A MOLECULAR VIEW OF THE NEUROLOGIC PORPHYRIAS

The neurologic porphyrias are a group of four clinically related disor ders, each caused by deficiency of a different enzyme of heme synthesi s. Conventional biochemical testing for these disorders is based on th e analysis of porphyrins and their precursors in urine and feces. The complementary DNA sequence and gene organization of all four enzymes h ave now been determined, and this information has laid the foundation for molecular testing. More than 60 mutations causing acute intermitte nt porphyria have been reported, and mutations causing hereditary copr oporphyria, variegate porphyria and ALA dehydratase deficiency have be en described as well. Ln families with a known mutation, DNA-based tes ting offers greater accuracy than traditional biochemical tests in ide ntifying or excluding gene carriers.