About acute porphyrias

The acute porphyrias are a family of rare, serious, inherited disorders, caused by genetic mutations that affect the body’s process for making heme. There are different types of porphyrias. The acute hepatic porphyrias (AHPs) mainly affect the nervous system while the cutaneous porphyrias mainly affect the skin. Some types of porphyria have both nervous system symptoms and skin symptoms.

Heme is important for your body to deliver oxygen throughout your body

Artboard 1 Liver


  • Acute intermittent porphyria (AIP)
  • Hereditary coproporphyria (HCP)
  • Variegate porphyria (VP)
  • ALAD-deficient porphyria (ADP)

Acute hepatic porphyrias affect 1 of the 8 steps required for the production of heme in the liver. Because the investigational medication being studied works in the liver, only people who have AHP can participate in ENVISION.

The heme pathway

There are several proteins in the liver involved in the pathway that produces heme, including ALA and PBG. This pathway is a multi-step process that is controlled by a protein called ALAS-1. Levels of ALA and/or PBG are elevated in people with AHPs and are thought to cause many of the symptoms.

Triggers such as certain medications, stress, alcohol, hormonal changes, and diet may cause ALAS-1 to increase, causing ALA and PBG to build up in the heme pathway, resulting in an attack.

It is thought that if the production of ALAS-1, the first step in the heme pathway, can be reduced, then the production of the ALA and PBG can be slowed down. This might improve the function of the heme pathway and reduce the potential for these proteins to build up and cause attacks and symptoms.

The investigational medication in ENVISION is called givosiran (giv-ō-sa-ran). It is being studied to see if it can reduce the production of the ALAS-1 protein in the liver.

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