Gilbert syndrome (Real-Time PCR)
5 days Gilbert Syndrome
Gilbert syndrome is a relatively mild condition characterized by periods of elevated bilirubin levels in the blood (hyperbilirubinemia). Bilirubin is produced when red blood cells are broken down. This substance is eliminated from the body only after it undergoes a chemical reaction in the liver, which converts the toxic form of bilirubin (unconjugated bilirubin) into a non-toxic form called conjugated bilirubin.
People with Gilbert syndrome have an accumulation of unconjugated bilirubin in their blood (unconjugated hyperbilirubinemia). In affected individuals, bilirubin levels fluctuate and only rarely rise high enough to cause jaundice, which results in yellowing of the skin and the whites of the eyes.
Gilbert syndrome is usually diagnosed during adolescence. When individuals with this condition experience episodes of hyperbilirubinemia, these episodes are typically mild and usually occur when the body is under stress—such as dehydration, prolonged fasting, illness, intense exercise, or menstruation. Some individuals with Gilbert syndrome may also experience abdominal discomfort or fatigue. However, around 30% of people with Gilbert syndrome show no signs or symptoms, and the condition is discovered only when routine blood tests reveal elevated levels of unconjugated bilirubin.
Its prevalence is approximately 5%. The condition is caused by a decreased activity of the liver enzyme uridine diphosphate-glucuronosyltransferase (UGT1A1). The gene UGT1A1, which encodes this enzyme, has a promoter region in which the number of TA repeats is normally no more than 6. If there are 7 (in rare cases, 8) TA repeats in either a homozygous or heterozygous state, the functional activity of the UGT1A1 enzyme is reduced—this reduction is a necessary condition for the development of Gilbert syndrome.
In individuals with a homozygous mutation, the disease is associated with higher baseline bilirubin levels and more pronounced clinical manifestations. In heterozygous carriers, the condition typically remains latent.
Normally, as red blood cells break down, indirect (unconjugated) bilirubin is released and needs to be eliminated from the body. Once inside liver cells, bilirubin binds to glucuronic acid under the action of the UGT1A1 enzyme. The combination of bilirubin and glucuronic acid makes it water-soluble, which allows it to be excreted into bile and eliminated through urine.
Due to the UGT1A1 gene mutation and therefore insufficient UGT1A1 enzyme activity, the conjugation of indirect bilirubin is impaired. This leads to increased levels of unconjugated bilirubin in the blood. In turn, elevated bilirubin levels contribute to its accumulation in tissues—particularly elastic tissues such as blood vessel walls, skin, and sclera—which explains the occurrence of jaundice.
When is Genetic Testing for Gilbert Syndrome Recommended?
- When Gilbert syndrome is suspected
- For differential diagnosis between Gilbert syndrome and other diseases that manifest with hyperbilirubinemia
- Due to the high prevalence of Gilbert syndrome, genetic testing is recommended prior to treatments involving hepatotoxic medications
- For assessing the risk of complications during treatment with irinotecan (a chemotherapy drug)
- In cases of mild, non-infectious jaundice
- When the patient has chronic jaundice treated with barbiturates
- When bilirubin levels are elevated, but other biochemical parameters are normal
- Family history of non-infectious jaundice or hyperbilirubinemia.
IMPORTANT NOTE:
Sample collected: Venous blood
Preparation: The sample must be collected on an fasting. The last meal should be consumed at least 2–3 hours before the sample is taken.
Method: Real-Time PCR
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