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Questions and Answers
Which enzyme defect is responsible for the accumulation of tetrapyrrole intermediates, leading to photosensitivity?
Which type of porphyria is characterized by abdominal pain, neuropsychiatric disturbances, and photosensitivity?
What is the primary site of accumulation of porphyrins or porphyrin precursors in erythropoietic porphyrias?
Which enzyme is responsible for the conversion of hydroxymethylbilane to uroporphyrinogen III?
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Which porphyria is characterized by abdominal pain and neuropsychiatric disturbances, but not photosensitivity?
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What is the primary site of accumulation of porphyrins or porphyrin precursors in hepatic porphyrias?
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Which enzyme is responsible for the final step of heme synthesis?
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What is the primary characteristic of chronic hepatic porphyrias?
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Which of the following statements about porphyrias is TRUE?
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What is the key distinction between acute hepatic porphyrias and chronic hepatic porphyrias?
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Which enzyme is involved in the conversion of hydroxymethylbilane to uroporphyrinogen III?
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What is the common feature of all hepatic porphyrias?
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Which of the following porphyrias is NOT characterized by abdominal pain?
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What is the final product of the heme synthetic pathway?
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Which of the following enzymes is involved in the conversion of coproporphyrinogen III to protoporphyrinogen?
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Which type of porphyria is characterized by the accumulation of porphyrins or porphyrin precursors in the liver?
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Study Notes
Heme Synthesis and Porphyrias
- Porphyrias are rare, inherited or acquired defects in heme synthesis, resulting in the accumulation and increased excretion of porphyrins or porphyrin precursors.
- Each porphyria results in the accumulation of intermediates caused by the deficiency of an enzyme in the heme synthetic pathway.
Classification of Porphyrias
- Erythropoietic porphyrias
- Hepatic porphyrias, which include:
- Acute hepatic porphyrias
- Chronic hepatic porphyrias
Clinical Manifestations of Porphyrias
- Enzyme deficiency prior to tetrapyrrole synthesis leads to abdominal and neuropsychiatric signs.
- Enzyme deficiency leading to accumulation of tetrapyrrole intermediates leads to photosensitivity.
Heme Synthesis Pathway Enzymes
- ALAS1 (ALA synthase)
- ALA dehydratase
- Hydroxymethylbilane synthase (HMBS)
- Uroporphyrinogen III synthase
- Uroporphyrinogen III decarboxylase
- Coproporphyrinogen III oxidase
- Protoporphyrinogen oxidase
- Ferrochelatase
Types of Porphyria
Hepatic Porphyrias
- Acute Intermittent Porphyria (AIP): deficiency of Hydroxymethylbilane synthase, characterized by abdominal pain and neuropsychiatric disturbances.
- Porphyria Cutanea Tarda (PCT): deficiency of Uroporphyrinogen III decarboxylase, characterized by photosensitivity.
- Hereditary Coproporphyria: deficiency of Coproporphyrinogen III oxidase, characterized by abdominal pain, neuropsychiatric disturbances, and photosensitivity.
- Variegate Porphyria (VP): deficiency of Protoporphyrinogen oxidase.
Heme Synthesis and Porphyrias
- Porphyrias are rare, inherited or acquired defects in heme synthesis, leading to the accumulation and increased excretion of porphyrins or porphyrin precursors.
- Each porphyria results from the deficiency of an enzyme in the heme synthetic pathway, causing the accumulation of intermediates.
Classification of Porphyrias
- Erythropoietic porphyrias
- Hepatic porphyrias, which are further divided into:
- Acute hepatic porphyrias
- Chronic hepatic porphyrias
Clinical Manifestations of Porphyrias
- If enzyme deficiency occurs before tetrapyrrole synthesis, abdominal and neuropsychiatric signs occur.
- If enzyme deficiency leads to tetrapyrrole intermediate accumulation, photosensitivity occurs.
Enzymes in Heme Synthesis
- ALAS1 (ALA synthase)
- ALA dehydratase
- Hydroxymethylbilane synthase (HMBS)
- Uroporphyrinogen III synthase
- Uroporphyrinogen III decarboxylase
- Coproporphyrinogen III oxidase
- Protoporphyrinogen oxidase
- Ferrochelatase
Types of Porphyrias
- Acute Intermittent Porphyria (AIP):
- Enzyme defect: Hydroxymethylbilane synthase
- Signs: Abdominal pain, neuropsychiatric disturbances
- Porphyria Cutanea Tarda (PCT):
- Enzyme defect: Uroporphyrinogen III decarboxylase
- Signs: Photosensitivity
- Hereditary Coproporphyria:
- Enzyme defect: Coproporphyrinogen III oxidase
- Signs: Abdominal pain, neuropsychiatric disturbances, photosensitivity
- Variegate Porphyria:
- Enzyme defect: Protoporphyrinogen oxidase
- Signs: Abdominal pain, neuropsychiatric disturbances, photosensitivity
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Description
This quiz covers the production of heme, a crucial molecule in the body, and porphyrias, a group of rare disorders caused by defects in heme synthesis. Learn about the enzyme deficiencies that lead to these conditions.
