Laboratory diagnosis of the porphyrias

Article Abstract:

The porphyrias are a group of metabolic diseases in which there is an increased production of porphyrins, porphyrin precursors, or both. (Porphyrins are a class of nitrogen-containing compounds in protoplasm, including heme, the active portion of the hemoglobin molecule.) In the May 16, 1991 issue of The New England Journal of Medicine, researchers show that one particular porphyria, variegate porphyria, may be easier to diagnose on the basis of a sample of bile rather than of urine or feces. The research report also illustrates, however, the great complexities facing the physician trying to diagnose the type of porphyria. The diagnosis is difficult without knowledge of the many steps involved in the synthesis of heme within the body. The clinical symptoms may be loosely classed into two categories, however. Skin symptoms result from the accumulation of porphyrins in the skin. Porphyrins have unusual light-sensitive properties, and skin exposed to the sun is most likely to be affected as the porphyrin molecules absorb ultraviolet rays from the sunlight. Porphyrias may also produce neurological symptoms, but the cause of the symptoms is not well understood. The two most common forms of porphyria in North America are porphyria cutanea tarda, which produces only skin symptoms, and acute intermittent porphyria, which produces only neurological symptoms. The skin symptoms of porphyria cutanea tarda are blister-like lesions and excessive fragility of the skin. This condition results from reduced amounts of a particular enzyme. When the enzyme that converts uroporphyrinogen to coproporphyrinogen is inadequate, the uroporphyrinogen accumulates in the body. Similarly, acute intermittent porphyria results from a different enzyme defect. During the synthesis of heme, four molecules of porphobilinogen must be assembled into a single chain. Porphobilinogen accumulates if this step is defective. Curiously, the accumulation is only intermittent, and many people carrying the disease gene do not have any symptoms of disease at all. Other forms of porphyria include erythropoietic protoporphyria and congenital erythropoietic porphyria. The latter is also referred to as Gaucher's disease and is very rare. (Consumer Summary produced by Reliance Medical Information, Inc.)

Physiological aspects, Metabolism, Inborn errors of, Inborn errors of metabolism, editorial, Porphyria

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Brain death -- well settled yet still unresolved

Article Abstract:

The problems inherent in diagnosing death are reviewed. Death is typically defined not only as the cessation of heart beat and breathing but as the cessation of brain activity. However, the term brain death can be confusing to family members whose loved one is being kept alive on life support systems.

Editorial, Analysis

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The diagnosis of brain death

Article Abstract:

The clinical criteria for diagnosing brain death are reviewed. Topics include the clinical examination, neurologic states that can mimic death, and the confirmatory tests for identifying brain death.

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