Genome-wide association study of offspring birth weight in 86 577 women identifies five novel loci and highlights maternal genetic effects that are independent of fetal genetics

Genome-wide association studies of birth weight have focused on fetal genetics, whereas relatively little is known about the role of maternal genetic variation. We aimed to identify maternal genetic variants associated with birth weight that could highlight potentially relevant maternal determinants of fetal growth. We meta-analysed data on up to 8.7 million SNPs in up to 86 577 women of European descent from the Early Growth Genetics (EGG) Consortium and the UK Biobank. We used structural equation modelling (SEM) and analyses of mother–child pairs to quantify the separate maternal and fetal genetic effects. Maternal SNPs at 10 loci (MTNR1B, HMGA2, SH2B3, KCNAB1, L3MBTL3, GCK, EBF1, TCF7L2, ACTL9, CYP3A7) were associated with offspring birth weight at P < 5 × 10⁻⁸. In SEM analyses, at least 7 of the 10 associations were consistent with effects of the maternal genotype acting via the intrauterine environment, rather than via effects of shared alleles with the fetus. Variants, or correlated proxies, at many of the loci had been previously associated with adult traits, including fasting glucose (MTNR1B, GCK and TCF7L2) and sex hormone levels (CYP3A7), and one (EBF1) with gestational duration. The identified associations indicate that genetic effects on maternal glucose, cytochrome P450 activity and gestational duration, and potentially on maternal blood pressure and immune function, are relevant for fetal growth. Further characterization of these associations in mechanistic and causal analyses will enhance understanding of the potentially modifiable maternal determinants of fetal growth, with the goal of reducing the morbidity and mortality associated with low and high birth weights.

IRX5 regulates adipocyte amyloid precursor protein and mitochondrial respiration in obesity

Objective

A causal obesity risk variant in the FTO locus was recently shown to inhibit adipocyte thermogenesis via increased adipose expression of the homeobox transcription factors IRX3 and IRX5. However, causal effects of IRX5 on fat storage remain to be shown in vivo, and discovery of downstream mediators may open new therapeutic avenues.

Methods

17 WT and 13 Irx5 knockout (KO) mice were fed low-fat control (Ctr) or high-fat (HF) diet for 10 weeks. Body weight, energy intake and fat mass were measured. Irx5-dependent gene expression was explored by transcriptome analysis of epididymal white adipose tissue (eWAT), confirmatory obesity-dependent expression in human adipocytes in vivo, and in vitro knock-down, overexpression and transcriptional activation assays.

Results

Irx5 knock-out mice weighed less, had diminished fat mass, and were protected from diet-induced fat accumulation. Key adipose mitochondrial genes Pparγ coactivator 1-alpha (Pgc-1α) and uncoupling protein 1 (Ucp1) were upregulated, and a gene network centered on amyloid precursor protein (App) was downregulated in adipose tissue of knock-out mice and in isolated mouse adipocytes with stable Irx5 knock-down. An APP-centered network was also enriched in isolated adipocytes from obese compared to lean humans. IRX5 overexpression increased APP promoter activity and both IRX5 and APP inhibited transactivation of PGC-1α and UCP1. Knock-down of Irx5 or App increased mitochondrial respiration in adipocytes.

Conclusion

Irx5-KO mice were protected from obesity and this can partially be attributed to reduced adipose App and improved mitochondrial respiration. This novel Irx5-App pathway in adipose tissue is a possible therapeutic entry point against obesity.

Parental Smoking and Risk of Childhood-onset Type 1 Diabetes

BACKGROUND

A few prospective studies suggest an association between maternal smoking during pregnancy and lower risk of type 1 diabetes. However, the role of unmeasured confounding and misclassification remains unclear.

METHODS

We comprehensively evaluated whether maternal smoking in pregnancy predicts lower risk of childhood-onset type 1 diabetes in two Scandinavian pregnancy cohorts (185,076 children; 689 cases) and a Norwegian register-based cohort (434,627 children; 692 cases). We measured cord blood cotinine as an objective marker of nicotine exposure during late pregnancy in 154 cases and 476 controls. We also examined paternal smoking during pregnancy, in addition to environmental tobacco smoke exposure the first 6 months of life, to clarify the role of characteristics of smokers in general.

RESULTS

In the pregnancy cohorts, maternal smoking beyond gestational week 12 was inversely associated with type 1 diabetes, pooled adjusted hazard ratio (aHR) 0.66 (95% CI = 0.51, 0.85). Similarly, in the Norwegian register-based cohort, children of mothers who still smoked at the end of pregnancy had lower risk of type 1 diabetes, aHR 0.65 (95% CI = 0.47, 0.89). Cord blood cotinine ≥30 nmol/L was also associated with reduced risk of type 1 diabetes, adjusted odds ratio 0.42 (95% CI = 0.17, 1.0). We observed no associations of paternal smoking during pregnancy, or environmental tobacco smoke exposure, with childhood-onset type 1 diabetes.

CONCLUSION

Maternal sustained smoking during pregnancy is associated with lower risk of type 1 diabetes in children. This sheds new light on the potential intrauterine environmental origins of the disease.

The mucinous domain of pancreatic carboxyl-ester lipase (CEL) contains core 1/core 2 O-glycans that can be modified by ABO blood group determinants

Carboxyl-ester lipase (CEL) is a pancreatic fat-digesting enzyme associated with human disease. Rare mutations in the CEL gene cause a syndrome of pancreatic exocrine and endocrine dysfunction denoted MODY8, whereas a recombined CEL allele increases the risk for chronic pancreatitis. Moreover, CEL has been linked to pancreatic ductal adenocarcinoma (PDAC) through a postulated oncofetal CEL variant termed feto-acinar pancreatic protein (FAPP). The monoclonal antibody mAb16D10 was previously reported to detect a glycotope in the highly O-glycosylated, mucin-like C terminus of CEL/FAPP. We here assessed the expression of human CEL in malignant pancreatic lesions and cell lines. CEL was not detectably expressed in neoplastic cells, implying that FAPP is unlikely to be a glycoisoform of CEL in pancreatic cancer. Testing of the mAb16D10 antibody in glycan microarrays then demonstrated that it recognized structures containing terminal GalNAc-α1,3(Fuc-α1,2)Gal (blood group A antigen) and also repeated protein sequences containing GalNAc residues linked to Ser/Thr (Tn antigen), findings that were supported by immunostainings of human pancreatic tissue. To examine whether the CEL glycoprotein might be modified by blood group antigens, we used high-sensitivity MALDI-TOF MS to characterize the released O-glycan pool of CEL immunoprecipitated from human pancreatic juice. We found that the O-glycome of CEL consisted mainly of core 1/core 2 structures with a composition depending on the subject's FUT2 and ABO gene polymorphisms. Thus, among digestive enzymes secreted by the pancreas, CEL is a glycoprotein with some unique characteristics, supporting the view that it could serve additional biological functions to its cholesteryl esterase activity in the duodenum.

Antibiotics, acetaminophen and infections during prenatal and early life in relation to type 1 diabetes

Background

Infections in early life have been linked to type 1 diabetes (T1D) risk, but no previous study has comprehensively analysed exposure to antibiotics, acetaminophen and infections during pregnancy and early childhood in relation to offspring risk of T1D.

Methods

Participants in the Norwegian Mother and Child Cohort Study (n = 114 215 children, of whom 403 children were diagnosed with T1D) reported infections and medication use through repeated questionnaires from pregnancy until the children were 18 months old. Adjusted hazard ratios (aHR) for offspring T1D were estimated through Cox regression adjusted for child's sex, maternal age and parity, maternal T1D, smoking in pregnancy, education level, pre-pregnancy body mass index (BMI) and birthweight. Antibiotic use was also analysed in a population-based register cohort of 541 036 children of whom 836 developed T1D.

Results

Hospitalization for gastroenteritis during the first 18 months of life was associated with increased risk (aHR 2.27, 95% CI 1.21 - 4.29, P = 0.01) of T1D. Childhood infections not requiring hospitalization, or any kind of maternal infection during pregnancy, did not predict offspring risk of T1D. Antibiotic or acetaminophen use in pregnancy, or child`s use in early childhood, was not associated with risk of T1D.

Conclusions

Our study, which is population-based and the largest of its kind, did not find support for general early life infections, infection frequency or use of antibiotics or acetaminophen to play a major role in childhood T1D. Hospital admission for gastroenteritis was associated with T1D risk, but must be interpreted cautiously due to scarcity of cases.

Effectiveness and safety of long-term treatment with sulfonylureas in patients with neonatal diabetes due to KCNJ11 mutations: an international cohort study

BACKGROUND

KCNJ11 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.

METHODS

In 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 HbA_1c and sulfonylurea dose. Neurological features associated with KCNJ11 permanent neonatal diabetes were also assessed. This study is registered with ClinicalTrials.gov, number NCT02624817.

FINDINGS

90 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 HbA_1c and sulfonylurea at all time points (ie, pre-transfer [for HbA_1c], year 1, and most recent follow-up; n=64)-median HbA_1c 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 sulfonylureas in 18 (47%) of 38 patients with CNS features. After long-term therapy with sulfonylureas, CNS features were seen in 52 (64%) of 81 patients.

INTERPRETATION

High-dose sulfonylurea therapy is an appropriate treatment for patients with KCNJ11 permanent neonatal diabetes from diagnosis. This therapy is safe and highly effective, maintaining excellent glycaemic control for at least 10 years.

FUNDING

Wellcome Trust, Diabetes UK, Royal Society, European Research Council, Norwegian Research Council, Kristian Gerhard Jebsen Foundation, Western Norway Regional Health Authority, Southern and Eastern Norway Regional Health Authority, Italian Ministry of Health, Aide aux Jeunes Diabetiques, Societe Francophone du Diabete, Ipsen, Slovak Research and Development Agency, and Research and Development Operational Programme funded by the European Regional Development Fund.

Mice Carrying a Dominant-Negative Human PI3K Mutation Are Protected From Obesity and Hepatic Steatosis but Not Diabetes

Phosphatidylinositol 3-kinase (PI3K) plays a central role in insulin signaling, glucose metabolism, cell growth, cell development, and apoptosis. A heterozygous missense mutation (R649W) in the p85α regulatory subunit gene of PI3K (PIK3R1) has been identified in patients with SHORT (Short stature, Hyperextensibility/Hernia, Ocular depression, Rieger anomaly, and Teething delay) syndrome, a disorder characterized by postnatal growth retardation, insulin resistance, and partial lipodystrophy. Knock-in mice with the same heterozygous mutation mirror the human phenotype. In this study, we show that Pik3r1 R649W knock-in mice fed a high-fat diet (HFD) have reduced weight gain and adipose accumulation. This is accompanied by reduced expression of several genes involved in lipid metabolism. Interestingly, despite the lower level of adiposity, the HFD knock-in mice are more hyperglycemic and more insulin-resistant than HFD-fed control mice. Likewise, when crossed with genetically obese ob/ob mice, the ob/ob mice carrying the heterozygous R649W mutation were protected from obesity and hepatic steatosis but developed a severe diabetic state. Together, our data demonstrate a central role of PI3K in development of obesity and fatty liver disease, separating these effects from the role of PI3K in insulin resistance and the resultant hyperglycemia.

Prenatal iron exposure and childhood type 1 diabetes

Iron overload due to environmental or genetic causes have been associated diabetes. We hypothesized that prenatal iron exposure is associated with higher risk of childhood type 1 diabetes. In the Norwegian Mother and Child cohort study (n = 94,209 pregnancies, n = 373 developed type 1 diabetes) the incidence of type 1 diabetes was higher in children exposed to maternal iron supplementation than unexposed (36.8/100,000/year compared to 28.6/100,000/year, adjusted hazard ratio 1.33, 95%CI: 1.06-1.67). Cord plasma biomarkers of high iron status were non-significantly associated with higher risk of type 1 diabetes (ferritin OR = 1.05 [95%CI: 0.99-1.13] per 50 mg/L increase; soluble transferrin receptor: OR = 0.91 [95%CI: 0.81-1.01] per 0.5 mg/L increase). Maternal but not fetal HFE genotypes causing high/intermediate iron stores were associated with offspring diabetes (odds ratio: 1.45, 95%CI: 1.04, 2.02). Maternal anaemia or non-iron dietary supplements did not significantly predict type 1 diabetes. Perinatal iron exposures were not associated with cord blood DNA genome-wide methylation, but fetal HFE genotype was associated with differential fetal methylation near HFE. Maternal cytokines in mid-pregnancy of the pro-inflammatory M1 pathway differed by maternal iron supplements and HFE genotype. Our results suggest that exposure to iron during pregnancy may be a risk factor for type 1 diabetes in the offspring.

Lack of Association Between Maternal or Neonatal Vitamin D Status and Risk of Childhood Type 1 Diabetes: A Scandinavian Case-Cohort Study

Studies on vitamin D status during pregnancy and risk of type 1 diabetes mellitus (T1D) lack consistency and are limited by small sample sizes or single measures of 25-hydroxyvitamin D (25(OH)D). We investigated whether average maternal 25(OH)D plasma concentrations during pregnancy are associated with risk of childhood T1D. In a case-cohort design, we identified 459 children with T1D and a random sample (n = 1,561) from the Danish National Birth Cohort (n = 97,127) and Norwegian Mother and Child Cohort Study (n = 113,053). Participants were born between 1996 and 2009. The primary exposure was the estimated average 25(OH)D concentration, based on serial samples from the first trimester until delivery and on umbilical cord plasma. We estimated hazard ratios using weighted Cox regression adjusting for multiple confounders. The adjusted hazard ratio for T1D per 10-nmol/L increase in the estimated average 25(OH)D concentration was 1.00 (95% confidence interval: 0.90, 1.10). Results were consistent in both cohorts, in multiple sensitivity analyses, and when we analyzed mid-pregnancy or cord blood separately. In conclusion, our large study demonstrated that normal variation in maternal or neonatal 25(OH)D is unlikely to have a clinically important effect on risk of childhood T1D.

Targets and teamwork: Understanding differences in pediatric diabetes centers treatment outcomes

OBJECTIVE

The reason for center differences in metabolic control of childhood diabetes is still unknown. We sought to determine to what extent the targets, expectations, and goals that diabetes care professionals have for their patients is a determinant of center differences in metabolic outcomes.

RESEARCH DESIGN AND METHODS

Children, under the age of 11 with type 1 diabetes and their parents treated at the study centers participated. Clinical, medical, and demographic data were obtained, along with blood sample for centralized assay. Parents and all members of the diabetes care team completed questionnaires on treatment targets for hemoglobin A1c (HbA1c) and recommended frequency of blood glucose monitoring.

RESULTS

Totally 1113 (53% male) children (mean age 8.0 ± 2.1 years) from 18 centers in 17 countries, along with parents and 113 health-care professionals, participated. There were substantial differences in mean HbA1c between centers ranging from 7.3 ± 0.8% (53 mmol/mol ± 8.7) to 8.9 ± 1.1% (74 mmol/mol ± 12.0). Centers with lower mean HbA1c had (1) parents who reported lower targets for their children, (2) health-care professionals that reported lower targets and more frequent testing, and (3) teams with less disagreement about recommended targets. Multiple regression analysis indicated that teams reporting higher HbA1c targets and more target disagreement had parents reporting higher treatment targets. This seemed to partially account for center differences in Hb1Ac.

CONCLUSIONS

The diabetes care teams' cohesiveness and perspectives on treatment targets, expectations, and recommendations have an influence on parental targets, contributing to the differences in pediatric diabetes center outcomes.

Publisher Correction: Protein-altering variants associated with body mass index implicate pathways that control energy intake and expenditure in obesity

In the version of this article originally published, one of the two authors with the name Wei Zhao was omitted from the author list and the affiliations for both authors were assigned to the single Wei Zhao in the author list. In addition, the ORCID for Wei Zhao (Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA) was incorrectly assigned to author Wei Zhou. The errors have been corrected in the HTML and PDF versions of the article.

Publisher Correction: Protein-altering variants associated with body mass index implicate pathways that control energy intake and expenditure in obesity

In the published version of this paper, the name of author Emanuele Di Angelantonio was misspelled. This error has now been corrected in the HTML and PDF versions of the article.

Paternal and maternal obesity but not gestational weight gain is associated with type 1 diabetes

Background

Our objective was to examine the associations of parental body mass index (BMI) and maternal gestational weight gain with childhood-onset type 1 diabetes. Comparing the associations of maternal and paternal BMI with type 1 diabetes in the offspring will provide further insight into the role of unmeasured confounding by characteristics linked to BMI in both parents.

Methods

We studied 132 331 children participating in the Norwegian Mother and Child Cohort Study (MoBa) and the Danish National Birth Cohort (DNBC) who were born between February 1998 and July 2009. Exposures of interest included parental BMI and maternal gestational weight gain obtained by maternal report. We used Cox-proportional hazards regression to examine the risk of type 1 diabetes (n=499 cases), which was ascertained by national childhood diabetes registers.

Results

The incidence of type 1 diabetes was 32.7 per 100 000 person-years in MoBa and 28.5 per 100 000 person-years in DNBC. Both maternal pre-pregnancy obesity, adjusted hazard ratio (HR) 1.41 [95% confidence interval (CI): 1.06, 1.89] and paternal obesity, adjusted HR 1.51 (95% CI: 1.11, 2.04), were associated with childhood-onset type 1 diabetes. The associations were similar after mutual adjustment. In contrast, maternal total gestational weight gain was not associated with childhood-onset type 1 diabetes, adjusted HR 1.00 (95% CI: 0.99, 1.02) per kilogram increase.

Conclusions

Our study suggests that the association between maternal obesity and childhood-onset type 1 diabetes is not likely explained by intrauterine mechanisms, but possibly rather by unknown environmental factors influencing BMI in the family.

The role of the carboxyl ester lipase (CEL) gene in pancreatic disease

The enzyme carboxyl ester lipase (CEL), also known as bile salt-dependent or -stimulated lipase (BSDL, BSSL), hydrolyzes dietary fat, cholesteryl esters and fat-soluble vitamins in the duodenum. CEL is mainly expressed in pancreatic acinar cells and lactating mammary glands. The human CEL gene resides on chromosome 9q34.3 and contains a variable number of tandem repeats (VNTR) region that encodes a mucin-like protein tail. Although the number of normal repeats does not appear to significantly influence the risk for pancreatic disease, single-base pair deletions in the first VNTR repeat cause a syndrome of endocrine and exocrine dysfunction denoted MODY8. Hallmarks are low fecal elastase levels and pancreatic lipomatosis manifesting before the age of twenty, followed by development of diabetes and pancreatic cysts later in life. The mutant protein forms intracellular and extracellular aggregates, suggesting that MODY8 is a protein misfolding disease. Recently, a recombined allele between CEL and its pseudogene CELP was discovered. This allele (CEL-HYB) encodes a chimeric protein with impaired secretion increasing five-fold the risk for chronic pancreatitis. The CEL gene has proven to be exceptionally polymorphic due to copy number variants of the CEL-CELP locus and alterations involving the VNTR. Genome-wide association studies or deep sequencing cannot easily pick up this wealth of genetic variation. CEL is therefore an attractive candidate gene for further exploration of links to pancreatic disease.

Protein-altering variants associated with body mass index implicate pathways that control energy intake and expenditure in obesity

Genome-wide association studies (GWAS) have identified >250 loci for body mass index (BMI), implicating pathways related to neuronal biology. Most GWAS loci represent clusters of common, noncoding variants from which pinpointing causal genes remains challenging. Here we combined data from 718,734 individuals to discover rare and low-frequency (minor allele frequency (MAF) < 5%) coding variants associated with BMI. We identified 14 coding variants in 13 genes, of which 8 variants were in genes (ZBTB7B, ACHE, RAPGEF3, RAB21, ZFHX3, ENTPD6, ZFR2 and ZNF169) newly implicated in human obesity, 2 variants were in genes (MC4R and KSR2) previously observed to be mutated in extreme obesity and 2 variants were in GIPR. The effect sizes of rare variants are ~10 times larger than those of common variants, with the largest effect observed in carriers of an MC4R mutation introducing a stop codon (p.Tyr35Ter, MAF = 0.01%), who weighed ~7 kg more than non-carriers. Pathway analyses based on the variants associated with BMI confirm enrichment of neuronal genes and provide new evidence for adipocyte and energy expenditure biology, widening the potential of genetically supported therapeutic targets in obesity.

Plasma immunological markers in pregnancy and cord blood: A possible link between macrophage chemo-attractants and risk of childhood type 1 diabetes

PROBLEM

Previous studies have suggested that immune perturbations during pregnancy can affect offspring type 1 diabetes (T1D) risk. We aimed to identify immunological markers that could predict offspring T1D or that were linked to T1D risk factors.

METHOD OF STUDY

We quantified selected circulating immunological markers in mid-pregnancy (interleukin [IL]-1β, IL-1ra, IL-2Rα, IL-2, -4, -5, -6, -10, -12p70, 13, -17A, GM-CSF, IFN-γ, CXCL10, CCL 2, CCL3, CCL4, TNF) and cord blood plasma (neopterin and kynurenine/tryptophan ratio) in a case-control study with 175 mother/child T1D cases (median age 5.8, range 0.7-13.0 years) and 552 controls.

RESULTS

Pre-pregnancy obesity was positively associated with CCL4, CXCL10, kynurenine/tryptophan ratio and neopterin (P < .01). The established T1D SNPs rs1159465 (near IL2RA) and rs75352297 (near CCR2 and CCR3) were positively associated with IL-2Rα and CCL4, respectively (P < .01). There was a borderline association of CCL4 and offspring T1D risk, independent of maternal obesity and genotype. When grouping the immunological markers, there was a borderline association (P = .05) with M1 phenotype and no association between M2-, Th1-, Th2- or Th17 phenotypes and offspring T1D risk.

CONCLUSION

Increased mid-pregnancy CCL4 levels showed borderline associations with increased offspring T1D risk, which may indicate a link between environmental factors in pregnancy and offspring T1D risk.

The HNF1A mutant Ala180Val: Clinical challenges in determining causality of a rare HNF1A variant in familial diabetes

AIMS

Heterozygous mutations in hepatocyte nuclear factor-1A (HNF1A) cause maturity-onset diabetes of the young type 3 (MODY3). Our aim was to compare two families with suspected dominantly inherited diabetes and a new HNF1A variant of unknown clinical significance.

METHODS

The HNF1A gene was sequenced in two independently recruited families from the Norwegian MODY Registry. Both familes were phenotyped clinically and biochemically. Microsatellite markers around and within the HNF1A locus were used for haplotyping. Chromosomal linkage analysis was performed in one family, and whole-exome sequencing was undertaken in two affected family members from each family. Transactivation activity, DNA binding and nuclear localization of wild type and mutant HNF-1A were assessed.

RESULTS

The novel HNF1A variant c.539C>T (p.Ala180Val) was found in both families. The variant fully co-segregated with diabetes in one family. In the other family, two subjects with diabetes mellitus and one with normal glucose levels were homozygous variant carriers. Chromosomal linkage of diabetes to the HNF1A locus or to other genomic regions could not be established. The protein functional studies did not reveal significant differences between wild type and variant HNF-1A. In each family, whole-exome sequencing failed to identify any other variant that could explain the disease.

CONCLUSIONS

The HNF1A variant p.Ala180Val does not seem to cause MODY3, although it may confer risk for type 2 diabetes mellitus. Our data demonstrate challenges in causality evaluation of rare variants detected in known diabetes genes.

The kynurenine:tryptophan ratio as a predictor of incident type 2 diabetes mellitus in individuals with coronary artery disease

AIMS/HYPOTHESIS

The tryptophan metabolite kynurenine has potent immune modulatory and vasoactive properties. Experimental data implicate kynurenine in obesity-related morbidities. Epidemiological studies are, however, sparse. We evaluated associations of the plasma and urine kynurenine:tryptophan ratio (KTR) to incident type 2 diabetes.

METHODS

We followed 2519 individuals with coronary artery disease (CAD; 73.1% men) without diabetes at baseline for a median of 7.6 years, during which 173 (6.9%) new incidences of type 2 diabetes were identified. Multivariate Cox regression analyses were applied to investigate the prospective relationships of plasma and urine KTR with new onset type 2 diabetes.

RESULTS

At inclusion, mean (SD) age was 61.3 (10.4) years, BMI was 25.9 (3.71) kg/m2 and median (interquartile range) HbA1c was 5.6% (5.0%-6.0%) (38 [31-42] mmol/mol). Plasma KTR was not significantly related to type 2 diabetes risk. By contrast, urine KTR showed a strong positive association. Comparing quartile 4 with quartile 1, the HRs (95% CIs) were 2.59 (1.56, 4.30) and 2.35 (1.39, 3.96) in the age- and sex-adjusted and multivariate models, respectively.

CONCLUSIONS/INTERPRETATION

Urine KTR is a strong predictor of incident type 2 diabetes in individuals with CAD. Potential clinical implications and possible pathogenic roles of renal kynurenine excretion in type 2 diabetes development should be further elucidated.

Iris Malformation and Anterior Segment Dysgenesis in Mice and Humans With a Mutation in PI 3-Kinase

Purpose

To determine the ocular consequences of a dominant-negative mutation in the p85α subunit of phosphatidylinositol 3-kinase (PIK3R1) using a knock-in mouse model of SHORT syndrome, a syndrome associated with short stature, lipodystrophy, diabetes, and Rieger anomaly in humans.

Methods

We investigated knock-in mice heterozygous for the SHORT syndrome mutation changing arginine 649 to tryptophan in p85α (PIK3R1) using physical examination, optical coherence tomography (OCT), tonometry, and histopathologic sections from paraffin-embedded eyes, and compared the findings to similar investigations in two human subjects with SHORT syndrome heterozygous for the same mutation.

Results

While overall eye development was normal with clear cornea and lens, normal anterior chamber volume, normal intraocular pressure, and no changes in the retinal structure, OCT images of the knock-in mouse eyes revealed a significant decrease in thickness and width of the iris resulting in increased pupil area and irregularity of shape. Both human subjects had Rieger anomaly with similar defects including thin irides and irregular pupils, as well as a prominent ring of Schwalbe, goniosynechiae, early cataract formation, and glaucoma. Although the two subjects had had diabetes for more than 30 years, there were no signs of diabetic retinopathy.

Conclusions

A dominant-negative mutation in the p85α regulatory subunit of PI3K affects development of the iris, and contributes to changes consistent with anterior segment dysgenesis in both humans and mice.

Infant Feeding and Risk of Type 1 Diabetes in Two Large Scandinavian Birth Cohorts

OBJECTIVE

Our aim was to study the relation between the duration of full and any breastfeeding and risk of type 1 diabetes.

RESEARCH DESIGN AND METHODS

We included two population-based cohorts of children followed from birth (1996-2009) to 2014 (Denmark) or 2015 (Norway). We analyzed data from a total of 155,392 children participating in the Norwegian Mother and Child Cohort Study (MoBa) and the Danish National Birth Cohort (DNBC). Parents reported infant dietary practices when their child was 6 and 18 months old. The outcome was clinical type 1 diabetes, ascertained from nationwide childhood diabetes registries. Hazard ratios (HRs) were estimated using Cox regression.

RESULTS

Type 1 diabetes was identified in 504 children during follow-up, and the incidence of type 1 diabetes per 100,000 person-years was 30.5 in the Norwegian cohort and 23.5 in the Danish cohort. Children who were never breastfed had a twofold increased risk of type 1 diabetes compared with those who were breastfed (HR 2.29 [95% CI 1.14-4.61] for no breastfeeding vs. any breastfeeding for ≥12 months). Among those who were breastfed, however, the incidence of type 1 diabetes was independent of duration of both full breastfeeding (HR per month 0.99 [95% CI 0.97-1.01]) and any breastfeeding (0.97 [0.92-1.03]).

CONCLUSIONS

Suggestive evidence supports the contention that breastfeeding reduces the risk of type 1 diabetes. Among those who were breastfed, however, no evidence indicated that prolonging full or any breastfeeding was associated with a reduced risk of type 1 diabetes.

Targeted next-generation sequencing reveals MODY in up to 6.5% of antibody-negative diabetes cases listed in the Norwegian Childhood Diabetes Registry

AIMS/HYPOTHESIS

MODY can be wrongly diagnosed as type 1 diabetes in children. We aimed to find the prevalence of MODY in a nationwide population-based registry of childhood diabetes.

METHODS

Using next-generation sequencing, we screened the HNF1A, HNF4A, HNF1B, GCK and INS genes in all 469 children (12.1%) negative for both GAD and IA-2 autoantibodies and 469 antibody-positive matched controls selected from the Norwegian Childhood Diabetes Registry (3882 children). Variants were classified using clinical diagnostic criteria for pathogenicity ranging from class 1 (neutral) to class 5 (pathogenic).

RESULTS

We identified 58 rare exonic and splice variants in cases and controls. Among antibody-negative patients, 6.5% had genetic variants of classes 3-5 (vs 2.4% in controls; p = 0.002). For the stricter classification (classes 4 and 5), the corresponding number was 4.1% (vs 0.2% in controls; p = 1.6 × 10^-5). HNF1A showed the strongest enrichment of class 3-5 variants, with 3.9% among antibody-negative patients (vs 0.4% in controls; p = 0.0002). Antibody-negative carriers of variants in class 3 had a similar phenotype to those carrying variants in classes 4 and 5.

CONCLUSIONS/INTERPRETATION

This is the first study screening for MODY in all antibody-negative children in a nationwide population-based registry. Our results suggest that the prevalence of MODY in antibody-negative childhood diabetes may reach 6.5%. One-third of these MODY cases had not been recognised by clinicians. Since a precise diagnosis is important for treatment and genetic counselling, molecular screening of all antibody-negative children should be considered in routine diagnostics.

Secretin-stimulated MRI assessment of exocrine pancreatic function in patients with cystic fibrosis and healthy controls

PURPOSE

Secretin-stimulated magnetic resonance imaging (s-MRI) and pancreatic diffusion weighted imaging (DWI) are novel non-invasive imaging techniques for assessment of exocrine pancreatic insufficiency (EPI). The aim was to validate s-MRI assessed pancreatic secreted volume using novel semi-automatic quantification software, and to assess the ability of s-MRI with DWI to diagnose EPI in patients with cystic fibrosis (CF).

METHODS

s-MRI and DWI was performed in 19 patients with CF (median age 21 years; range 16-56; eight men) and in 10 healthy controls (HC) (median age 46 years; range 20-65; four men). Sequential coronal T2-weighted images covering the duodenum and small bowel and axial DWI were acquired before and 1, 5, 9, and 13 min after secretin stimulation. A short endoscopic secretin test was used as reference method for EPI.

RESULTS

CF patients with EPI had lower apparent diffusion coefficient before secretin in the pancreatic head (P < 0.001) and lower secreted bowel fluid volumes (P = 0.035) compared to HC and CF patients without EPI. ROC curve analyses identified that secreted fluid volume after 13 min yielded the highest diagnostic accuracy for diagnosing EPI (AUC 0.93; 95% CI [0.80-1.00]).

CONCLUSION

Pancreatic s-MRI is useful for the assessment of exocrine pancreatic function with high diagnostic accuracy for the diagnosis of EPI in CF.

Rare and low-frequency coding variants alter human adult height

Height is a highly heritable, classic polygenic trait with approximately 700 common associated variants identified through genome-wide association studies so far. Here, we report 83 height-associated coding variants with lower minor-allele frequencies (in the range of 0.1-4.8%) and effects of up to 2 centimetres per allele (such as those in IHH, STC2, AR and CRISPLD2), greater than ten times the average effect of common variants. In functional follow-up studies, rare height-increasing alleles of STC2 (giving an increase of 1-2 centimetres per allele) compromised proteolytic inhibition of PAPP-A and increased cleavage of IGFBP-4 in vitro, resulting in higher bioavailability of insulin-like growth factors. These 83 height-associated variants overlap genes that are mutated in monogenic growth disorders and highlight new biological candidates (such as ADAMTS3, IL11RA and NOX4) and pathways (such as proteoglycan and glycosaminoglycan synthesis) involved in growth. Our results demonstrate that sufficiently large sample sizes can uncover rare and low-frequency variants of moderate-to-large effect associated with polygenic human phenotypes, and that these variants implicate relevant genes and pathways.

Serum Acylcarnitines and Risk of Cardiovascular Death and Acute Myocardial Infarction in Patients With Stable Angina Pectoris

Background

Excess levels of serum acylcarnitines, which are intermediate products in metabolism, have been observed in metabolic diseases such as type 2 diabetes mellitus. However, it is not known whether acylcarnitines may prospectively predict risk of cardiovascular death or acute myocardial infarction in patients with stable angina pectoris.

Methods and Results

This study included 4164 patients (median age, 62 years; 72% men). Baseline serum acetyl‐, octanoyl‐, palmitoyl‐, propionyl‐, and (iso)valerylcarnitine were measured using liquid chromatography/tandem mass spectrometry. Hazard ratios (HRs) and 95% CIs for quartile 4 versus quartile 1 are reported. The multivariable model included age, sex, body mass index, fasting status, current smoking, diabetes mellitus, apolipoprotein A1, apolipoprotein B, creatinine, left ventricular ejection fraction, extent of coronary artery disease, study center, and intervention with folic acid or vitamin B6. During median 10.2 years of follow‐up, 10.0% of the patients died of cardiovascular disease and 12.8% suffered a fatal or nonfatal acute myocardial infarction. Higher levels of the even‐chained acetyl‐, octanoyl‐, and palmitoyl‐carnitines were significantly associated with elevated risk of cardiovascular death, also after multivariable adjustments (HR [95% CI]: 1.52 [1.12, 2.06]; P=0.007; 1.73 [1.23, 2.44]; P=0.002; and 1.61 [1.18, 2.21]; P=0.003, respectively), whereas their associations with acute myocardial infarction were less consistent.

Conclusions

Among patients with suspected stable angina pectoris, elevated serum even‐chained acylcarnitines were associated with increased risk of cardiovascular death and, to a lesser degree with acute myocardial infarction, independent of traditional risk factors.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00354081.

Causes of death in childhood-onset Type 1 diabetes: long-term follow-up

AIMS

To assess the causes of death and cause-specific standardized mortality ratios in two nationwide, population-based cohorts diagnosed with Type 1 diabetes during the periods 1973-1982 and 1989-2012, and to evaluate changes in causes of death during the follow-up period.

METHODS

People with Type 1 diabetes who were aged < 15 years at diagnosis were identified in the Norwegian Childhood Diabetes Registry and followed from diagnosis until death, emigration or September 2013 (n = 7871). We assessed causes of death by linking data to the nationwide Cause of Death Registry and through a review committee that evaluated medical records, autopsy reports and death certificates.

RESULTS

During a mean (range) follow-up of 16.8 (0-40.7) years, 241 individuals (3.1%) died, representing 132 143 person-years. The leading cause of death before the age of 30 years was acute complications (41/119, 34.5%). After the age of 30 years cardiovascular disease was predominant (41/122, 33.6%), although death attributable to acute complications was still important in this age group (22/122, 18.0%). A total of 5% of deaths were caused by 'dead-in-bed' syndrome. The standardized mortality ratio was elevated for cardiovascular disease [11.9 (95% CI 8.6-16.4)] and violent death [1.7 (95% CI 1.3-2.1)] in both sexes combined, but was elevated for suicide only in women [2.5 (95% CI 1.2-5.3)]. The risk of death from acute complications was approximately half in women compared with men [hazard ratio 0.43 (95% CI 0.25-0.76)], and did not change with more recent year of diagnosis [hazard ratio 1.02 (0.98-1.05)].

CONCLUSIONS

There was no change in mortality attributable to acute complications during the study period. To reduce premature mortality in people with childhood-onset diabetes focus should be on prevention of acute complications. Male gender implied increased risk.

Copy number variants and VNTR length polymorphisms of the carboxyl-ester lipase (CEL) gene as risk factors in pancreatic cancer

BACKGROUND/OBJECTIVES

We have recently described copy number variants (CNVs) of the human carboxyl-ester lipase (CEL) gene, including a recombined deletion allele (CEL-HYB) that is a genetic risk factor for chronic pancreatitis. Associations with pancreatic disease have also been reported for the variable number of tandem repeat (VNTR) region located in CEL exon 11. Here, we examined if CEL CNVs and VNTR length polymorphisms affect the risk for developing pancreatic cancer.

METHODS

CEL CNVs and VNTR were genotyped in a German family with non-alcoholic chronic pancreatitis and pancreatic cancer, in 265 German and 197 Norwegian patients diagnosed with pancreatic adenocarcinoma, and in 882 controls. CNV screening was performed using PCR assays followed by agarose gel electrophoresis whereas VNTR lengths were determined by DNA fragment analysis.

RESULTS

The investigated family was CEL-HYB-positive. However, an association of CEL-HYB or a duplication CEL allele with pancreatic cancer was not seen in our two patient cohorts. The frequency of the 23-repeat VNTR allele was borderline significant in Norwegian cases compared to controls (1.2% vs. 0.3%; P = 0.05). For all other VNTR lengths, no statistically significant difference in frequency was observed. Moreover, no association with pancreatic cancer was detected when CEL VNTR lengths were pooled into groups of short, normal or long alleles.

CONCLUSIONS

We could not demonstrate an association between CEL CNVs and pancreatic cancer. An association is also unlikely for CEL VNTR lengths, although analyses in larger materials are necessary to completely exclude an effect of rare VNTR alleles.

Common and rare forms of diabetes mellitus: towards a continuum of diabetes subtypes

Insights into the genetic basis of type 2 diabetes mellitus (T2DM) have been difficult to discern, despite substantial research. More is known about rare forms of diabetes mellitus, several of which share clinical and genetic features with the common form of T2DM. In this Review, we discuss the extent to which the study of rare and low-frequency mutations in large populations has begun to bridge the gap between rare and common forms of diabetes mellitus. We hypothesize that the perceived division between these diseases might be due, in part, to the historical ascertainment bias of genetic studies, rather than a clear distinction between disease pathophysiologies. We also discuss possible implications of a new model for the genetic basis of diabetes mellitus subtypes, where the boundary between subtypes becomes blurred.

The Hypoglycemic Phenotype Is Islet Cell-Autonomous in Short-Chain Hydroxyacyl-CoA Dehydrogenase-Deficient Mice

Congenital hyperinsulinism of infancy (CHI) can be caused by inactivating mutations in the gene encoding short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD), a ubiquitously expressed enzyme involved in fatty acid oxidation. The hypersecretion of insulin may be explained by a loss of interaction between SCHAD and glutamate dehydrogenase in the pancreatic β-cells. However, there is also a general accumulation of metabolites specific for the enzymatic defect in affected individuals. It remains to be explored whether hypoglycemia in SCHAD CHI can be uncoupled from the systemic effect on fatty acid oxidation. We therefore transplanted islets from global SCHAD knockout (SCHADKO) mice into mice with streptozotocin-induced diabetes. After transplantation, SCHADKO islet recipients exhibited significantly lower random and fasting blood glucose compared with mice transplanted with normal islets or nondiabetic, nontransplanted controls. Furthermore, intraperitoneal glucose tolerance was improved in animals receiving SCHADKO islets compared with those receiving normal islets. Graft β-cell proliferation and apoptosis rates were similar in the two transplantation groups. We conclude that hypoglycemia in SCHAD-CHI is islet cell-autonomous.

Prospective Associations of Systemic and Urinary Choline Metabolites with Incident Type 2 Diabetes

BACKGROUND

Several compounds in the choline oxidation pathway are associated with insulin resistance and prevalent diabetes; however, prospective data are scarce.

We explored the relationships between systemic and urinary choline-related metabolites and incident type 2 diabetes in an observational prospective study among Norwegian patients.

METHODS

We explored risk associations by logistic regression among 3621 nondiabetic individuals with suspected stable angina pectoris, of whom 3242 provided urine samples. Reclassification of patients was investigated according to continuous net reclassification improvement (NRI &gt;0).

RESULTS

After median (25th to 75th percentile) follow-up of 7.5 (6.4–8.7) years, 233 patients (6.4%) were registered with incident type 2 diabetes. In models adjusted for age, sex, and fasting status, plasma betaine was inversely related to new-onset disease [odds ratio (OR) per 1 SD, 0.72; 95% CI, 0.62–0.83; P &lt; 0.00001], whereas positive associations were observed for urine betaine (1.25; 1.09–1.43; P = 0.001), dimethylglycine (1.22; 1.06–1.40; P = 0.007), and sarcosine (1.30; 1.13–1.49; P &lt; 0.001). The associations were maintained in a multivariable model adjusting for body mass index, hemoglobin A1c, urine albumin-to-creatinine ratio, estimated glomerular filtration rate, C-reactive protein, HDL cholesterol, and medications. Plasma betaine and urine sarcosine, the indices most strongly related to incident type 2 diabetes, improved reclassification [NRI &gt;0 (95% CI) 0.33 (0.19–0.47) and 0.16 (0.01–0.31), respectively] and showed good within-person reproducibility.

CONCLUSIONS

Systemic and urinary concentrations of several choline metabolites were associated with risk of incident type 2 diabetes, and relevant biomarkers may improve risk prediction.

PI3-kinase mutation linked to insulin and growth factor resistance in vivo

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is central to the action of insulin and many growth factors. Heterozygous mutations in the gene encoding the p85α regulatory subunit of PI3K (PIK3R1) have been identified in patients with SHORT syndrome - a disorder characterized by short stature, partial lipodystrophy, and insulin resistance. Here, we evaluated whether SHORT syndrome-associated PIK3R1 mutations account for the pathophysiology that underlies the abnormalities by generating knockin mice that are heterozygous for the Pik3r1Arg649Trp mutation, which is homologous to the mutation found in the majority of affected individuals. Similar to the patients, mutant mice exhibited a reduction in body weight and length, partial lipodystrophy, and systemic insulin resistance. These derangements were associated with a reduced capacity of insulin and other growth factors to activate PI3K in liver, muscle, and fat; marked insulin resistance in liver and fat of mutation-harboring animals; and insulin resistance in vitro in cells derived from these mice. In addition, mutant mice displayed defective insulin secretion and GLP-1 action on islets in vivo and in vitro. These data demonstrate the ability of this heterozygous mutation to alter PI3K activity in vivo and the central role of PI3K in insulin/growth factor action, adipocyte function, and glucose metabolism.

Structure-function studies of HNF1A (MODY3) gene mutations in South Indian patients with monogenic diabetes

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic form of diabetes characterized by onset of diabetes below 25 years of age, autosomal dominant mode of inheritance and primary defect in insulin secretion. Mutations in the gene (HNF1A) encoding transcription factor hepatocyte nuclear factor 1A (HNF-1A) results in one of the most common forms of MODY (MODY3). HNF-1A is mainly enriched in pancreatic β-cells and hepatocytes and important for organ development and normal pancreatic function. We here report on the functional interrogation of eight missense HNF1A mutations associated with MODY3 in South Indian subjects, and the contributing effect of common variant (S487N) within HNF1A. Of the eight mutations, three mutations (p.R171G, p.G245R and p.R263H), in particular, affected HNF-1A function in transfected HeLa cells by reducing both transcriptional activity and nuclear localization, possibly due to disruption of the integrity of the three dimensional structure. The common variant p.S487N contributed further to the loss-of-function of p.R271Q (p.R271Q+p.S487N double mutant), in vitro, on both activity and localization. Our data on the first functional study of HNF1A mutations in South India subjects confers that the defect of the HNF-1A mutant proteins are responsible for MODY3 diabetes in these patients.

High Incidence of Heterozygous ABCC8 and HNF1A Mutations in Czech Patients With Congenital Hyperinsulinism

CONTEXT

Congenital hyperinsulinism of infancy (CHI) represents a group of heterogeneous disorders characterized by oversecretion of insulin from pancreatic β-cells causing severe hypoglycemia.

OBJECTIVE

We studied the distribution of genetic causes of CHI in a Czech population.

METHODS

Countrywide collection of patients with CHI included 40 subjects (12 females, median age of diagnosis, 1 wk [interquartile range, 1-612 wk]). We sequenced the ABCC8, KCNJ11, GLUD1, GCK, HADH, UCP2, SLC16A1, HNF4A, and HNF1A genes and investigated structural changes in the ABCC8 gene. We functionally tested novel variants in the ABCC8 gene by Rb(86+) efflux assay and novel variants in the HNF1A gene by transcriptional activation and DNA-binding tests.

RESULTS

We found causal mutations in 20 subjects (50%): 19 carried a heterozygous mutation while one patient was homozygous for mutation in the ABCC8 gene. Specifically, we detected 11 mutations (seven novel) in ABCC8, one novel mutation in KCNJ11, five mutations (two novel) in HNF1A, two novel mutations in HNF4A, and one in GCK. We showed a decrease of activation by diazoxide in mutant KATP channels with novel ABCC8 variants by 41-91% (median, 82%) compared with wild-type (WT) channels and reduced transcriptional activity of mutant HNF1A proteins (2.9% for p.Asn62Lysfs93* and 22% for p.Leu254Gln) accompanied by no DNA-binding ability compared with WT HNF1A.

CONCLUSION

We detected a higher proportion of heterozygous mutations causing CHI compared with other cohorts probably due to lack of consanguinity and inclusion of milder CHI forms. Interestingly, HNF1A gene mutations represented the second most frequent genetic cause of CHI in the Czech Republic. Based on our results we present a genetic testing strategy specific for similar populations.

Clinical reappraisal of SHORT syndrome with PIK3R1 mutations: toward recommendation for molecular testing and management

SHORT syndrome has historically been defined by its acronym: short stature (S), hyperextensibility of joints and/or inguinal hernia (H), ocular depression (O), Rieger abnormality (R) and teething delay (T). More recently several research groups have identified PIK3R1 mutations as responsible for SHORT syndrome. Knowledge of the molecular etiology of SHORT syndrome has permitted a reassessment of the clinical phenotype. The detailed phenotypes of 32 individuals with SHORT syndrome and PIK3R1 mutation, including eight newly ascertained individuals, were studied to fully define the syndrome and the indications for PIK3R1 testing. The major features described in the SHORT acronym were not universally seen and only half (52%) had four or more of the classic features. The commonly observed clinical features of SHORT syndrome seen in the cohort included intrauterine growth restriction (IUGR) <10th percentile, postnatal growth restriction, lipoatrophy and the characteristic facial gestalt. Anterior chamber defects and insulin resistance or diabetes were also observed but were not as prevalent. The less specific, or minor features of SHORT syndrome include teething delay, thin wrinkled skin, speech delay, sensorineural deafness, hyperextensibility of joints and inguinal hernia. Given the high risk of diabetes mellitus, regular monitoring of glucose metabolism is warranted. An echocardiogram, ophthalmological and hearing assessments are also recommended.

All-cause mortality in a nationwide cohort of childhood-onset diabetes in Norway 1973-2013

AIMS/HYPOTHESIS

The aim of this study was to assess the association between all-cause mortality and sex, age at diagnosis and year of diagnosis in Norwegian patients with childhood-onset diabetes.

METHODS

The study was based on the nationwide, population-based Norwegian Childhood Diabetes Registry, which includes all newly diagnosed cases of childhood-onset diabetes at age 0-14 years in 1973-1982 and 1989-2012 (n = 7,884). Patients were followed until date of death, emigration or 30 September 2013.

RESULTS

Among the 7,884 patients, representing 132,420 person-years, 249 (3.2%) died during a mean follow-up of 16.8 (range 0.0-40.7) years. The standardised mortality ratio (SMR) for the total cohort was 3.6 (95% CI 3.1, 4.0), increasing by attained age. Absolute mortality was significantly lower in females than in males (HR 0.50 [95% CI 0.38, 0.65]), although the SMRs were similar. Cox regression analysis showed a significant decrease in mortality of 49% (HR 0.51 [95% CI 0.28, 0.93]) for those diagnosed in 1999-2012 compared with those diagnosed in 1973-1982 (p = 0.03).

CONCLUSIONS/INTERPRETATION

In spite of improved diabetes care, mortality is still three to four times higher in those with childhood-onset diabetes compared with the general population in Norway. However, absolute mortality has declined among children diagnosed most recently (1999-2012) compared with those diagnosed in the earliest period (1973-1982).

Glycogenin-2 is dispensable for liver glycogen synthesis and glucagon-stimulated glucose release

CONTEXT

The synthesis of glycogen is initiated by glycogenin. In humans, glycogenin-1 is expressed ubiquitously, whereas glycogenin-2 (GN2) is highly expressed in liver. It has therefore been suggested that GN2 is a liver isoform of glycogenin. In a search for possible copy number variations associated with monogenic diabetes, we identified a 102-kb deletion of the X chromosome involving the entire GYG2 gene (encoding GN2) in 2 families.

OBJECTIVE

The purpose of this study was to test whether male GYG2 deletion carriers had abnormal glucose metabolism and/or glycogen synthesis.

DESIGN, SETTING, AND PATIENTS

Two families with diabetes and a GYG2 deletion were investigated with medical history and examination, glucagon stimulation tests, and liver biopsies.

RESULTS

We identified a GYG2 deletion in 3 members of family 1, 8 members of family 2, and 1 blood donor. The deletion showed no clear cosegregation with diabetes. Deletion carriers reported no symptoms related to fasting. Results of cardiac examination and abdominal ultrasound imaging were normal. A glucagon stimulation test in 4 male deletion carriers showed a mean rise in plasma glucose of 3.6 mmol/L (95% confidence interval, 2.9-4.2) compared with 2.8 mmol/L (95% confidence interval, 2.2-3.4) in control subjects. Liver biopsy specimens did not show clear morphologic changes by light microscopy and showed the presence of both α- and β-glycogen by electron microscopy. We detected GYG1 but not GYG2 mRNA expression in the liver biopsy specimens.

CONCLUSIONS

This is the first evaluation of humans without GN2 expression. Our data indicate that GN2 is not required for liver glycogen synthesis and glucagon-stimulated glucose release.

A recombined allele of the lipase gene CEL and its pseudogene CELP confers susceptibility to chronic pancreatitis

Carboxyl-ester lipase is a digestive pancreatic enzyme encoded by the highly polymorphic CEL gene¹. Mutations in CEL cause maturity-onset diabetes of the young (MODY) with pancreatic exocrine dysfunction². Here we identified a hybrid allele (CEL-HYB), originating from a crossover between CEL and its neighboring pseudogene CELP. In a discovery cohort of familial chronic pancreatitis cases, the carrier frequency of CEL-HYB was 14.1% (10/71) compared with 1.0% (5/478) in controls (odds ratio [OR] = 15.5, 95% confidence interval [CI] = 5.1-46.9, P = 1.3 × 10⁻⁶). Three replication studies in non-alcoholic chronic pancreatitis cohorts identified CEL-HYB in a total of 3.7% (42/1,122) cases and 0.7% (30/4,152) controls (OR = 5.2, 95% CI = 3.2-8.5, P = 1.2 × 10⁻¹¹; formal meta-analysis). The allele was also enriched in alcoholic chronic pancreatitis. Expression of CEL-HYB in cellular models revealed reduced lipolytic activity, impaired secretion, prominent intracellular accumulation and induced autophagy. The hybrid variant of CEL is the first chronic pancreatitis gene identified outside the protease/antiprotease system of pancreatic acinar cells.

The Chromosome 9p21 CVD- and T2D-Associated Regions in a Norwegian Population (The HUNT2 Survey)

Background. Two adjacent regions upstream CDKN2B on chromosome 9p21 have been associated with type 2 diabetes (T2D) and progression of cardiovascular disease (CVD). The precise location and number of risk variants have not been completely delineated and a possible synergistic relationship between the adjacent regions is not fully addressed. By a population based cross-sectional case-control design, we genotyped 18 SNPs upstream of CDKN2B tagging 138 kb in and around two LD-blocks associated with CVD and T2D and investigated associations with T2D, angina pectoris (AP), myocardial infarction (MI), coronary heart disease (CHD; AP or AMI), and stroke using 5,564 subjects from HUNT2. Results. Single point and haplotype analysis showed evidence for only one common T2D risk haplotype (rs10757282∣rs10811661: OR = 1.19, P = 2.0 × 10(-3)) in the region. We confirmed the strong association between SNPs in the 60 kb CVD region with AP, MI, and CHD (P < 0.01). Conditioning on the lead SNPs in the region, we observed two suggestive independent single SNP association signals for MI, rs2065501  (P = 0.03) and rs3217986  (P = 0.04). Conclusions. We confirmed the association of known variants within the 9p21 interval with T2D and CHD. Our results further suggest that additional CHD susceptibility variants exist in this region.

Endocytosis of secreted carboxyl ester lipase in a syndrome of diabetes and pancreatic exocrine dysfunction

Maturity-onset diabetes of the young, type 8 (MODY8) is characterized by a syndrome of autosomal dominantly inherited diabetes and exocrine pancreatic dysfunction. It is caused by deletion mutations in the last exon of the carboxyl ester lipase (CEL) gene, resulting in a CEL protein with increased tendency to aggregate. In this study we investigated the intracellular distribution of the wild type (WT) and mutant (MUT) CEL proteins in cellular models. We found that both CEL-WT and CEL-MUT were secreted via the endoplasmic reticulum and Golgi compartments. However, their subcellular distributions differed, as only CEL-MUT was observed as an aggregate at the cell surface and inside large cytoplasmic vacuoles. Many of the vacuoles were identified as components of the endosomal system, and after its secretion, the mutant CEL protein was re-internalized, transported to the lysosomes, and degraded. Internalization of CEL-MUT also led to reduced viability of pancreatic acinar and beta cells. These findings may have implications for the understanding of how the acinar-specific CEL-MUT protein causes both exocrine and endocrine pancreatic disease.

Association of a low-frequency variant in HNF1A with type 2 diabetes in a Latino population

IMPORTANCE

Latino populations have one of the highest prevalences of type 2 diabetes worldwide.

OBJECTIVES

To investigate the association between rare protein-coding genetic variants and prevalence of type 2 diabetes in a large Latino population and to explore potential molecular and physiological mechanisms for the observed relationships.

DESIGN, SETTING, AND PARTICIPANTS

Whole-exome sequencing was performed on DNA samples from 3756 Mexican and US Latino individuals (1794 with type 2 diabetes and 1962 without diabetes) recruited from 1993 to 2013. One variant was further tested for allele frequency and association with type 2 diabetes in large multiethnic data sets of 14,276 participants and characterized in experimental assays.

MAIN OUTCOME AND MEASURES

Prevalence of type 2 diabetes. Secondary outcomes included age of onset, body mass index, and effect on protein function.

RESULTS

A single rare missense variant (c.1522G>A [p.E508K]) was associated with type 2 diabetes prevalence (odds ratio [OR], 5.48; 95% CI, 2.83-10.61; P = 4.4 × 10(-7)) in hepatocyte nuclear factor 1-α (HNF1A), the gene responsible for maturity onset diabetes of the young type 3 (MODY3). This variant was observed in 0.36% of participants without type 2 diabetes and 2.1% of participants with it. In multiethnic replication data sets, the p.E508K variant was seen only in Latino patients (n = 1443 with type 2 diabetes and 1673 without it) and was associated with type 2 diabetes (OR, 4.16; 95% CI, 1.75-9.92; P = .0013). In experimental assays, HNF-1A protein encoding the p.E508K mutant demonstrated reduced transactivation activity of its target promoter compared with a wild-type protein. In our data, carriers and noncarriers of the p.E508K mutation with type 2 diabetes had no significant differences in compared clinical characteristics, including age at onset. The mean (SD) age for carriers was 45.3 years (11.2) vs 47.5 years (11.5) for noncarriers (P = .49) and the mean (SD) BMI for carriers was 28.2 (5.5) vs 29.3 (5.3) for noncarriers (P = .19).

CONCLUSIONS AND RELEVANCE

Using whole-exome sequencing, we identified a single low-frequency variant in the MODY3-causing gene HNF1A that is associated with type 2 diabetes in Latino populations and may affect protein function. This finding may have implications for screening and therapeutic modification in this population, but additional studies are required.

Loss-of-function mutations in SLC30A8 protect against type 2 diabetes

Loss-of-function mutations protective against human disease provide in vivo validation of therapeutic targets, but none have yet been described for type 2 diabetes (T2D). Through sequencing or genotyping of ~150,000 individuals across 5 ancestry groups, we identified 12 rare protein-truncating variants in SLC30A8, which encodes an islet zinc transporter (ZnT8) and harbors a common variant (p.Trp325Arg) associated with T2D risk and glucose and proinsulin levels. Collectively, carriers of protein-truncating variants had 65% reduced T2D risk (P = 1.7 × 10(-6)), and non-diabetic Icelandic carriers of a frameshift variant (p.Lys34Serfs*50) demonstrated reduced glucose levels (-0.17 s.d., P = 4.6 × 10(-4)). The two most common protein-truncating variants (p.Arg138* and p.Lys34Serfs*50) individually associate with T2D protection and encode unstable ZnT8 proteins. Previous functional study of SLC30A8 suggested that reduced zinc transport increases T2D risk, and phenotypic heterogeneity was observed in mouse Slc30a8 knockouts. In contrast, loss-of-function mutations in humans provide strong evidence that SLC30A8 haploinsufficiency protects against T2D, suggesting ZnT8 inhibition as a therapeutic strategy in T2D prevention.

GCK-MODY diabetes as a protein misfolding disease: the mutation R275C promotes protein misfolding, self-association and cellular degradation

GCK-MODY, dominantly inherited mild hyperglycemia, is associated with more than 600 mutations in the glucokinase gene. Different molecular mechanisms have been shown to explain GCK-MODY. Here, we report a Pakistani family harboring the glucokinase mutation c.823C>T (p.R275C). The recombinant and in cellulo expressed mutant pancreatic enzyme revealed slightly increased enzyme activity (kcat) and normal affinity for α-D-glucose, and resistance to limited proteolysis by trypsin comparable with wild-type. When stably expressed in HEK293 cells and MIN6 β-cells (at different levels), the mutant protein appeared misfolded and unstable with a propensity to form dimers and aggregates. Its degradation rate was increased, involving the lysosomal and proteasomal quality control systems. On mutation, a hydrogen bond between the R275 side-chain and the carbonyl oxygen of D267 is broken, destabilizing the F260-L271 loop structure and the protein. This promotes the formation of dimers/aggregates and suggests that an increased cellular degradation is the molecular mechanism by which R275C causes GCK-MODY.

Carboxyl-ester lipase maturity-onset diabetes of the young is associated with development of pancreatic cysts and upregulated MAPK signaling in secretin-stimulated duodenal fluid

Carboxyl-ester lipase (CEL) maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes and pancreatic exocrine dysfunction due to mutations in the CEL gene encoding CEL. The pathogenic mechanism for diabetes development is unknown. Since CEL is expressed mainly in pancreatic acinar cells, we asked whether we could find structural pancreatic changes in CEL-MODY subjects during the course of diabetes development. Furthermore, we hypothesized that the diseased pancreas releases proteins that are detectable in pancreatic fluid and potentially reflect activation or inactivation of disease-specific pathways. We therefore investigated nondiabetic and diabetic CEL-mutation carriers by pancreatic imaging studies and secretin-stimulated duodenal juice sampling. The secretin-stimulated duodenal juice was studied using cytokine assays, mass spectrometry (MS) proteomics, and multiplexed MS-based measurement of kinase activities. We identified multiple pancreatic cysts in all eight diabetic mutation carriers but not in any of the four nondiabetic mutation carriers or the six healthy controls. Furthermore, we identified upregulated mitogen-activated protein kinase (MAPK) target proteins and MAPK-driven cytokines and increased MAPK activity in the secretin-stimulated duodenal juice. These findings show that subjects with CEL-MODY develop multiple pancreatic cysts by the time they develop diabetes and that upregulated MAPK signaling in the pancreatic secretome may reflect the pathophysiological development of pancreatic cysts and diabetes.

A novel GATA6 mutation in a child with congenital heart malformation and neonatal diabetes

KEY CLINICAL MESSAGE

Diabetes in neonates is a monogenetic disease and genetic analysis is warranted to allow best treatment, prognosis, and genetic counseling. Transcription factor mutations may have a variable expression and different organs may be involved.

Exocrine pancreatic function in hepatocyte nuclear factor 1β-maturity-onset diabetes of the young (HNF1B-MODY) is only moderately reduced: compensatory hypersecretion from a hypoplastic pancreas

OBJECTIVES

To examine the exocrine pancreatic function in carriers of the hepatocyte nuclear factor 1β gene (HNF1B) mutation by direct testing.

METHODS

Patients with HNF1B mutations and control subjects were assessed using rapid endoscopic secretin tests and secretin-stimulated magnetic resonance imaging. Seven patients and 25 controls underwent endoscopy, while eight patients and 20 controls had magnetic resonance imaging. Ductal function was assessed according to peak bicarbonate concentrations and acinar function was assessed according to peak digestive enzyme activities in secretin-stimulated duodenal juice. The association of pancreatic exocrine function and diabetes status with pancreatic gland volume was examined.

RESULTS

The mean increase in secretin-stimulated duodenal fluid was smaller in patients than controls (4.0 vs 6.4 ml/min; P = 0.003). We found lower ductal function in patients than controls (median peak bicarbonate concentration: 73 vs 116 mEq/L; P < 0.001) and lower acinar function (median peak lipase activity: 6.4 vs 33.5 kU/ml; P = 0.01; median peak elastase activity: 0.056 vs 0.130 U/ml; P = 0.01). Pancreatic fluid volume outputs correlated significantly with pancreatic gland volumes (r² = 0.71, P = 0.008) in patients. The total fluid output to pancreatic gland volume ratios were higher in patients than controls (4.5 vs 1.3 ml/cm³; P = 0.03), suggesting compensatory hypersecretion in the remaining gland.

CONCLUSION

Carriers of the HNF1B mutation have lower exocrine pancreatic function involving both ductal and acinar cells. Compensatory hypersecretion suggests that the small pancreas of HNF1B mutation carriers is attributable to hypoplasia, not atrophy.

Prevalence of monogenic diabetes in the population-based Norwegian Childhood Diabetes Registry

AIMS/HYPOTHESIS

Monogenic diabetes (MD) might be misdiagnosed as type 1 diabetes. The prevalence of MD among children with apparent type 1 diabetes has not been established. Our aim was to estimate the prevalence of common forms of MD in childhood diabetes.

METHODS

We investigated 2,756 children aged 0-14 years with newly diagnosed diabetes who had been recruited to the nationwide population-based Norwegian Childhood Diabetes Registry (NCDR), from July 2002 to March 2012. Completeness of ascertainment was 91%. Children diagnosed with diabetes who were under12 months of age were screened for mutations in KCNJ11, ABCC8 and INS. Children without GAD and protein tyrosine phosphatase-like protein antibodies were screened in two ways. Those who had a parent with diabetes were screened for mutations in HNF1A, HNF4A, INS and MT-TL1. Children with HbA1c <7.5% (<58 mmol/mol) and no insulin requirement were screened for mutations in GCK. Finally, we searched the Norwegian MODY Registry for children with genetically verified MD.

RESULTS

We identified 15 children harbouring a mutation in HNF1A, nine with one in GCK, four with one in KCNJ11, one child with a mutation in INS and none with a mutation in MT-TL1. The minimum prevalence of MD in the NCDR was therefore 1.1%. By searching the Norwegian MODY Registry, we found 24 children with glucokinase-MODY, 15 of whom were not present in the NCDR. We estimated the minimum prevalence of MD among Norwegian children to be 3.1/100,000.

CONCLUSIONS/INTERPRETATION

This is the first prevalence study of the common forms of MD in a nationwide, population-based registry of childhood diabetes. We found that 1.1% of patients in the Norwegian Childhood Diabetes Registry had MD.

Type 2 diabetes genes – Present status and data from Norwegian studies

The worldwide rise in prevalence of type 2 diabetes has led to an intense search for the genetic risk factors of this disease. In type 2 diabetes and other complex disorders, multiple genetic and environmental factors, as well as the interaction between these factors, determine the phenotype. In this review, we summarize present knowledge, generated by more than two decades of efforts to dissect the genetic architecture of type 2 diabetes. Initial studies were either based on a candidate gene approach or attempted to fine-map signals generated from linkage analysis. Despite the detection of multiple genomic regions proposed to be linked to type 2 diabetes, subsequent positional fine-mapping of candidates were mostly inconclusive. However, the introduction of genome-wide association studies (GWAS), applied on thousands of patients and controls, completely changed the field. To date, more than 50 susceptibility loci for type 2 diabetes have been detected through the establishment of large research consortia, the application of GWAS on intermediary diabetes phenotypes and the use of study samples of different ethnicities. Still, the common variants identified in the GWAS era only explain some of the heritability seen for type 2 diabetes. Thus, focus is now shifting towards searching also for rare variants using new high-throughput sequencing technologies. For genes involved in the genetic predisposition to type 2 diabetes the emerging picture is that there are hundreds of different gene variants working in a complex interplay influencing pancreatic beta cell function/mass and, only to a lesser extent, insulin action. Several Norwegian studies have contributed to the field, extending our understanding of genetic risk factors in type 2 diabetes and in diabetes-related phenotypes like obesity and cardiovascular disease.