Studies on coproporphyrin isomers in urine and feces in the porphyrias

Abstract

The urinary and fecal distribution and the relative proportions of the four coproporphyrin (copro) isomers I–IV were analysed in 20 healthy subjects and in patients suffering from one of the seven common types of hepatic or erythropoietic hereditary porphyrias. The ratios of copro isomers I–IV were analyzed by ion-pair high-performance liquid chromatography (HPLC). Observations showed significantly increased proportions of fecal copro isomer I and decreased proportions of copro isomers III, II and IV in erythropoietic porphyrias. In acute hepatic porphyrias the excretion of fecal copro isomer III is dominant (isomer III=58.4±24.0%; x ̄ ±S.D.) and significantly higher ( P<0.001) than in erythropoietic porphyrias (isomer III=15.3±7.7%; x ̄ ±S.D.) and chronic hepatic porphyrias (isomer III=25.8±7.6%; x ̄ ±S.D.). The increased proportions of fecal copro isomer III proved to be important for the diagnosis of hereditary coproporphyria and porphyria variegata independent of the clinical phase existing. These last two acute hepatic porphyrias also showed markedly elevated percentages of the fecal atypical isomers II and IV. In urine significantly decreased proportions of copro isomer I in acute hepatic porphyrias (isomer I=12.3±6.0%; x ̄ ±S.D.) could be observed as compared with non-acute porphyrias (isomer I=53.7±15.2%; x ̄ ±S.D.). Conversely, the proportion of urinary copro isomer III was significantly higher in acute hepatic porphyrias (isomer III=81.4±6.4%; x ̄ ±S.D.). As expected, the greatest amounts of urinary copro isomer I were found in congenital erythropoietic porphyria (isomer I=92.0±3.3; x ̄ ±S.D.) and protoporphyria with hepatobiliary complications (isomer I=81.3±10.7; x ̄ ±S.D.). The atypical urinary copro isomers II and IV were detected in all types of porphyrias ranging from 0.1 to 11.5%. The combined amounts of copro isomers II and IV show a significantly decreased percentage in congenital erythropoietic porphyria as compared with all other types of hereditary porphyrias. In conclusion, we demonstrate that the characteristic pattern of the copro isomer constellations I–IV in the various types of porphyrias are of differential diagnostic importance. The inversion of the I to III ratio in feces in hereditary coproporphyria and porphyria variegata allows the recognition of gene carriers.