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Acute Intermittent Porphyria

This information is being sent to you by the Canadian Association for Porphyria because you believe you may have acute intermittent porphyria (AIP). The information here is intended to apply to AIP in general and may include information which does not apply to your specific case. The information given here describes the condition in all its forms and does not apply specifically to you. 

Most people who have inherited the gene for AIP live quite normal lives and may never be aware of this. Perhaps 10-20% run into some kind of trouble, but this number in uncertain. Unless there is a family history of AIP, they may never be aware of the gene and it will not be diagnosed. 

How does the disease present?
There may be a family history and this must be a blood relative. Abdominal pain, nausea, vomiting and loss of appetite are the most frequent symptoms and are often accompanied by constipation and a fast pulse rate. The urine may be dark or it may darken on standing, particularly in sunlight. The abdominal pain is difficult to describe and does not fit close by descriptions for other diseases. It is important to avoid any unnecessary surgery in an attempt to diagnose the cause of the pain. 

Most patients with AIP never experience anything more severe than the symptoms listed above: let's call this "Stage 1". Beyond stage 1 the events to be described are quite rare.

Stage 2
There will be a change in the level of consciousness and various abnormalities of mental function. Problems may arise with salts and water in the body (technically called "hyponatremia"). The abdominal pain, vomiting, etc. may become worse.

Stage 3
Muscle weakness may develop. Nerves supplying both muscles and sensation do not conduct properly and the disturbances of brain function listed under stage 2 become more severe. Finally, the muscles that govern breathing may become paralyzed and under these circumstances, death is possible unless the patient is supported in a hospital. 

Stage 4
This is the stage of recovery. Recovery from stages 1 and 2 (above) will be complete. However, if the peripheral nerves have been affected, i.e. if muscle weakness has developed during the acute attack of AIP, some residual paralysis may remain and this may take from one-half to three years for recovery to be complete. In the occasional patient it may never be complete. 

It cannot be overstressed that the events described in stages 2, 3, and 4 are uncommon today and your chance is small of suffering such severe illness once you know you have AIP, are properly treated, and take reasonable precautions.

What causes an acute attack in AIP?
Part of the answer is "we don't know", but there are important things we do know. One of these is that acute porphyria seems to have become a problem after the introduction of manmade organic chemicals as drugs in the late 19th century. Second, some drugs (barbiturates, sulfonamides, anti-epileptic drugs, and a few others) will definitely precipitate acute porphyria in a person who carries the gene for AIP. Some women have clearly experienced acute attacks, usually of the "stage 1" severity at the time of their menstrual periods or in the middle of the menstrual cycle. There is evidence in some women of a relationship to hormone changes in the body, but exactly what changes precipitate the condition is not clear. 

There is some evidence that starvation is particularly bad for patients with AIP and you should avoid going without food for more than 12 hours if possible, particularly, you should avoid diets which involve stringent reductions in food intake or fasting. Alcohol appears to be harmful to some patients with AIP and it would be prudent to abstain from alcohol. There is reason to believe that cigarette smoking may be deleterious and there are, of course, many reasons for avoiding cigarettes. There are one or two accounts of acute porphyria being precipitated by exposure to sunlight; the reason for this is not understood, but sunbathing is a stress on the body which changes the secretion of some hormones, and again it would be wise to avoid this risk.

It is much easier to indicate which drugs are definitely bad than to say which drugs are definitely safe, in fact, this is almost impossible to do. We live in a society which tends to accept the idea of "a pill for every ill" but if you have the gene for AIP, you should avoid taking any drugs whether purchased in the pharmacy, over the counter, or given to you by your doctor, unless you have a serious condition which requires to be treated. Do not take any drugs for trivial complaints. 

How is AIP diagnosed?
Let's deal with the acute attack first, because this is the most important situation where the diagnosis must be right and must be made fast. If you have acute porphyria, your urine will always contain increased amounts of aminolevulinic acid and porphobilinogen called the "watson-Schwartz" test. If it is suspected that you have abdominal pain or some other symptom due to acute porphyria, this test must be positive. If porphobilinogen cannot be measured in the hospital where you are, either the test must be run immediately somewhere else, or you should be transferred to a different hospital. If the porphobilinogen test is negative, some other cause for the symptoms must be sought. Further, the severity of the acute attack can be followed by observing daily porphobilinogen levels in urine.

How is AIP diagnosed at other times?
This is not so simple. A 24 hour urine collection can be tested for aminolevulinic acid and porphobilinogen, but if normal levels are obtained, this does not exclude the possibility that you carry the gene for the condition. However, a positive test makes it likely that you do carry the gene for AIP, provided a test of your stool for porphyrins is not abnormal. 

A second test can be performed on your blood. This tests for something called "porphobilinogen deaminase" (also called "uroporphyrinogen synthase") and about 90% of patients with the gene for AIP show a reduced level of this. This is called an enzyme test and is only available in a few specialized laboratories. The Porphyria Foundation of Canada will tell you where the test can be done. You must realize that the level of false positives (a low value in a person who is actually normal) and false negatives (a normal value in a person who is actually affected) is rather high and by itself the test is imperfect. However, it is the only test available to test children before puberty.

Will my children be affected?
Whether you are male or female, any child of yours has a 50% chance of inheriting the gene which determines AIP - see the diagram of dominant inheritance. Presently, this cannot be recognized until a baby is old enough for a blood sample to be taken for the enzyme test mentioned above. The unsatisfactory nature of this test has been described. However, acute attacks (the only symptoms we need be concerned about) do not occur prior to puberty.

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