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In humans, porphyrins are the main precursors of heme, an essential constituent of hemoglobin, myoglobin and cytochrome.
Deficiency in the enzymes of the porphyrin pathway leads to insufficient production of heme. This is, however, not the main problem; most enzymes - even when less functional - have enough residual activity to assist in heme biosynthesis. The largest problem in these deficiencies is the accumulation of porphyrins, the heme precursors, which are toxic to tissue in high concentrations. The chemical properties of these intermediates determine in which tissue they accumulate, whether they are photosensitive , and how the compound is excreted (in the urine or feces).
There are eight enzymes in the heme biosynthetic pathway: the first and the last three are in the mitochondria, while the other four are in the cytosol.
The hepatic porphyrias include:
The erythropoetic porphyrias include:
Variegate porphyria (also porphyria variegata or mixed porphyria) results from a partial deficiency in PROTO oxidase , manifests itself with skin lesions similar to those of porphyria cutanea tarda combined with acute neurologic attacks. It may first occur in the second decade of life; there is a cohort of sufferers living in South Africa descended from a single ancestor from the Netherlands, Berrit Janisz, who emigrated in the 17th century.
The hepatic porphyrias primarily affect the nervous system, resulting in abdominal pain, neuropathy, seizureThis article is about the medical condition. In law, seizure can also refer to taking possession of an item: see search and seizure. Seizures (or convulsions are temporary alterations in brain functions due to abnormal electrical activity of a group of brs, and mental disturbances, including hallucinationA hallucination is a false sensory perception in the absence of an external stimulus, as distinct from an illusion, which is a misperception of an external stimulus. Hallucinations may occur in any sensory modality visual, auditory, olfactory, gustatory,s, depressionIt is common to feel sad, discouraged, or "down" once in a while, and anyone in this state might say they are suffering from depression. But for some people, this mood persists. For depression, or any other condition, to be termed "clinical" it must reach, anxietyAnxiety is a complex combination of the feeling of fear, apprehension and worry often accompanied by physical sensations such as palpitations, chest pain and/or shortness of breath. It may exist as a primary disorder or may be associated with other medica, and paranoiaParanoid redirects here. For the Black Sabbath album Paranoid see Paranoid (album). For the role playing game, see Paranoia (RPG). In popular culture, the term paranoia is usually used to describe excessive concern about one's own well-being, sometimes su.
The erythropoeitic porphyrias primarily affect the skinThis article is about skin in the biological sense. For other uses of skin see skin (computing) and skinhead. Regarding exposure of the skin to be seen by others, or prevention of this, see nudity, nudism, modesty, clothing. Fruits such as oranges also ha, causing photosensitivity , blisters, itching, and swelling.
In some forms of porphyria, accumulated heme precursors excreted in the urine may change its color to a reddish or purple hue.
Attacks of the disease can be triggered by drugs ( barbiturates, tranquilizers, oral contraceptives, sedatives), chemicals, certain foods, and exposure to the sun.
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