Crigler-Najjar Syndrome

Gene : UGT1A1

What is Crigler-Najjar syndrome?

Crigler-Najjar (CN) syndrome is a very rare inherited disorder caused by deficiency of the bilirubin uridine diphosphate glucuronosyl transferase (bilirubin-UGT) enzyme. Deficiency of the bilirubin-UGT enzyme results in high levels of a toxic form of bilirubin, a product of the breakdown of red blood cells. High levels of this bilirubin can cause kernicterus, a form of brain damage, which could lead to hearing problems or intellectual disability. Symptoms of affected children include yellowing of the skin, lack of energy, low muscle tone, and occasionally increased tightness of muscles. Symptoms are usually evident at birth or first weeks of life. There are two types of CN syndrome; CN1 and CN2. CN1 is very severe and death usually occurs in childhood. CN2 is less severe and affected individuals can generally survive into adulthood without any intellectual impairment. CN is caused by pathogenic variants in the UGT1A1 gene.

How is Crigler-Najjar syndrome inherited?

Crigler-Najjar syndrome is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for CN syndrome. However, the risk to have a child affected with CN syndrome is increased. Testing of reproductive partners is recommended for carriers of CN syndrome.

How common is Crigler-Najjar syndrome?

Crigler-Najjar syndrome is a very rare condition that affects all ethnicities. It is estimated to occur in 1 in 750,000 to 1 in 1,000,000 newborns in the general population.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems





Carrier Rates
Detection Rate
Carrier Frequency
General Population 94% 1 in 500

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