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The varied causes of hyperbilirubinemia are best understood from bilirubin metabolism. The total average daily production of bilirubin in humans is 4 mg/kg. 80% of which is derived from haemoglobin (Hb) produced by erythrocyte breakdown, with the remaining from heme proteins , like myoglobin and cytochrome , turnover. [ 5 ]
Rotor syndrome (also known as Rotor type hyperbilirubinemia) [2] is a rare cause of mixed direct (conjugated) and indirect (unconjugated) hyperbilirubinemia, relatively benign, autosomal recessive [3] bilirubin disorder characterized by non-hemolytic jaundice due to the chronic elevation of predominantly conjugated bilirubin. [2]
Prehepatic causes are associated mostly with an increase of unconjugated (indirect) bilirubin. [21] They include: Hemolysis or increased breakdown of red blood cells (for example hematoma resorption) Intrahepatic causes can be associated with elevated levels of conjugated bilirubin, unconjugated bilirubin or both. [21] They include: [21]
Gilbert syndrome is a phenotypic effect, mostly associated with increased blood bilirubin levels, but also sometimes characterized by mild jaundice due to increased unconjugated bilirubin, that arises from several different genotypic variants of the gene for the enzyme responsible for changing bilirubin to the conjugated form. [citation needed]
Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and sclera due to high bilirubin levels. [3] [6] Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme metabolism, liver dysfunction, or biliary-tract obstruction. [7]
There are additional rare causes of hereditary hyperbilirubinemia like Lucey-Driscoll syndrome and Heme Oxygenase-1 Deficiency. [1] Both Gilbert syndrome and Crigler-Najjar syndrome cause an elevated unconjugated bilirubin level due to mutations in the UGT1A1 gene, which conjugates bilirubin within liver cells so it can be excreted.
When total bilirubin levels exceed 40 μmol/L, bilirubin deposition at the sclera, skin, and mucous membranes will give these areas a yellow colour, thus it is called jaundice. [6] The increase in predominantly unconjugated bilirubin is due to overproduction, reduced hepatic uptake of the unconjugated bilirubin and reduced conjugation of bilirubin.
Crigler–Najjar syndrome is a rare inherited disorder affecting the metabolism of bilirubin, a chemical formed from the breakdown of the heme in red blood cells. The disorder results in a form of nonhemolytic jaundice, which results in high levels of unconjugated bilirubin and often leads to brain damage in infants.