Abnormal Sulfobromophthalein Metabolism in Rotor's Syndrome and Obligate Heterozygotes

Rotor's syndrome is an inheritable disorder characterized by chronic nonhemolytic, predominantly conjugated hyperbilirubinemia without abnormal hepatic pigmentation.^{1 2 3 4} Because of clinical similarities, Rotor's syndrome has been considered to be a variant of the Dubin-Johnson syndrome.^2,3,5 Recent studies of urinary coproporphyrin excretion, however, demonstrate that the two syndromes are distinct pathophysiologic entities.⁶ Studies of hepatic transport of sulfobromophthalein in patients with the Dubin-Johnson syndrome reveal a rise in plasma sulfobromophthalein concentration 90 to 120 minutes after intravenous injection of 5 mg of dye per kilogram.^{7 8 9 10} Moreover, hepatic transport maximum (T_m) is virtually zero, with a normal relative storage capacity (S),.