Dubin Johnson syndrome. Abnormal excretion of the isomers of urinary coproporphyrin by clinically unaffected family members

Among clinically unaffected parents and children of Dubin Johnson syndrome (DJS) patients (i.e. obligatory heterozygotes and possibly some homozygotes without clinical expression) statistical proof can be found for an abnormal distribution of urinary, coproporphyrin isomers: the proportion of isomer I being intermediate between that observed in normal controls and that in clinically affected DJS patients. In the intermediate group, however, isomer I excretion is not uniform and the results show a wide range of values, from normal to those obtained for typical DJS patients. This overlapping of values cannot be avoided even by averaging results obtained from several urine samples of the same individual or by examination of 24 hr urine collections. Thus, it is not possible to use the pattern pf urinary coproporphyrin distribution as an exact tool for identification of the genotypes of family members without clinical signs of DJS. However, these results do provide statistical evidence that the genetic defect has a biochemical expression in the heterozygotes or clinically unexpressed homozygous states.