Tórsdóttir et al Gamma glutamyl transpeptidase (GGT) is localised predominantly within the cytoplasm of hepatocytes and biliary epithelial cells of the liver. It has been recognized as a useful marker of liver disease.8 As CP in serum is produced in hepatocytes, the determination of GGT activity in serum is of use, as damage of hepatocytes can be a cause for changes in CP parameters. At the time of this study, there were ﬁve living Wilson patients in Iceland. All of the known patients in Iceland have had the same mutation, a 7-bp deletion in exon 7 on chromosome 13, and this mutation is not known elsewhere in the world.9 This study was undertaken in order to elucidate whether the heterozygotes for the unique Icelandic type of WD had any particular derangement of their copper metabolism. Material and methods The ﬁve known Icelandic WD patients and 20 healthy, ﬁrst-degree relatives of the WD patients (heterozygotes) were traced (parents, siblings, and children of the patients). The mean age of the heterozygotes was 41 years (range 21–70), nine males and 11 females. Each heterozygote had healthy age- and gender-matched control. The blood samples were taken in the morning in the fasting state, and the blood sampling units used were specially prepared for metal analysis (Sarstédt®). The same blood sampling procedure was used for the WD patients, heterozygotes and controls. All the WD patients were on copper-chelating treatment. The study was approved by the Icelandic National Bioethics Committee (01-056-S1) and registered by The Data Protection Authority. Determination of gamma glutamyl transpeptidase GGT activity in serum, expressed as units/l, was determined at the Icelandic University Hospital Laboratories, on Vitros 950, Ortho-Clinical Diagnostics, Rochester, NY, USA. GGT catalyzes the transfer of the gamma-glutamyl portion of L-gamma-glutamyl-p-nitroanilide to glycylglycine, simultaneously producing p-nitroaniline. The rate of change in reﬂection density is measured and used to calculate the enzyme activity of GGT. The upper limit of GGT in healthy subjects is 70 units/l at these laboratories. Determination of copper in plasma A solution of 0.5 ml plasma, 5 ml of double distilled water, 0.2 ml of concentrated hydrochloric acid (Emerck, Darmstadt, 56 100318) and 0.125 ml of concentrated nitric acid (E Merck, 100456) was pipetted into a Teﬂon-lined microwave acid digestion bomb. The digestion bomb was heated in a 600 W microwave oven for 3.25 min. After cooling, 10 ml of distilled water were added and samples taken to analysis. A standard serum from Nycomed Pharma AS, Oslo, Norway, was processed in the same way. Copper in the samples (μmol/l plasma) was determined at the Icelandic Fisheries Laboratories, Reykjavík, by atomic absorption spectrophotometry. Determination of CP concentration Ceruloplasmin levels in serum (mg/l) were determined at the Icelandic University Hospital Laboratories with rate nephelometry immunoassay (Beckman Immunochemistry Systems, ICS-2 Beckman Instruments Inc.). The CP antibody was processed goat sera, which were calibrated with an Inter- national Federation of Clinical Chemistry human calibrator. The results are represented as μmol/l in Table 1. Determination of CP oxidative activity in serum Ceruloplasmin oxidative activity in serum (units/ml) was determined at the Department of Pharmacology and Toxicology, University of Iceland, with the manual kinetic assay described by Boyett and colleagues.10 The method is based on the oxidative activity of CP with o-dianisidine as substrate. The substrate reagent was prepared at this laboratory as follows: 250 mg of o-dianisidine were added to 50 ml of distilled water. 1.0 ml Triton X-100 was added and the solution then topped up to 100 ml with distilled water. Just before use 2.0 ml of the o-dianisidine solution was topped up to 10 ml with acetate buffer solution. 0.15 ml of serum was incubated with 3.0 ml of substrate reagent in a cuvette positioned in a spectrophotometer. The change in absorbance at 460 nm with time was observed. The enzyme activity was reported as units/ml, based on the molar absorption coef- ﬁcient of o-dianisidine consumed. Determination of superoxide dismutase (SOD1) activity in erythrocytes Superoxide dismutase activity in erythrocytes (SOD- 525 units) was determined at the Department of Pharmacology and Toxicology, University of Iceland, with a spectropho- tometric assay (Bioxytech®, SOD-525) as described by Nebot and colleagues.11 The superoxide dismutase activity in the erythrocytes of both the patients and their controls was determined the same day. The assay is based on the SOD-mediated increase in the rate of auto-oxidation of Neuropsychiatric Disease and Treatment 2009:5