| Hereditary hyperbilirubinemia | |
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| Bilirubin levels are increased by this condition | |
| Specialty | Endocrinology  |
Hereditary hyperbilirubinemia refers to the condition where levels of bilirubin are elevated, for reasons that can be attributed to a metabolic disorder.
An example is Crigler–Najjar syndrome.
UGT1A1 gene mutations causes the condition. As a result, there can be reduced functionality of the bilirubin-UGT enzyme. Eventually it causes unconjugated hyperbilirubinemia and jaundice as substance accumulates in the body due to the reduced ability of the enzyme. [1]
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Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and whites of the eyes due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme metabolism, liver dysfunction, or biliary-tract obstruction. The prevalence of jaundice in adults is rare, while jaundice in babies is common, with an estimated 80% affected during their first week of life. The most commonly associated symptoms of jaundice are itchiness, pale feces, and dark urine.
Bilirubin (BR) is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the destruction of aged or abnormal red blood cells. First the hemoglobin gets stripped of the heme molecule which thereafter passes through various processes of porphyrin catabolism, depending on the part of the body in which the breakdown occurs. For example, the molecules excreted in the urine differ from those in the feces. The production of biliverdin from heme is the first major step in the catabolic pathway, after which the enzyme biliverdin reductase performs the second step, producing bilirubin from biliverdin.
Liver function tests, also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated Partial Thromboplastin Time (aPTT), albumin, bilirubin, and others. The liver transaminases aspartate transaminase and alanine transaminase are useful biomarkers of liver injury in a patient with some degree of intact liver function. Most liver diseases cause only mild symptoms initially, but these diseases must be detected early. Hepatic (liver) involvement in some diseases can be of crucial importance. This testing is performed on a patient's blood sample. Some tests are associated with functionality, some with cellular integrity, and some with conditions linked to the biliary tract. Because some of these tests do not measure function, it is more accurate to call these liver chemistries or liver tests rather than liver function tests. Several biochemical tests are useful in the evaluation and management of patients with hepatic dysfunction. These tests can be used to detect the presence of liver disease, distinguish among different types of liver disorders, gauge the extent of known liver damage, and monitor the response to treatment. Some or all of these measurements are also carried out on those individuals taking certain medications, such as anticonvulsants, to ensure that the medications are not adversely impacting the person's liver.
Kernicterus is a bilirubin-induced brain dysfunction. The term was coined in 1904 by Schmorl. Bilirubin is a naturally occurring substance in the body of humans and many other animals, but it is neurotoxic when its concentration in the blood is too high, a condition known as hyperbilirubinemia. Hyperbilirubinemia may cause bilirubin to accumulate in the grey matter of the central nervous system, potentially causing irreversible neurological damage. Depending on the level of exposure, the effects range from clinically unnoticeable to severe brain damage and even death.
Gilbert syndrome (GS) is a syndrome in which the liver of affected individuals processes bilirubin more slowly than the majority. It confers significant health benefits. Many people never have symptoms. Occasionally a slight yellowish color of the skin or whites of the eyes may occur.
Neonatal jaundice is a yellowish discoloration of the white part of the eyes and skin in a newborn baby due to high bilirubin levels. Other symptoms may include excess sleepiness or poor feeding. Complications may include seizures, cerebral palsy, or kernicterus.
Dubin–Johnson syndrome is a rare, autosomal recessive, benign disorder that causes an isolated increase of conjugated bilirubin in the serum. Classically, the condition causes a black liver due to the deposition of a pigment similar to melanin. This condition is associated with a defect in the ability of hepatocytes to secrete conjugated bilirubin into the bile, and is similar to Rotor syndrome. It is usually asymptomatic, but may be diagnosed in early infancy based on laboratory tests. No treatment is usually needed.
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. The disorder is inherited in an autosomal recessive manner. The annual incidence is estimated at 1 in 1 000 000.
Uridine 5'-diphospho-glucuronosyltransferase is a microsomal glycosyltransferase that catalyzes the transfer of the glucuronic acid component of UDP-glucuronic acid to a small hydrophobic molecule. This is a glucuronidation reaction.
Rotor syndrome is a rare cause of mixed direct (conjugated) and indirect (unconjugated) hyperbilirubinemia, relatively benign, autosomal recessive bilirubin disorder characterized by non-hemolytic jaundice due to the chronic elevation of predominantly conjugated bilirubin.
Lucey–Driscoll syndrome is an autosomal recessive metabolic disorder affecting enzymes involved in bilirubin metabolism. It is one of several disorders classified as a transient familial neonatal unconjugated hyperbilirubinemia.
UDP-glucuronosyltransferase 1-1 also known as UGT-1A is an enzyme that in humans is encoded by the UGT1A1 gene.
In medicine, bilirubinuria is an abnormality in which conjugated bilirubin is detected in the urine.
UDP-glucuronosyltransferase 1-6 is an enzyme that in humans is encoded by the UGT1A6 gene.
UDP-glucuronosyltransferase 1-4 is an enzyme that in humans is encoded by the UGT1A4 gene.
6-Phosphogluconate dehydrogenase deficiency, or partial deficiency, is an autosomal hereditary disease characterized by abnormally low levels of 6-phosphogluconate dehydrogenase (6PGD), a metabolic enzyme involved in the Pentose phosphate pathway. It is very important in the metabolism of red blood cells (erythrocytes). 6PDG deficiency affects less than 1% of the population, and studies suggest that there may be race variant involved in many of the reported cases. Although it is similar, 6PDG deficiency is not linked to glucose-6-phosphate dehydrogenase (G6PD) deficiency, as they are located on different chromosomes. However, a few people have had both of these metabolic diseases.
Cholestatic pruritus is the sensation of itch due to nearly any liver disease, but the most commonly associated entities are primary biliary cholangitis, primary sclerosing cholangitis, obstructive choledocholithiasis, carcinoma of the bile duct, cholestasis, and chronic hepatitis C viral infection and other forms of viral hepatitis.
UDP-glucuronosyltransferase 1-9 is an enzyme that in humans is encoded by the UGT1A9 gene.
Ida Stephens Owens was an American scientist known for her work with drug-detoxifying enzymes. She received her Ph.D from Duke University in 1967, making her one of the first two African Americans to receive a doctorate from the school. She spent her career at the National Institutes of Health (NIH), where she worked from 1968 to 2017 and pioneered the study of the genetics of human diseases and drug metabolism.
Bilirubin glucuronide is a water-soluble reaction intermediate over the process of conjugation of indirect bilirubin. Bilirubin glucuronide itself belongs to the category of conjugated bilirubin along with bilirubin di-glucuronide. However, only the latter one is primarily excreted into the bile in the normal setting.
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