Hereditary or inborn metabolic disorders may cause unconjugated or conjugated hyperbilirubinemia (see Overview of bilirubin metabolism Overview of bilirubin metabolism The liver is a metabolically complex organ. Hepatocytes (liver parenchymal cells) perform the liver’s metabolic functions: Formation and excretion of bile as a component of bilirubin metabolism... read more ).
(See also Liver Structure and Function Liver Structure and Function The liver is a metabolically complex organ. Hepatocytes (liver parenchymal cells) perform the liver’s metabolic functions: Formation and excretion of bile as a component of bilirubin metabolism... read more and Evaluation of the Patient with a Liver Disorder Evaluation of the Patient With a Liver Disorder History and physical examination often suggest a cause of potential liver disorders and narrow the scope of testing for hepatic and biliary disorders. Various symptoms may develop, but few are... read more .)
This rare inherited liver disorder is caused by deficiency of the enzyme glucuronyl transferase (UGT1A1), which catalyzes the conjugation of bilirubin (mainly to bilirubin diglucuronide) to render bilirubin water soluble. Various defects in the gene coding for the enzyme cause complete (type 1) or partial (type 2) inactivation of the enzyme.
Patients with autosomal recessive type I (complete) disease have severe unconjugated hyperbilirubinemia typically beginning shortly after birth. They usually die of kernicterus Kernicterus Kernicterus is brain damage caused by unconjugated bilirubin deposition in basal ganglia and brain stem nuclei. Normally, bilirubin bound to serum albumin stays in the intravascular space. However... read more by age 1 year but may survive into adulthood. Treatment may include phototherapy and liver transplantation Liver Transplantation Liver transplantation is the 2nd most common type of solid organ transplantation. (See also Overview of Transplantation.) Indications for liver transplantation include Cirrhosis (70% of transplantations... read more .
Patients with autosomal recessive type II (partial) disease (which has variable penetrance) often have less severe unconjugated hyperbilirubinemia (< 20 mg/dL [< 342 micromol/L]) and usually live into adulthood without neurologic damage. Phenobarbital 1.5 to 2 mg/kg orally 3 times/day, which induces the partially deficient glucuronyl transferase, may be effective.
Dubin-Johnson syndrome and Rotor syndrome cause conjugated hyperbilirubinemia, but without cholestasis, causing no symptoms or sequelae other than jaundice. Bilirubin may appear in the urine, in contrast to the unconjugated hyperbilirubinemia in Gilbert syndrome Gilbert Syndrome Hereditary or inborn metabolic disorders may cause unconjugated or conjugated hyperbilirubinemia (see Overview of bilirubin metabolism). Unconjugated hyperbilirubinemia: Crigler-Najjar syndrome... read more (which also causes no other symptoms), in which bilirubin is absent from the urine. Aminotransferase and alkaline phosphatase levels are usually normal. Treatment is unnecessary.
This rare autosomal recessive disorder involves impaired excretion of bilirubin glucuronides. It is usually diagnosed by liver biopsy Liver Biopsy Liver biopsy provides histologic information about liver structure and evidence of liver injury (type and degree, any fibrosis); this information can be essential not only to diagnosis but also... read more ; the liver is deeply pigmented as a result of an intracellular melanin-like substance but is otherwise histologically normal.
Gilbert syndrome is a presumably lifelong disorder in which the only significant abnormality is asymptomatic, mild, unconjugated hyperbilirubinemia. It can be mistaken for chronic hepatitis or other liver disorders.
Gilbert syndrome may affect as many as 5% of people. Although family members may be affected, a clear genetic pattern is difficult to establish.
Pathogenesis may involve complex defects in the liver’s uptake of bilirubin. Glucuronyl transferase activity is low, though not as low as in Crigler-Najjar syndrome Crigler-Najjar Syndrome Hereditary or inborn metabolic disorders may cause unconjugated or conjugated hyperbilirubinemia (see Overview of bilirubin metabolism). Unconjugated hyperbilirubinemia: Crigler-Najjar syndrome... read more type II. In many patients, red blood cell destruction is also slightly accelerated, but this acceleration does not cause anemia or hyperbilirubinemia. Liver histology is normal.
Gilbert syndrome is most often detected in young adults serendipitously by finding an elevated bilirubin level, which usually fluctuates between 2 and 5 mg/dL (34 and 86 micromol/L) and tends to increase with fasting and other stresses.
Gilbert syndrome is differentiated from hepatitis by fractionation that shows predominantly unconjugated bilirubin, otherwise normal liver test results, and absence of urinary bilirubin. It is differentiated from hemolysis by the absence of anemia and reticulocytosis.
Treatment is unnecessary. Patients should be reassured that they do not have liver disease.