Helge Ræder

Mutations in the CEL VNTR cause a syndrome of diabetes and pancreatic exocrine dysfunction.

Dysfunction of the exocrine pancreas is observed in diabetes, but links between concurrent exocrine and endocrine pancreatic disease and contributing genetic factors are poorly characterized. We studied two families with diabetes and exocrine pancreatic dysfunction by genetic, physiological and in vitro functional studies. A genome-wide screen in Family 1 linked diabetes to chromosome 9q34 (maximal lod score 5.07). Using fecal elastase deficiency as a marker of exocrine pancreatic dysfunction refined the critical chromosomal region to 1.16 Mb (maximal lod score 11.6). Here, we identified a single-base deletion in the variable number of tandem repeats (VNTR)-containing exon 11 of the carboxyl ester lipase (CEL) gene, a major component of pancreatic juice and responsible for the duodenal hydrolysis of cholesterol esters. Screening subjects with maturity-onset diabetes of the young identified Family 2, with another single-base deletion in CEL and a similar phenotype with beta-cell failure and pancreatic exocrine disease. The in vitro catalytic activities of wild-type and mutant CEL protein were comparable. The mutant enzyme was, however, less stable and secreted at a lower rate. Furthermore, we found some evidence for an association between common insertions in the CEL VNTR and exocrine dysfunction in a group of 182 unrelated subjects with diabetes (odds ratio 4.2 (1.6, 11.5)). Our findings link diabetes to the disrupted function of a lipase in the pancreatic acinar cells.

Mutations in the Insulin Gene Can Cause MODY and Autoantibody-Negative Type 1 Diabetes

OBJECTIVE—Mutations in the insulin (INS) gene can cause neonatal diabetes. We hypothesized that mutations in INS could also cause maturity-onset diabetes of the young (MODY) and autoantibody-negative type 1 diabetes. RESEARCH DESIGN AND METHODS—We screened INS in 62 probands with MODY, 30 probands with suspected MODY, and 223 subjects from the Norwegian Childhood Diabetes Registry selected on the basis of autoantibody negativity or family history of diabetes. RESULTS—Among the MODY patients, we identified the INS mutation c.137G>A (R46Q) in a proband, his diabetic father, and a paternal aunt. They were diagnosed with diabetes at 20, 18, and 17 years of age, respectively, and are treated with small doses of insulin or diet only. In type 1 diabetic patients, we found the INS mutation c.163C>T (R55C) in a girl who at 10 years of age presented with ketoacidosis and insulin-dependent, GAD, and insulinoma-associated antigen-2 (IA-2) antibody-negative diabetes. Her mother had a de novo R55C mutation and was diagnosed with ketoacidosis and insulin-dependent diabetes at 13 years of age. Both had residual β-cell function. The R46Q substitution changes an invariant arginine residue in position B22, which forms a hydrogen bond with the glutamate at A17, stabilizing the insulin molecule. The R55C substitution involves the first of the two arginine residues localized at the site of proteolytic processing between the B-chain and the C-peptide. CONCLUSIONS—Our findings extend the phenotype of INS mutation carriers and suggest that INS screening is warranted not only in neonatal diabetes, but also in MODY and in selected cases of type 1 diabetes.

Exome sequencing reveals FAM20c mutations associated with fibroblast growth factor 23–related hypophosphatemia, dental anomalies, and ectopic calcification

Fibroblast growth factor 23 (FGF23) plays a crucial role in renal phosphate regulation, exemplified by the causal role of PHEX and DMP1 mutations in X‐linked hypophosphatemic rickets and autosomal recessive rickets type 1, respectively. Using whole exome sequencing we identified compound heterozygous mutations in family with sequence similarity 20, member C (FAM20C) in two siblings referred for hypophosphatemia and severe dental demineralization disease. FAM20C mutations were not found in other undiagnosed probands of a national Norwegian population of familial hypophosphatemia. Our results demonstrate that mutations in FAM20C provide a putative new mechanism in human subjects leading to dysregulated FGF23 levels, hypophosphatemia, hyperphosphaturia, dental anomalies, intracerebral calcifications and osteosclerosis of the long bones in the absence of rickets.

Genetic analysis of recently identified type 2 diabetes loci in 1,638 unselected patients with type 2 diabetes and 1,858 control participants from a Norwegian population-based cohort (the HUNT study)

Aims/hypothesisRecent genome-wide association studies performed in selected patients and control participants have provided strong support for several new type 2 diabetes susceptibility loci. To get a better estimation of the true risk conferred by these novel loci, we tested a completely unselected population of type 2 diabetes patients from a Norwegian health survey (the HUNT study).MethodsWe genotyped single nucleotide polymorphisms (SNPs) in PKN2, IGFBP2, FLJ39370 (also known as C4ORF32), CDKAL1, SLC30A8, CDKN2B, HHEX and FTO using a Norwegian population-based sample of 1,638 patients with type 2 diabetes and 1,858 non-diabetic control participants (the HUNT Study), for all of whom data on BMI, WHR, cholesterol and triacylglycerol levels were available. We used diabetes, measures of obesity and lipid values as phenotypes in case-control and quantitative association study designs.ResultsWe replicated the association with type 2 diabetes for rs10811661 in the vicinity of CDKN2B (OR 1.20, 95% CI: 1.06–1.37, p = 0.004), rs9939609 in FTO (OR 1.14, 95% CI: 1.04–1.25, p = 0.006) and rs13266634 in SLC30A8 (OR 1.20, 95% CI: 1.09–1.33, p = 3.9 × 10−4). We found borderline significant association for the IGFBP2 SNP rs4402960 (OR 1.10, 95% CI: 0.99–1.22). Results for the HHEX SNP (rs1111875) and the CDKAL1 SNP (rs7756992) were non-significant, but the magnitude of effect was similar to previous estimates. We found no support for an association with the less consistently replicated FLJ39370 or PKN2 SNPs. In agreement with previous studies, FTO was most strongly associated with BMI (p = 8.4 × 10−4).Conclusions/interpretationOur data show that SNPs near IGFBP2, CDKAL1, SLC30A8, CDKN2B, HHEX and FTO are also associated with diabetes in non-selected patients with type 2 diabetes.

Lack of pancreatic body and tail in HNF1B mutation carriers.

Aims  Hepatocyte nuclear factor 1B (HNF1B) gene mutation carriers have a systemic disease characterized by congenital malformations in the urogenital tract, diabetes mellitus of maturity‐onset diabetes of the young type and dysfunction of the liver and exocrine pancreas. We aimed to investigate pancreatic structure and exocrine function in carriers of HNF1B mutations.

Pancreatic Lipomatosis Is a Structural Marker in Nondiabetic Children With Mutations in Carboxyl-Ester Lipase

Both pancreatic volume reduction and lipomatosis have been observed in subjects with diabetes. The underlying molecular and pathological mechanisms are, however, poorly known, and it has been speculated that both features are secondary to diabetes. We have recently described pancreatic atrophy and lipomatosis in diabetic subjects of two Norwegian families with a novel syndrome of diabetes and exocrine pancreatic dysfunction caused by heterozygous carboxyl-ester lipase (CEL) mutations. To explore the early pathological events in this syndrome, we performed radiological examinations of the pancreas in nondiabetic mutation carriers with signs of exocrine dysfunction. In a case series study at a tertiary hospital, we evaluated 11 nondiabetic and mutation-positive children with fecal elastase deficiency and 11 age- and sex-matched control subjects using ultrasound and magnetic resonance imaging (MRI) to estimate pancreatic fat content. The pancreata of nondiabetic mutation carriers exhibited increased reflectivity on ultrasound and had MRI findings indicative of lipomatosis. Apparently, carriers of heterozygous CEL mutations accumulate fat in their pancreas before the anticipated development of diabetes. Our findings suggest that lipomatosis of the pancreas reflects early events involved in the pathogenesis of diabetes and exocrine pancreatic dysfunction syndrome.

Derivation of Human Induced Pluripotent Stem Cells from Patients with Maturity Onset Diabetes of the Young

Background: Human induced pluripotent stem cells (hiPSCs) can be harnessed for development of novel therapeutics for metabolic disorders. Results: Karyotypically normal hiPSCs were derived from patients with MODY1, MODY2, MODY3, MODY5, or MODY8. Conclusion: hiPSCs were successfully derived from a variety of MODY patients. Significance: MODY-hiPSCs can be used to explore the role of MODY genes in the development and function of pancreatic islet cells. Maturity onset diabetes of the young (MODY) is an autosomal dominant disease. Despite extensive research, the mechanism by which a mutant MODY gene results in monogenic diabetes is not yet clear due to the inaccessibility of patient samples. Induced pluripotency and directed differentiation toward the pancreatic lineage are now viable and attractive methods to uncover the molecular mechanisms underlying MODY. Here we report, for the first time, the derivation of human induced pluripotent stem cells (hiPSCs) from patients with five types of MODY: MODY1 (HNF4A), MODY2 (GCK), MODY3 (HNF1A), MODY5 (HNF1B), and MODY8 (CEL) with a polycistronic lentiviral vector expressing a Cre-excisable human “stem cell cassette” containing the four reprogramming factors OCT4, KLF4, SOX2, and CMYC. These MODY-hiPSCs morphologically resemble human pluripotent stem cells (hPSCs), express pluripotency markers OCT4, SOX2, NANOG, SSEA-4, and TRA-1–60, give rise to derivatives of the three germ layers in a teratoma assay, and are karyotypically normal. Overall, our MODY-hiPSCs serve as invaluable tools to dissect the role of MODY genes in the development of pancreas and islet cells and to evaluate their significance in regulating beta cell function. This knowledge will aid future attempts aimed at deriving functional mature beta cells from hPSCs.

Prevalence of HNF1A (MODY3) mutations in a Norwegian population (the HUNT2 Study).

Aims  Previous reports have indicated that maturity‐onset diabetes of the young (MODY) caused by hepatocyte nuclear factor 1A (HNF1A) mutations (MODY3) is the most common MODY subtype in Northern Europe, but population‐based prevalence estimates are lacking. We sought to determine the prevalence of HNF1A‐MODY in diabetic subjects of a defined Norwegian population (the HUNT2 Study).

Diabetes and Pancreatic Exocrine Dysfunction Due to Mutations in the Carboxyl Ester Lipase Gene-Maturity Onset Diabetes of the Young (CEL-MODY) A PROTEIN MISFOLDING DISEASE

CEL-maturity onset diabetes of the young (MODY), diabetes with pancreatic lipomatosis and exocrine dysfunction, is due to dominant frameshift mutations in the acinar cell carboxyl ester lipase gene (CEL). As Cel knock-out mice do not express the phenotype and the mutant protein has an altered and intrinsically disordered tandem repeat domain, we hypothesized that the disease mechanism might involve a negative effect of the mutant protein. In silico analysis showed that the pI of the tandem repeat was markedly increased from pH 3.3 in wild-type (WT) to 11.8 in mutant (MUT) human CEL. By stably overexpressing CEL-WT and CEL-MUT in HEK293 cells, we found similar glycosylation, ubiquitination, constitutive secretion, and quality control of the two proteins. The CEL-MUT protein demonstrated, however, a high propensity to form aggregates found intracellularly and extracellularly. Different physicochemical properties of the intrinsically disordered tandem repeat domains of WT and MUT proteins may contribute to different short and long range interactions with the globular core domain and other macromolecules, including cell membranes. Thus, we propose that CEL-MODY is a protein misfolding disease caused by a negative gain-of-function effect of the mutant proteins in pancreatic tissues.

Studies in 3,523 Norwegians and Meta-Analysis in 11,571 Subjects Indicate That Variants in the Hepatocyte Nuclear Factor 4α (HNF4A) P2 Region Are Associated With Type 2 Diabetes in Scandinavians

OBJECTIVE— Recent publications have found an association between common variants near the hepatocyte nuclear factor 4α (HNF4A) P2 promoter and type 2 diabetes in some populations but not in others, and the role for HNF4A in type 2 diabetes has remained unclear. In an attempt to address these inconsistencies, we investigated HNF4A single nucleotide polymorphisms (SNPs) in a large population-based sample and included a meta-analysis of published studies. RESEARCH DESIGN AND METHODS— We genotyped 12 SNPs in the HNF4A region in a Norwegian population–based sample of 1,644 individuals with type 2 diabetes and 1,879 control subjects (the Nord-Trøndelag Health Study [HUNT] 2). We combined our data with all previously published case/control studies and performed a meta-analysis. RESULTS— Consistent with initial studies, we found a trend toward association for the SNPs rs1884613 (odds ratio [OR] 1.17 [95% CI 1.03–1.35]) and rs2144908 (1.21 [1.05–1.38]) in the P2 region and for rs4812831 (1.21 [1.02–1.44]), located 34 kb downstream of the P2 promoter. Meta-analysis, comprising 12,292 type 2 diabetic case and 15,519 control subjects, revealed a nonsignificant OR of 1.05 (95% CI 0.98–1.12) but with significant heterogeneity between the populations. We therefore performed a subanalysis including only the data for subjects from Scandinavia. Among the 4,000 case and 7,571 control Scandinavian subjects, a pooled OR of 1.14 (1.06–1.23), P = 0.0004, was found for the SNP rs1884613. CONCLUSIONS— Our results suggest that variation in the HNF4A region is associated with type 2 diabetes in Scandinavians, highlighting the importance of exploring small genetic effects in large, homogenous populations.