1 6-Mercaptopurine is extensively used in the treatment of childhood lymphoblastic leukaemia to prolong the duration of remission achieved with other drugs. The response to remission maintenance therapy varies widely. 2 We investigated the relationship between red blood cell 6-thioguanine nucleotide, a metabolite of 6-mercaptopurine, and myelosuppression in 22 children with acute lymphoblastic leukaemia in remission. The peripheral neutrophil count was used as an index of myelosuppression. 3 6-Mercaptopurine dose was related to 6-thioguanine nucleotide concentration (r = 0.4; P < 0.001; n = 90; y = 18.51 + 0.36 x). Large individual variations around the regression line are observed. 4 Neither 6-mercaptopurine dose nor 6-thioguanine nucleotide concentration was related to the neutrophil count at the time of sampling (day 0) or 7 days later. 5 Both 6-mercaptopurine dose and 6-thioguanine nucleotide concentration correlated with the neutrophil count at day 14 (r = -0.33; P < 0.01; n = 90 and r = -0.3; P < 0.01; n = 90 respectively). This delay is compatible with a cytotoxic action on bone marrow stem cells. 6 Excluding children with other, uncontrolled, potentially myelosuppressive influences the correlation between 6-thioguanine nucleotide concentration and neutropenia improved (r = -0.6; P < 0.001; n = 37). A significant degree of neutropenia was observed by day 14 if the 6-thioguanine nucleotide concentration (day 0) was > 210 pmol/8 x 108 RBCs. 7 The assay of 6-thioguanine nucleotide may highlight those individuals with pharmacokinetic resistance. Two children on continuous high dose 6-mercaptopurine, had low red blood cell 6-thioguanine nucleotide concentrations and neutropenia was not observed.

An assay for 6-thioguanine (6-TG) nucleotide, a major metabolite of the cytotoxic drugs azathioprine, 6-mercaptopurine and 6-thioguanine in human red blood cells (RBCs) has been developed. The metabolite was not detected in RBCs when azathioprine or 6-mercaptopurine was incubated with whole blood in-vitro. The assay for intracellular 6-TG nucleotide is specific and requires 8 X 10(8) RBCs (100 microliters packed cells) for which the limit of sensitivity is 30 pmole 6-TG nucleotide. Pre-dose blood samples were obtained, 12 h after the last azathioprine dose, from 10 renal transplant recipients with stable functioning cadaver grafts on a total daily dose of 150 mg azathioprine. The mean 6-TG nucleotide concentration was 171 pmole/8 X 10(8) RBCs (s.d. = 84). The assay is also suitable for use in measuring 6-TG nucleotide in the RBCs of leukaemic children undergoing 6-mercaptopurine treatment.

SUMMARY A 23 year old woman presented with facial pain, a right parotid tumour and iron deficiency anaemia. She had several cutaneous venous swellings and tumours with a similar appearance were found in the large bowel. Histological examination of the parotid tumour and angiography of the skin and gut lesions confirmed that they were venous in origin. The aetiology, classification, and complications of disorders of the venous system and the importance of using a tourniquet to examine the peripheral veins is discussed.There is an ill defined group of conditions characterised by the coexistence of lesions in both the skin and the internal organs. For example, in blue rubber bleb naevus disease haemangiomas in the skin are associated with vascular polyps in the bowel. The latter may give rise to occult or frank gastrointestinal tract bleeding resulting in anaemia.We have recently investigated a woman who presented with anaemia and a unilateral parotid swelling. She also had unusual skin lesions which seemed to arise from veins, and we found vascular tumours with similar appearances in the large bowel. This combination of abnormalities led to the diagnosis of blue rubber bleb naevus disease. Angiography confirmed that the skin and the bowel lesions were part of the venous system. This case illustrates firstly that careful examination of the skin of patients with anaemia may reveal the cause, and secondly how detailed investigation of vascular lesions helps in classification.Case history A 23 year old shop assistant initially visited her general practitioner because of heavy menstrual bleeding. He thought she was anaemic and prescribed oral iron supplements. Three years later, in

6-Mercaptopurine is extensively used in the treatment of childhood lymphoblastic leukaemia to prolong the duration of remission achieved with other drugs. The response to remission maintenance therapy varies widely. 2 We investigated the relationship between red blood cell 6-thioguanine nucleotide, a metabolite of 6-mercaptopurine, and myelosuppression in 22 children with acute lymphoblastic leukaemia in remission. The peripheral neutrophil count was used as an index of myelosuppression. 3 6-Mercaptopurine dose was related to 6-thioguanine nucleotide concentration (r = 0.4; P < 0.001; n = 90; y = 18.51 + 0.36 x). Large individual variations around the regression line are observed. 4 Neither 6-mercaptopurine dose nor 6-thioguanine nucleotide concentration was related to the neutrophil count at the time of sampling (day 0) or 7 days later. 5 Both 6-mercaptopurine dose and 6-thioguanine nucleotide concentration correlated with the neutrophil count at day 14 (r =-0.33; P < 0.01; n = 90 and r =-0.3; P < 0.01; n = 90 respectively). This delay is compatible with a cytotoxic action on bone marrow stem cells. 6 Excluding children with other, uncontrolled, potentially myelosuppressive influences the correlation between 6-thioguanine nucleotide concentration and neutropenia improved (r =-0.6; P < 0.001; n = 37). A significant degree of neutropenia was observed by day 14 if the 6-thioguanine nucleotide concentration (day 0) was > 210 pmol/8 x 108 RBCs. 7 The assay of 6-thioguanine nucleotide may highlight those individuals with pharmacokinetic resistance. Two children on continuous high dose 6-mercaptopurine, had low red blood cell 6-thioguanine nucleotide concentrations and neutropenia was not observed.

Of 108 renal transplant recipients (53 men and 55 women) treated with azathioprine (0.8-2.9 mg/kg/day) and prednisolone (10 mg daily), 10 men had actinic keratoses, and five of these had squamous cell carcinoma, on light-exposed areas of skin. The time from transplantation to diagnosis of these skin lesions varied from 1.2 to 9.0 (mean 5.1) years. The concentration of the active azathioprine metabolite 6-thioguanine nucleotide was 120-425 (mean 276) pmol per 8 X 10(8) red blood cells in the transplant patients who developed skin lesions and 54-203 (mean 130) pmol per 8 X 10(8) red blood cells in a matched control group of renal transplant recipients. This difference was statistically significant (P = 0.005). There was no statistically significant difference between patients and controls in azathioprine dosage, clinical features of immunosuppression, sunlight exposure or infection with human papilloma virus. The association of raised 6-thioguanine nucleotide concentrations in red blood cells with actinic keratoses and malignant skin tumours in these patients supports chemical carcinogenesis as a possible cause.