Thiopurine-methyltransferase (TPMT) and nudix-hydrolase-15 (NUDT15) are enzymes relevant to the metabolism of thiopurine medications, used to treat immunologic disorders and malignancies. Standard dosing administered in the setting of TPMT/NUDT15 dysfunction can cause excessive cytotoxic metabolites and life-threatening complications. We describe an adolescent with high-risk B-cell acute lymphoblastic leukemia (ALL) whose TPMT/NUDT15 status was unknown due to lack of insurance approval for genetic testing. He subsequently developed myelosuppression and severe veno-occlusive disease (VOD) after receiving 6-mercaptopurine (6-MP). Our patient provides an example of a very rare 6-MP-related toxicity and the potential benefit of TPMT/NUDT15 screening before initiating thiopurine therapy.

BACKGROUND: Risk factors for developing pancreatitis due to thiopurines in patients with inflammatory bowel disease (IBD) are not clearly identified. Our aim was to evaluate the predictive pharmacogenetic risk of pancreatitis in IBD patients treated with thiopurines.
METHODS: We conducted an observational pharmacogenetic study of acute pancreatitis events in a cohort study of IBD patients treated with thiopurines from the prospectively maintained ENEIDA registry biobank of GETECCU. Samples were obtained and the CASR, CEL, CFTR, CDLN2, CTRC, SPINK1, CPA1, and PRSS1 genes, selected based on their known association with pancreatitis, were fully sequenced.
RESULTS: Ninety-five cases and 105 controls were enrolled; a total of 57% were women. Median age at pancreatitis diagnosis was 39 years. We identified 81 benign variants (50 in cases and 67 in controls) and a total of 35 distinct rare pathogenic and unknown significance variants (10 in CEL, 21 in CFTR, 1 in CDLN2, and 3 in CPA1). None of the cases or controls carried pancreatitis-predisposing variants within the CASR, CPA1, PRSS1, and SPINK1 genes, nor a pathogenic CFTR mutation. Four different variants of unknown significance were detected in the CDLN and CPA1 genes; one of them was in the CDLN gene in a single patient with pancreatitis and 3 in the CPA1 gene in 5 controls. After the analysis of the variants detected, no significant differences were observed between cases and controls.
CONCLUSIONS: In patients with IBD, genes known to cause pancreatitis seem not to be involved in thiopurine-related pancreatitis onset.

Asparaginases are a mainstay treatment for pediatric acute lymphoblastic leukemia (ALL). Recent reports identified hypoglycemia associated with asparaginases. Other reports describe hypoglycemia associated with 6-mercaptopurine (6-MP), another fundamental ALL therapy. Little is known about the risk of hypoglycemia associated with ALL therapy, an adverse event that puts children at risk of decreased level of consciousness, seizures, and possibly negative neurocognitive sequelae.
We performed a retrospective chart review of 6 children with hypoglycemia during ALL treatment in our institution from May 2016 to August 2019. Timing and duration of hypoglycemia relative to polyethylene glycol (PEG)-asparaginase, 6-MP, and corticosteroids were determined. Laboratory values of the critical sample were collected.
The median age was 2.75 (interquartile range: 1.88 to 3.63) years. Three patients had trisomy 21. The onset of hypoglycemia was 5 to 19 days after the most recent PEG-asparaginase administration or 6 to 7 months after initiating daily 6-MP. Sixteen hypoglycemic events were documented, and 9/16 had a critical sample drawn. Six events were hypoketotic, associated with PEG-asparaginase. Three were ketotic, associated with 6-MP. Two patients required treatment with diazoxide and cornstarch.
Hypoglycemia associated with PEG-asparaginase occurred later and lasted longer than previous reports with l-asparaginase, with the likely mechanism being hyperinsulinism. 6-MP was associated with ketotic hypoglycemia.

BACKGROUND: Mercaptopurine (6MP) and methotrexate (MTX) are commonly used for maintenance chemotherapy for acute lymphoblastic leukemia (ALL). These medications have been associated with various side effects such as myelosuppression, colitis, and thyroiditis in addition to numerous cutaneous adverse events. Cutaneous side-effects most reported include mucositis, alopecia, xerosis, and pruritus. We report an interesting case of hand-foot syndrome to 6MP in a child on maintenance therapy for B-cell ALL from an alteration in medication metabolism.
METHODS: We report a 10-year-old male on maintenance chemotherapy for pre-Bcell ALL who presented to the hospital with worsening oral lesions and erythematous, fissured plaques on the palms and soles. Maintenance therapy consisted of IV vincristine and 5-day pulse of steroids every 12 weeks, daily 6MP, and weekly MTX, which were increased to  ≥ 150% of standard dosing due to persistent absolute neutrophil counts  > 1500. Metabolites obtained on admission demonstrated elevated 6MMP metabolites at 35,761 (normal < 5700). TPMT and NUDT15 enzyme activity were normal and no alterations in genotyping were discovered.
RESULTS: Patient\'s oral chemotherapy, including both 6MP and MTX, were stopped and allopurinol 100 mg daily was initiated, which lead to overall improvement.
CONCLUSIONS: Clinical findings of acute mucositis and worsening of hand-foot syndrome, in the setting of inadequate myelosuppression in a child on maintenance therapy for ALL should raise concerns to consider altered metabolism pathway leading to toxic metabolite buildup. Allopurinol can play in improving cutaneous manifestation and chemotherapeutic dosing in patients with altered metabolism.

OBJECTIVE: Azathioprine, a prodrug of 6-mercaptopurine (6-MP), is used in the treatment of inflammatory bowel disease and may be continued during pregnancy. Acute cholestatic liver injury has been reported to occur with azathioprine. We aimed to examine azathioprine related cholestasis effect on pregnancy complications and outcome.
METHODS: We present a unique case of 6-MP-induced severe intrahepatic cholestasis of pregnancy (ICP) that required meticulous combined therapy including plasma exchange. The symptoms resolved following 6-MP withdrawal. A literature review revealed 11 pregnancies complicated by early-induced severe ICP among women treated with azathioprine or 6-MP.
CONCLUSIONS: We recommend weekly bile acid level tests for pregnant women treated with azathioprine or 6-MP, beginning early in the second trimester of pregnancy, and the prompt discontinuation of treatment upon establishment of an ICP diagnosis.

An 82-year-old man was treated with ipilimumab and nivolumab for malignant pleural mesothelioma. Although he was previously treated with prednisolone (1 mg/kg/day) for immune-related adverse event (irAE) hepatitis by a previous doctor, he still had worsening liver function and was transferred to our hospital. Blood tests and imaging findings were negative for autoimmune and infectious hepatitis, and liver biopsy results were consistent with irAE hepatitis. Steroid pulse therapy improved liver function, but tapering to prednisolone (1 mg/kg/day) again worsened his liver function. Concomitant use of mycophenolate mofetil was initiated, but no improvement in liver function was observed, therefore azathioprine, a thiopurine immunosuppressant, was administered in combination with steroids. During the course of treatment, hepatic dysfunction due to azathioprine was suspected, and the concomitant use of mercaptopurine and prednisolone was started. Afterward, the liver function improved, and the prednisolone dose was gradually reduced to 10 mg/day. This is a rare case in which a thiopurine-based immunosuppressant was effective against irAE hepatitis, therefore thiopurine-based immunosuppressants may be effective against steroid-refractory hepatitis.

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BACKGROUND Systemic IgG4-related disease is a rare disease that can affect the hepatobiliary system and may lead to tissue fibrosis and organ failure. Diagnostic criteria for IgG4-related disease are well established, and systemic glucocorticoids are recommended for initiation of treatment. Besides the beneficial properties of glucocorticoids, the long-term treatment with systemic steroids carries the risk of toxicity, especially in elderly patients, in whom IgG4-related disease is more common. Furthermore, disease relapses may occur during the tapering of steroids. Overall, the optimal treatment approach for maintenance therapy has not been clarified yet and is an area of current clinical research. CASE REPORT We present a patient with IgG4-related sclerosing cholangitis and histologically confirmed systemic (multi-organ) IgG4-related disease who was at increased risk of disease recurrence. The effects of immunosuppressants (prednisolone, 6-mercaptopurine, budesonide) on clinical symptoms, laboratory parameters (AST, ALT, AP, γGT, bilirubin), and imaging examinations (magnetic resonance cholangiography) were documented over 56 months. Control of IgG4-related sclerosing cholangitis was achieved - without systemic prednisolone - with the locally acting glucocorticoid budesonide in combination with low-dose 6-mercaptopurine. During treatment with 6-mercaptopurine, transient hepatotoxicity occurred, which was reversed by intermittent pausing and subsequent dose reduction. In addition, gangrenous cholecystitis occurred as a complication of immunosuppression and was treated by emergency cholecystectomy. CONCLUSIONS Budesonide could be a new treatment modality for IgG4-related sclerosing cholangitis. Systemic manifestations of immunoglobulin G4-related disease can be controlled with low-dose 6-mercaptopurine. Gangrenous cholecystitis may occur as a complication of immunosuppressive treatment.

Thioguanine (TG) has been shown as a safe alternative in adults with inflammatory bowel disease (IBD) who did not tolerate conventional thiopurines [azathioprine (AZA)/mercaptopurine]. However, data in pediatric IBD are scarce. Therefore, we aimed to assess the safety of TG as maintenance therapy.
A retrospective, multicenter cohort study of children with IBD on TG was performed in the Netherlands. TG-related adverse events (AE) were assessed and listed according to the common terminology criteria for AE.
Thirty-six children with IBD (median age 14.5 years) on TG (median dose 15 mg/day) were included in 6 centers. Five AE occurred during follow-up [pancreatitis (grade 3), hepatotoxicity (grade 3) (n = 2), Clostridium difficile infection (grade 2), and abdominal pain (grade 2)]. All patients (n = 8) with a previously AZA-induced pancreatitis did not redevelop pancreatitis on TG.
In pediatric IBD, TG seems a safe alternative in case of AZA-induced pancreatitis. Further research assessing long-term TG-related safety and efficacy is needed.

Macrophage activation syndrome is a life-threatening syndrome of uncontrolled immune activation with variable clinical presentation making early diagnosis difficult. It is often manifested by the development of multi-organ failure due to systemic inflammatory response. Patients with ulcerative colitis (UC) on purine antimetabolites are at high risk for severe myelosuppression due to the mechanism of thiopurine toxicity which potentially contributes to the development of macrophage activation syndrome. We present a case of a 39-year-old woman with a 2-year history of UC previously treated with 6-mercaptopurine (6-MP) and recent COVID-19 infection, who was admitted to our emergency department for C. difficile infection and subsequently developed macrophage activation syndrome. This case report also raises the question of whether abrupt discontinuation of 6-MP may have contributed to the worsening of the patient\'s symptoms of underlying hemophagocytic lymphohistiocytosis (HLH) and her rapid deterioration. Both macrophage activation syndrome and COVID-19 infection can produce a large number of pro-inflammatory cytokines termed \"cytokine storm,\" but a pro-inflammatory cytokine panel breakdown helps to differentiate between the two. Our case report emphasizes the importance of close monitoring of patients on purine antimetabolite therapy who present with signs and symptoms of systemic toxicity.