(From Dr. Laville’s Heme Metabolism Handout, by Brian Buschman)
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Heme is synthesized from succinyl-CoA and glycine in a series of reactions that build larger and larger blocks. The key intermediate is d-ALA (d-aminoleunlinic acid). The synthesis of heme is controlled at the level of d-ALA by feedback from the amount of available heme.
Acute intermittent porphyria is an autosomal dominant trait involved in uroprphyrinogen synthase deficiency resulting in accumulation of d-ALA. It causes abdominal pain, constipation and CV changes. It is treated with hematin.
Porphyria cutanea tarda is the most common porphyria and is due to a deficiency of proporphyrinogen decarboxylase. It causes hypersensitivity to the sun so patients must avoid sunlight.
Lead in the body causes shortages of heme and increased excretion of heme products in the urine.
Heme is degraded to bilirubin which is conjugated with glucuronic acid and excreted. Jaundice results when the level of unexcreted bilirubin is high. It is common in chronic liver disease.
Gilbert’s syndromes is a slight rise in unconjugated bilirubin. It is a harmless condition that we need to worry about. Unless it appears on an old mini she probably won’t ask about it.
This one is due to a deficiency of hepatic glucoronyl transferase. The problem is that unconjugated bilirubin exceeds the binding capacity of albumin. It exists in both autosomal recessive and dominant forms.
Defective bilirubin excretion. Elevated plasma conjugated bilirubin levels are detectible in the urine. The liver becomes pigmented.
Defective bilirubin excretion but the liver is not pigmented. I guess if she wants to be anal she might test if we know the difference between Dubin-Johnson and Rotor syndromes being that in Dubin-Johnson the liver is pigmented and in Rotor it is not.
Cholestasis is the obstruction of flow through the biliary duct. It may occur in the liver or in the duct system. It results in dark urine, pale stools and itching due to deposits of bilirubin in the skin.
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