We report the case of an 1l-y-old boy with a plasma Zn concentration greater than 200 micromol/L, but with symptoms consistent with Zn deficiency. He has had hepatosplenomegaly, rashes, stunted growth (<3rd centile), anemia, and impaired immune function since infancy. He also has vasculitis and osteoporosis. A plasma Zn-binding protein has been separated and characterized by a combination of size exclusion and ion exchange chromatography and electrophoretic studies and by immunologic methods. Antibodies to the partially purified protein have been raised in rabbits. Size exclusion chromatography shows that Zn is bound to a protein with a mass 110000-300000 kD. Electrophoretic and mass spectrometry studies suggest that the protein may be composed of several subunits. One component of the isolated protein reacts with antiserum to alpha2-macroglobulin; immunoprecipitation studies confirm that the protein is not alpha2-macroglobulin or a histidine-rich glycoprotein. Kinetic studies of zinc metabolism in the patient and his mother with stable Zn isotopes show the presence of increased exchangeable Zn, with a rapid flux from plasma to a stable pool. Liver and muscle Zn and Cu concentrations are raised, but with no abnormal liver histology. Immunoreactive metallothionein in the liver is increased. We suggest that this boy may suffer from a previously unrecognized inborn error of Zn metabolism causing symptomatic zinc deficiency.

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Objective: This study was designed to test whether fractional absorption calculated from urinary enrichment of stable isotopes of zinc accurately re¯ects true absorption measured by faecal monitoring. Design: The two techniques were directly compared in volunteers, whereby each subject acted as his/her own control. Setting: Volunteers were healthy adults, living at home, who were taking part in a larger study on zinc. They attended the local hospital for isotope administration. Subjects: Fifteen volunteers were recruited, seven of whom had non-insulin dependent diabetes mellitus. All completed the study, but ®ve did not carry out a complete faecal collection. Interventions: Each subject received an oral and i.v. dose of different stable isotopes of zinc with breakfast. Faecal and urinary enrichment with the isotopes was measured. Results: There was no signi®cant correlation between the two measures of absorption. Conclusions: The double label stable isotope technique for determining zinc absorption from measurements of urinary enrichment does not reliably predict true zinc absorption (measured by faecal and urinary monitoring) in a heterogenous group of adults given relatively low doses of stable isotopes of zinc. Sponsorship: This work was funded by the European Commission (Training and Mobility Programme).

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