Types of porphyria
For the most part, the various syndromes that are classified under the collective name of porphyria are differentiated from each other on the basis of a combination of clinical symptoms and abnormal biochemical findings in blood, urine, and stool. On the basis of our current understanding of molecular biology this classification is somewhat unsatisfactory and illogical.
One of the earliest classifications was based on whether the major activity of the defective enzyme system is associated with the liver (hepatic) or with the bone marrow (erythropoietic). Often however the same defective metabolic process takes place in both organs. The porphyrias can also be classified by identifying the specific tissues in which the abnormal porphyrin concentrations exert their major toxic effects such as in the skin where they are called cutaneous porphyrias or in the liver where they are called hepatic porphyrias. Other organs such as the nervous system are frequently affected. Frequently, the disease is classified as latent because the patient is asymptomatic until some other outside stimulus such as drugs or sunlight initiates the onset of symptoms in a person who has the genetic predisposition for this disease. In these cases the patient may not even be aware that they are suffering from porphyria until something happens to change the activity of the enzyme system and precipitate the symptoms of the disease.
The most useful and perhaps most popular classification system is grouping certain types of porphyria as acute, occurring suddenly onset of serious potentially life threatening symptoms, or as chronic with intermittent problems that develop gradually over months and persist for years.
Source: This information originally appeared in a booklet written for the Canadian Porphyria Foundation: A Guide to Porphyria (1991) by Dr. Barry A. Tobe, MD, Ph.D, FRCP(C), Toronto, Ontario, Canada. The content has been updated by Dr. Brian M. Gilfix, MDCM, PhD, FRCPC, DABCC, FACB on 22/03/2015.
Last Updated: 22/March/2015