Tacrolimus is a substrate for P-glycoprotein (P-gp) and cytochrome (CYP) P4503A. P-gp is encoded by the multiple drug resistance gene MDR1 and CYP3A is the major enzyme responsible for tacrolimus metabolism. Both MDR1 and CYP3A5 genes have multiple single nucleotide polymorphisms. The objective of this study was to evaluate whether the MDR1 exon21 and exon26 polymorphisms and the CYP3A5 polymorphism are associated with tacrolimus disposition in pediatric heart transplant patients. At 3, 6 and 12 months post transplantation, a significant difference in tacrolimus blood level per dose/kg/day was found between the CYP3A5 *1/*3 (CYP3A5 expressor) vs. *3/*3 (nonexpressor) genotypes with the *1/*3 patients requiring a larger tacrolimus dose to maintain the same blood concentration. There were no significant differences in tacrolimus blood level per dose/kg/day between MDR1 exon21 G2677T and exon 26 C3435T at 3 months, but both were found to have a significant association with tacrolimus blood level per dose/kg/day at 6 and 12 months. We conclude that specific genotypes of MDR1 and CYP3A5 in pediatric heart transplant patients require larger tacrolimus doses to maintain their tacrolimus blood concentration, and that this information could be used prospectively to manage patient's immunosuppressive therapy.

SummaryBackgroundKCNJ11 mutations cause permanent neonatal diabetes through pancreatic ATP-sensitive potassium channel activation. 90% of patients successfully transfer from insulin to oral sulfonylureas with excellent initial glycaemic control; however, whether this control is maintained in the long term is unclear. Sulfonylurea failure is seen in about 44% of people with type 2 diabetes after 5 years of treatment. Therefore, we did a 10-year multicentre follow-up study of a large international cohort of patients with KCNJ11 permanent neonatal diabetes to address the key questions relating to long-term efficacy and safety of sulfonylureas in these patients.MethodsIn this multicentre, international cohort study, all patients diagnosed with KCNJ11 permanent neonatal diabetes at five laboratories in Exeter (UK), Rome (Italy), Bergen (Norway), Paris (France), and Krakow (Poland), who transferred from insulin to oral sulfonylureas before Nov 30, 2006, were eligible for inclusion. Clinicians collected clinical characteristics and annual data relating to glycaemic control, sulfonylurea dose, severe hypoglycaemia, side-effects, diabetes complications, and growth. The main outcomes of interest were sulfonylurea failure, defined as permanent reintroduction of daily insulin, and metabolic control, specifically HbA1c and sulfonylurea dose. Neurological features associated with KCNJ11 permanent neonatal diabetes were also assessed. This study is registered with ClinicalTrials.gov, number NCT02624817.Findings90 patients were identified as being eligible for inclusion and 81 were enrolled in the study and provided long-term (>5·5 years cut-off) outcome data. Median follow-up duration for the whole cohort was 10·2 years (IQR 9·3–10·8). At most recent follow-up (between Dec 1, 2012, and Oct 4, 2016), 75 (93%) of 81 participants remained on sulfonylurea therapy alone. Excellent glycaemic control was maintained for patients for whom we had paired data on HbA1c and sulfonylurea at all time points (ie, pre-transfer [for HbA1c], year 1, and most recent follow-up; n=64)—median HbA1c was 8·1% (IQR 7·2–9·2; 65·0 mmol/mol [55·2–77·1]) before transfer to sulfonylureas, 5·9% (5·4–6·5; 41·0 mmol/mol [35·5–47·5]; p<0·0001 vs pre-transfer) at 1 year, and 6·4% (5·9–7·3; 46·4 mmol/mol [41·0–56·3]; p<0·0001 vs year 1) at most recent follow-up (median 10·3 years [IQR 9·2–10·9]). In the same patients, median sulfonylurea dose at 1 year was 0·30 mg/kg per day (0·14–0·53) and at most recent follow-up visit was 0·23 mg/kg per day (0·12–0·41; p=0·03). No reports of severe hypoglycaemia were recorded in 809 patient-years of follow-up for the whole cohort (n=81). 11 (14%) patients reported mild, transient side-effects, but did not need to stop sulfonylurea therapy. Seven (9%) patients had microvascular complications; these patients had been taking insulin longer than those without complications (median age at transfer to sulfonylureas 20·5 years [IQR 10·5–24·0] vs 4·1 years [1·3–10·2]; p=0·0005). Initial improvement was noted following transfer to sulfo...

The most common genetic cause of neonatal diabetes and hyperinsulinism is pathogenic variants in ABCC8 and KCNJ11. These genes encode the subunits of the β-cell ATP-sensitive potassium channel, a key component of the glucose-stimulated insulin secretion pathway. Mutations in the two genes cause dysregulated insulin secretion; inactivating mutations cause an oversecretion of insulin, leading to congenital hyperinsulinism, whereas activating mutations cause the opposing phenotype, diabetes. This review focuses on variants identified in ABCC8 and KCNJ11, the ---This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Aims/hypothesis The ABCC8 gene encodes the sulfonylurea receptor 1 (SUR1) subunit of the pancreatic beta cell ATP-sensitive potassium (K ATP ) channel. Inactivating mutations cause congenital hyperinsulinism (CHI) and activating mutations cause transient neonatal diabetes (TNDM) or permanent neonatal diabetes (PNDM) that can usually be treated with sulfonylureas. Sulfonylurea sensitivity is also a feature of HNF1A and HNF4A MODY, but patients referred for genetic testing with clinical features of these types of diabetes do not always have mutations in the HNF1A/4A genes. Our aim was to establish whether mutations in the ABCC8 gene cause MODY that is responsive to sulfonylurea therapy. Methods We sequenced the ABCC8 gene in 85 patients with a BMI <30 kg/m 2 , no family history of neonatal diabetes and who were deemed sensitive to sulfonylureas by the referring clinician or were sulfonylurea-treated. All had tested negative for mutations in the HNF1A and HNF4A genes. Results ABCC8 mutations were found in seven of the 85 (8%) probands. Four patients were heterozygous for previously reported mutations and four novel mutations, E100K, G214R, Q485R and N1245D, were identified. Only four probands fulfilled MODY criteria, with two diagnosed after 25 years and one patient, who had no family history of diabetes, as a result of a proven de novo mutation. Conclusions/interpretation ABCC8 mutations can cause MODY in patients whose clinical features are similar to those with HNF1A/4A MODY. Therefore, sequencing of ABCC8 in addition to the known MODY genes should be considered if such features are present, to facilitate optimal clinical management of these patients.

Introduction: C-peptide measurement in blood or 24-h urine samples provides useful information regarding endogenous insulin secretion, but problems related to the rapid degradation of C-peptide in blood and difficulty of 24-h urine collection have limited widespread routine clinical use of this test. We assessed the feasibility of measuring urinary C-peptide (UCP) with correction for creatinine concentration in single urine samples. Methods: We analyzed UCP using a routine electrochemiluminescence immunoassay in samples from 21 healthy volunteers. We investigated the stability of UCP with different preservatives and storage conditions and compared the reproducibility of urinary C-peptide/creatinine ratio (UCPCR) in first- and second-void fasting urines, then assessed correlations with 24-h collections. Results: UCPCR was unchanged at room temperature for 24 h and at 4 °C for 72 h even in the absence of preservative. UCPCR collected in boric acid was stable at room temperature for 72 h. UCPCR remained stable after 7 freeze-thaw cycles but decreased with freezer storage time and dropped to 82%–84% of baseline by 90 days at −20 °C. Second-void fasting UCPCRs were lower than first-void (median 0.78 vs 1.31, P = 0.0003) and showed less variation (CV 33% vs 52%), as second-void UCPCRs were not influenced by evening food-related insulin secretion. Second-void fasting UCPCR was highly correlated with 24-h UCP (r = 0.8, P = 0.00006). Conclusions: Second-void fasting UCPCR is a reproducible measure that correlates well with 24-h UCP in normal samples. The 3-day stability of UCPCR at room temperature greatly increases its potential clinical utility.