The UGT1A1 gene encodes an enzyme responsible for conjugation of bilirubin in the liver. Variants in UGT1A1 can impair this process, resulting in mild unconjugated hyperbilirubinaemia in the absence of liver disease or overt haemolysis; this is referred to as Gilbert syndrome. A specific mutation (described as the UGT1A1*28 allele) is a common cause of Gilbert syndrome in non-Asian populations. Gilbert syndrome due to the UGT1A1*28 allele is inherited in an autosomal recessive fashion.
Conjugation is also an important step in elimination of drugs. Individuals with Gilbert syndrome may have increased susceptibility to adverse effects of some drugs metabolised by UGT1A1, such as indinavir, atazanavir and irinotecan.
The presence of unconjugated hyperbilirubinaemia and two UGT1A1*28 alleles is required for a diagnosis of Gilbert syndrome. The diagnosis of Gilbert syndrome can be helpful in avoiding the pursuit of other more serious causes of elevated bilirubin (hyperbilirubinaemia).
The presence of two UGT1A1*28 alleles (irrespective of hyperbilirubinaemia) increases the risk of an adverse reaction to some drugs e.g. indinavir, atazanavir and irinotecan.
If used as a pharmacogenomic test, this test has a role in identifying patients who may benefit from avoiding a specific drug or dose, but it provides little useful information for people (including relatives) who are not taking the medications of concern. Testing of relatives is generally not recommended.
If used as a diagnostic test for Gilbert syndrome, the test result is unlikely to be clinically signicant for relatives.
Analysis of the UGT1A1 gene for *28, *36 and *37 allele variants.
Requesting the test
This test can be requested by any medical practitioner.
4 mL blood in EDTA. Specimens may be collected by the requesting practitioner or at any Sonic Healthcare collection centre (see link below).
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We recommend that the patient or another adult check the labelling of request forms and sample tubes.