Adverse drug reactions to azathioprine (AZA), the pro-drug of 6-mercaptopurine (6-MP), occur in 15% to 28% of patients and the majority are not explained by thiopurine methyltransferase (TPMT) deficiency. Inosine triphosphate pyrophosphatase (ITPase) deficiency results in the benign accumulation of the inosine nucleotide ITP. 6-MP is activated through a 6-thio-IMP intermediate and, in ITPase deficient patients, potentially toxic 6-thio-ITP is predicted to accumulate. The association between polymorphism in the ITPA gene and adverse drug reactions to AZA therapy was studied in patients treated for inflammatory bowel disease. Sixty-two patients with inflammatory bowel disease suffering adverse drug reactions to AZA therapy were genotyped for ITPA 94C>A and IVS2 + 21A>C polymorphisms, and TPMT*3A, *3C, *2 polymorphisms. Genotype frequencies were compared to a consecutive series of 68 controls treated with AZA for a minimum of 3 months without adverse effect. The ITPA 94C>A deficiency-associated allele was significantly associated with adverse drug reactions [odds ratio (OR) 4.2, 95% confidence interval (CI) 1.6-11.5, P = 0.0034]. Significant associations were found for flu-like symptoms (OR 4.7, 95% CI 1.2-18.1, P = 0.0308), rash (OR 10.3, 95% CI 4.7-62.9, P = 0.0213) and pancreatitis (OR 6.2,CI 1.1-32.6, P = 0.0485). Overall, heterozygous TPMT genotypes did not predict adverse drug reactions but were significantly associated with a subgroup of patients experiencing nausea and vomiting as the predominant adverse reaction to AZA therapy (OR 5.5, 95% CI 1.4-21.3, P = 0.0206). Polymorphism in the ITPA gene predicts AZA intolerance. Alternative immunosuppressive drugs, particularly 6-thioguanine, should be considered for AZA-intolerant patients with ITPase deficiency.

Summary Background:  Thioguanine nucleotides (TGNs) are the active product of thiopurine metabolism. Levels have been correlated with effective clinical response. Nonetheless, the value of TGN monitoring in clinical practice is debated. We report the influence of introducing TGN monitoring into a large adult inflammatory bowel disease (IBD) clinic. Patients and methods:  Patients with IBD undergoing TGN monitoring were identified from Purine Research Laboratory records. Whole blood TGNs and methylated mercaptopurine nucleotides were hydrolysed to the base and measured using HPLC. Clinical and laboratory data were obtained retrospectively. Results:  One hundred and eighty‐nine patients with 608 available TGN results were identified. In non‐responders, TGNs directed treatment change in 39/53 patients. When treatment was changed as directed by TGN, 18/20 (90%) improved vs. 7/21 (33%) where the treatment decision was not TGN‐directed, p < 0.001. Where treatment change was directed at optimisation of thiopurine therapy, 14/20 achieved steroid‐free remission at 6 months vs. 3/10 where the TGN was ignored, (p = 0.037). Six per cent of patients were non‐adherent, 25% under‐dosed and 29% over‐dosed by TGN. Twelve per cent of patients predominantly methylated thiopurines, this group had low TGN levels and high risk of hepatotoxicity. In responders, adherence and dosing issues were identified and TGN‐guided dose‐reduction was possible without precipitating relapse. Mean cell volume (MCV), white blood cell count (WBC) and lymphocyte counts were not adequate surrogate markers. MCV/WBC ratio correlated with clinical response, but was less useful than TGN for guiding clinical decisions. Conclusions:  Monitoring TGNs enables thiopurine therapy to be optimised and individualised, guiding effective treatment decisions and improving clinical outcomes.

Pyrimidine 5 nucleotidase (P5N-1) deficiency is an autosomal recessive condition causing hemolytic anemia characterized by marked basophilic stippling and the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. It is implicated in the anemia of lead poisoning and is possibly associated with learning difficulties. Recently, a protein with P5N-1 activity was analyzed and a provisional complementary DNA (cDNA) sequence published. This sequence was used to study 3 families with P5N-1 deficiency. This approach generated a genomic DNA sequence that was used to search GenBank and identify the gene for P5N-1. It is found on chromosome 7, consists of 10 exons with alternative splicing of exon 2, and produces proteins 286 and 297 amino acids long. Three homozygous mutations were identified in this gene in 4 subjects with P5N-1 deficiency: codon 98 GAT3GTT, Asp3Val (linked to a silent polymorphism codon 92, TAC3TAT), codon 177, CAA3TAA, Gln3termination, and IVS9-1, G3T. The latter mutation results in the loss of exon 9 (201 bp) from the cDNA. None of these mutations was found in 100 normal controls. The DNA analysis was complicated by P5N-1 pseudogenes found on chromosomes 4 and 7. This study is the first description of the structure and location of the P5N-1 gene, and 3 mutations have been identified in affected patients from separate kindreds. ( IntroductionPyrimidine 5Ј nucleotidase (P5ЈN-1, also known as uridine-5Ј-monophosphate hydrolase-1) catalyzes the dephosphorylation of the pyrimidine 5Ј monophosphates UMP and CMP to the corresponding nucleosides. A deficiency of this enzymatic activity was first identified by Valentine et al 1,2 in erythrocyte stroma while investigating patients with hemolytic anemia characterized by marked basophilic stippling. Initial studies showed very high concentrations of what were assumed to be adenine nucleotides in the erythrocytes, but these were later found to be pyrimidine nucleotides; the red blood cells (RBCs) also contained high levels of glutathione and reduced activity of ribose-phosphate pyrophosphokinase. Studies on 3 additional kindreds with hemolytic anemia and basophilic stippling demonstrated absent or markedly reduced pyrimidine 5Ј nucleotidase activity in their RBCs. 3 Reports of 40 patients with this condition have been published, with presumably large numbers undetected. However, because of the lack of a simple and reliable test for carriers, the exact prevalence of the condition is unknown. Reported numbers of homozygotes suggest that it is the third most common RBC enzymopathy-after glucose-6-phosphate dehydrogenase and pyruvate kinase deficiency-causing hemolysis. 4 Although the first 6 patients reported were all female, a number of affected males have been reported since then, and the pattern of inheritance is typical of an autosomal recessive disorder. 5 Additional studies have suggested that there are 2 isozymes of P5ЈN in RBCs, one with a preference for UMP and CMP, referred to as P5ЈN-1, and one able to hydrolyze deoxypyrimid...