The Watson-Schwartz test for porphobilinogen is an excellent, simple screening procedure for porphyria and certainly its use should be considered in any patient with a history of abdominal pain, constipation, obscure neurological disorder, mental disturbance, multiple abdominal operations, or dark urine.
The porphyrias are a group of inherited disorders of porphyrin metabolism (Table) manifested chemically by an increased excretion of the porphyrins and their precursors or both.
Porphyrins are normally synthesized from glycine and succinic acid which combine to yield α-amino-β-ketoadiptic acid. Decarboxylation results in δ-aminolevulinic acid. Two molecules of δ-aminolevulinic acid condense, forming the monopyrolle, porphobilinogen. Four molecules of porphobilinogen condense producing the various tetrapyrolle porphyrinogens (copro-, uro-, protoporphyrinogen), the reduced, colorless precursors of the porphyrins.1 Porphyrins linked to metal and protein constitute the important biological compounds: hemoglobin, myoglobin, cytochrome, and catalase.
Varieties of Porphyria.—
Porphyria Erythropoietica. —Inherited as an autosomal recessive, it accounts for only 3% of