Sciences. 2018; 55(2):129-139. https://www.ncbi.nlm.nih.gov/pubmed/29390925.