Acute Intermittent Porphyria

What is acute intermittent porphyria?

Acute intermittent porphyria is probably the most common porphyria with acute (severe but usually not long-lasting) symptoms. The disorder results from low levels of the enzyme responsible for the third step in haeme production. Haeme is a vital molecule for all of the body's organs. It is a component of haemoglobin, the molecule that carries oxygen in the blood.

Acute intermittent porphyria is a subtype of porphyria.

About 80 percent of people with reduced enzyme activity never experience signs or symptoms of acute intermittent porphyria, and others may have only one or a few acute attacks during their lives. When symptoms occur, they are the most severe of any type of porphyria. Acute attacks cause abdominal pain, vomiting, diarrhoea, and constipation. During an attack, a person may also experience muscle weakness, seizures, and mental changes such as anxiety and hallucinations. These symptoms can be life-threatening in rare cases. Attacks are triggered by nongenetic factors such as certain drugs, alcohol, smoking, dieting or fasting, certain hormones, other illnesses, and stress.

In addition to acute attacks, people with acute intermittent porphyria are at an increased risk of developing abnormal liver function and liver cancer.

How common is acute intermittent porphyria?

This disorder occurs in 1 to 2 in 100,000 people in most countries. It is more common in northern European countries, particularly England, Sweden, and Ireland.

What genes are related to acute intermittent porphyria?

Mutations in the HMBS gene cause acute intermittent porphyria.

The HMBS gene makes an enzyme called hydroxymethylbilane synthase, which is critical to the chemical process that leads to haeme production. The activity of this enzyme is reduced by 50 percent in most people with acute intermittent porphyria. Nongenetic factors such as certain drugs, stress, and others listed above can increase the demand for haeme and the enzymes required to make haeme. The combination of this increased demand and reduced activity of hydroxymethylbilane synthase disrupts haeme production and allows byproducts of the process to accumulate in the body, triggering an acute attack.

How do people inherit acute intermittent porphyria?

Acute intermittent porphyria is inherited in an autosomal dominant pattern, which means one copy of the altered gene is sufficient to decrease enzyme activity and cause symptoms.

What other names do people use for acute intermittent porphyria?

* AIP
* Hydroxymethylbilane synthase deficiency
* Intermittent acute porphyria syndrome
* PBGD deficiency
* Porphobilinogen deaminase deficiency
* Porphyria, Swedish type
* Pyrroloporphyria
* Swedish genetic porphyria
* Swedish porphyria
* UPS deficiency
* Uroporphyrinogen synthase deficiency