Coproporphyrin excretion in amniotic fluid and urine from premature infants: A possible maturation defect

Coproporphyrin analysis was performed on urine from 17 male and 7 female premature infants (birth wt 1.5-4.5 kg, average 1.7 kg). Six specimens of amniotic fluid obtained before elective abortion induced by saline solution infusion were also examined. Normal adult control subjects excreted 24.6% ± 5.6% of total coproporphyrin as coproporphyrin I. Twenty-three premature infants excreted 59.4% ± 17.3% as coproporphyrin I, significantly higher amounts than control subjects (P < 0.001). Coproporphyrin I excretion in six specimens of amniotic fluid was 84.9% ± 10.4%, significantly higher than in urine from adults and premature infants (P < 0.001). These results raise the possibility of a similar hepatic excretory defect in porphyrin metabolism in the developing fetus and in the Dubin-Johnson syndrome. In the former, the defect is developmental; in the latter, it is lifelong and is present in obligate heterozygotes. Uroporphyrinogen III cosynthetase normally catalyzes conversion of porphobilinogen to isomer III rather than isomer I porphyrins. Developmental deficiency of this enzyme may be responsible for the observed pattern of coproporphyrin isomers seen in the fetus and neonate.