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Genetics of Acute Intermittent Porphyria

written by: R. Elizabeth C. Kitchen•edited by: lrohner•updated: 12/31/2010

If you need information about the genetics of acute intermittent porphyria read on to get the details about the genetics and about this disorder.

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    Acute intermittent porphyria is classified as a hepatic porphyria. Through understanding the genetics of acute intermittent porphyria, we know that low levels of the enzyme known as porphobilinogen deaminase or hydroxymethylbilane synthase is the cause. Symptoms may be triggered by factors, such as drugs, hormones, and dietary changes. Most patients with this disorder will never develop symptoms. This disorder affects about one to two in 100,000 people.

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    This disorder is caused by an HMBS gene mutation. This gene creates the hydroxymethylbilane synthase enzyme which is very important to the chemical process that results in the production of heme. An acute attack occurs when byproducts of the process build up within the body. This disorder is inherited in an autosomal dominant pattern.

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    Signs and Symptoms

    Most patients with this disorder will never develop symptoms. When symptoms do occur, they usually happen in the forum of an attack that can last from several hours to several days. The most common symptom is abdominal pain and this pain can be quite severe. Other possible signs and symptoms may include:

    • Nausea
    • Constipation
    • Muscle weakness
    • Palpitation
    • Hallucinations
    • Vomiting
    • Pain in the arms, legs, and back
    • Urinary retention
    • Confusion
    • Seizures
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    This disorder is often difficult to diagnose due to the fact that it can mimic many other conditions that are more common and it is rare. To establish that a patient has an acute porphyria, increased levels of porphobilinogen and delta-aminolevulinic acid have to be found in the urine. Diagnosis may also occur as a result of normal red blood cells having deficient PBGD. In some cases, where the right knowledge and family history is present, DNA testing may aid in diagnosis.

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    Acute attacks often require the patient to be hospitalized. During a patient's hospitalization, close observation, and medications for the nausea, vomiting, and pain will be administered. Disease activity may be suppressed by a high intake of carbohydrates, like glucose. These are often given orally or intravenously. For a more potent method in suppressing disease activity, intravenous heme therapy is often effective and can be started once the patient has had a trial of glucose therapy.

    During an attack, certain drugs should be stopped, such as sulfonamides, barbiturates, and many other medications. Dietary counseling is also helpful because patients need to avoid certain foods and consume more of certain others, such as carbohydrates. If diagnosis and proper treatment are begun prior to severe nerve damage, the prognosis is often quite good. Patients with this disorder may develop other diseases.

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    Genetic and Rare Disease Information Center. (2009). Acute Intermittent Porphyria. Retrieved on December 29, 2010 from the National Institutes of Health Office of Rare Disease Research:

    DeLoughery, T.G. MD. (2009). Porphyria, Acute Intermittent. Retrieved on December 29, 2010 from eMedicine: