Diagnostic Test Directory

Molecular Genetics Laboratory

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Gilbert Syndrome (UGT1A1)

  • Synonyms: Hyperbilirubinemia I
  • LIS Mnemonic: MBGBS

    Collect

    Collect whole blood in a purple top (EDTA) tube.

    Volume Required

    5 ml

    Minimum Required

    3 ml

    Transport

    Refrigerate sample until shipment. Send the sample at room temperature with overnight delivery for receipt Monday through Friday within 24 hours of collection.

    Stability

    Whole blood can be refrigerated until shipment.

    Unacceptable conditions

    Heparinized specimens, severely hemolyzed specimens, frozen, clotted or possibly commingled specimens, blood in non-sterile or leaky containers, mislabeled or inappropriately labeled specimens.

    Specimen Handling

    Do not heat, freeze or centrifuge blood before shipment. Refrigerate sample until shipment.

Days Performed

Mon - Fri 9:00am to 4:00pm

Reported

2-3 weeks

CPT

81350

Disease Information

Clinical Features:

Gilbert’s syndrome, a common phenotype found in approximately 3-10% of the general population, is characterized by mild, chronic, unconjugated hyperbilirubinemia in the absence of liver disease or overt hemolysis. The diagnosis of this disorder is made on the observation of elevated unconjugated bilirubin levels and normal liver function. The importance of the diagnosis of this benign syndrome is to rule out more serious liver disease as the underlying cause of the hyperbilirubinemia. Individuals with Gilbert’s syndrome have a reduced level of hepatic bilirubin UDP-glucuronosyltransferase 1A1 (UGT1A1), the enzyme necessary for the conjugation of bilirubin.

Molecular Genetics:

The UGT1A1 gene is located on chromosome 2q37. A polymorphism in the promoter region of the UGT1A1 gene has been identified in the majority of Caucasian individuals with Gilbert’s syndrome (80-100%). Most individuals are homozygous for two extra bases (TA) in the promoter region of the gene and have an A(TA)7TAA sequence rather than an A(TA)6TAA sequence. This change is associated with reduced expression of the UGT1A1 gene. Other normal alleles with 5 TA repeats or abnormal alleles with 8 TA repeats have also been identified, although less commonly.

Test Methods:

We offer DNA sequence analysis of the promoter region of the UGT1A1 gene to detect all allele types. PCR amplification and sequencing is performed on the promoter region. The patient’s gene sequence is then compared to a reference sequence. Sequence variants are classified as A(TA)6TAA, A(TA)7TAA, A(TA)5TAA, and A(TA)8TAA.

Detection Rate:

The analytical sensitivity for sequencing is close to 100%. Approximately 98% of patients with Gilbert’s syndrome will be homozygous or compound heterozygotes for two abnormal TA repeat alleles.

Results:

Test results with interpretation will be mailed and/or faxed to the referring physician or send out lab following completion of the test. Additional reports will be provided as requested.

Utility:

Gilbert’s syndrome is considered benign in adults, although an incidental finding of hyperbilirubinemia may raise the possibility of liver disease and so trigger unnecessary investigational testing. Co-inheritance of Gilbert’s syndrome and a known hemolytic disorder such as sickle cell anemia may go undetected due to already high levels of unconjugated bilirubin in these patients. However, these patients are at increased risk for developing gallstones at an early age. Confirmation of Gilbert’s syndrome in these patients may lead to early intervention and treatment. Gilbert’s syndrome is also associated with a higher chance of developing severe diarrhea and leucopenia during irinotecan therapy. Irinotecan is a potent chemotherapeutic drug commonly used for many types of cancer, in particular, gastrointestinal and pulmonary malignancies. Its active metabolite, SN-38, is glucuronidated by UGT1A1. The presence of the 7/7 genotype in UGT1A1 can lead to a 1.8-3.9 lower glucuronidation of SN-38 compared with patients with the wild type (6/6) resulting in dose limiting toxicity of irinotecan. Determination of UGT1A1 genotypes will aid in identifying those patients who have an increased risk of developing toxicity phenotypes with irinotecan treatment.

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