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.

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.

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.

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.

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.

SUMOylation of pancreatic glucokinase regulates its cellular stability and activity

Glucokinase is the predominant hexokinase expressed in hepatocytes and pancreatic β-cells, with a pivotal role in regulating glucose-stimulated insulin secretion, illustrated by glucokinase gene mutations causing monogenic diabetes and congenital hyperinsulinemic hypoglycemia. A complex tissue-specific network of mechanisms regulates this enzyme, and a major unanswered question in glucokinase biology is how post-translational modifications control the function of the enzyme. Here, we show that the pancreatic isoform of human glucokinase is SUMOylated in vitro, using recombinant enzymes, and in insulin-secreting model cells. Three N-terminal lysines unique for the pancreatic isoform (Lys-12/Lys-13 and/or Lys-15) may represent one SUMOylation site, with an additional site (Lys-346) common for the pancreatic and the liver isoform. SUMO-1 and E2 overexpression stabilized preferentially the wild-type human pancreatic enzyme in MIN6 β-cells, and SUMOylation increased the catalytic activity of recombinant human glucokinase in vitro and also of glucokinase in target cells. Small ubiquitin-like modifier conjugation represents a novel form of post-translational modification of the enzyme, and it may have an important regulatory function in pancreatic β-cells.

GCK-MODY diabetes associated with protein misfolding, cellular self-association and degradation

GCK-MODY, dominantly inherited mild fasting hyperglycemia, has been associated with >600 different mutations in the glucokinase (GK)-encoding gene (GCK). When expressed as recombinant pancreatic proteins, some mutations result in enzymes with normal/near-normal catalytic properties. The molecular mechanism(s) of GCK-MODY due to these mutations has remained elusive. Here, we aimed to explore the molecular mechanisms for two such catalytically 'normal' GCK mutations (S263P and G264S) in the F260-L270 loop of GK. When stably overexpressed in HEK293 cells and MIN6 β-cells, the S263P- and G264S-encoded mutations generated misfolded proteins with an increased rate of degradation (S263P>G264S) by the protein quality control machinery, and a propensity to self-associate (G264S>S263P) and form dimers (SDS resistant) and aggregates (partly Triton X-100 insoluble), as determined by pulse-chase experiments and subcellular fractionation. Thus, the GCK-MODY mutations S263P and G264S lead to protein misfolding causing destabilization, cellular dimerization/aggregation and enhanced rate of degradation. In silico predicted conformational changes of the F260-L270 loop structure are considered to mediate the dimerization of both mutant proteins by a domain swapping mechanism. Thus, similar properties may represent the molecular mechanisms for additional unexplained GCK-MODY mutations, and may also contribute to the disease mechanism in other previously characterized GCK-MODY inactivating mutations.

HNF1B mutation in a Turkish child with renal and exocrine pancreas insufficiency, diabetes and liver disease

A small-for-gestational age female infant presented with bilateral hypoplastic kidneys at 3 months of age. She developed chronic renal insufficiency. Insulin-requiring, non-autoimmune diabetes was documented at 6 years of age. She had mild steatosis and iron deposition in the liver, and mal-development of pancreas. Genetic studies revealed a heterozygous mutation (S148L) of the HNF1B gene, compatible with an HNF1B-MODY phenotype (MODY5). This is the first case of HNF1B-MODY reported from Turkey and represents a particularly severe phenotype of the disease.

Familial occurrence of neonatal diabetes with duplications in chromosome 6q24: treatment with sulfonylurea and 40-yr follow-up

We present a Norwegian family, followed since 1967, with a chromosome 6q24 duplication in two siblings with neonatal diabetes, in their non-diabetic father, and in a female (third generation) with adult-onset diabetes. The parents (first generation) were healthy and non-consanguineous. After a miscarriage, the couple had two infants with birth weights of 1780 and 1620 g, respectively, both of whom died on their second day of life. Patient I (male, weight 1840 g at term) had a blood glucose level of 33 mmol/L on day 6. He was treated with insulin for 3 months. In adult life he had permanent diabetes, treated with oral hypoglycemic agents. At 43 yr of age, there were no diabetic late complications. Patient II (female, birth weight 1440 g at term) had an increasing blood glucose of 55 mmol/L on day 13. She received insulin treatment for 12.5 months. Subsequently, she was successfully treated with sulfonylurea (tolbutamide) for 10 yr. At 11 yr of age, insulin was again considered necessary. At 40 yr of age, no diabetic late complications were detected. Patient III had a birth weight of 2630 g at term and no diabetic symptoms as a neonate. She had insulin-requiring diabetes from age 19. We conclude that (i) neonatal diabetes with chromosome 6q24 duplications may become a permanent disease in adult life; (ii) this chromosome anomaly may also be associated with adult-onset diabetes; (iii) sulfonylurea treatment may be attempted, and (iv) late diabetic complications may be absent, even after more than 40 yr.

Binding of ATP at the active site of human pancreatic glucokinase--nucleotide-induced conformational changes with possible implications for its kinetic cooperativity

Glucokinase (GK) is the central player in glucose-stimulated insulin release from pancreatic β-cells, and catalytic activation by α-d-glucose binding has a key regulatory function. Whereas the mechanism of this activation is well understood, on the basis of crystal structures of human GK, there are no similar structural data on ATP binding to the ligand-free enzyme and how it affects its conformation. Here, we report on a conformational change induced by the binding of adenine nucleotides to human pancreatic GK, as determined by intrinsic tryptophan fluorescence, using the catalytically inactive mutant form T228M to correct for the inner filter effect. Adenosine-5′-(β,γ-imido)triphosphate and ATP bind to the wild-type enzyme with apparent [L]_0.5 (ligand concentration at half-maximal effect) values of 0.27 ± 0.02 mm and 0.78 ± 0.14 mm, respectively. The change in protein conformation was further supported by ATP inhibition of the binding of the fluorescent probe 8-anilino-1-naphthalenesulfonate and limited proteolysis by trypsin, and by molecular dynamic simulations. The simulations provide a first insight into the dynamics of the binary complex with ATP, including motion of the flexible surface/active site loop and partial closure of the active site cleft. In the complex, the adenosine moiety is packed between two α-helices and stabilized by hydrogen bonds (with Thr228, Thr332, and Ser336) and hydrophobic interactions (with Val412 and Leu415). Combined with enzyme kinetic analyses, our data indicate that the ATP-induced changes in protein conformation may have implications for the kinetic cooperativity of the enzyme.

[Progress in diabetes genetics]

BACKGROUND

Diabetes is classified as Type 1 diabetes, Type 2 diabetes, gestational diabetes and other types. Our goal was to provide an overview of new genetic knowledge of monogenic and type 2 diabetes.

MATERIAL AND METHOD

The article is based on literature identified through a non-systematic search in PubMed and own experience concerning research in diabetes genetics and treatment of patients with monogenic diabetes.

RESULTS

18 genes have been found for which one single mutation may cause diabetes. The most common causes for such monogenic diabetes are mutations in the genes KCNJ11, ABCC8 and INS when the condition is diagnosed at the age 0 - 6 months, and in the genes HNF1A, GCK, HNF4A and HNF1B when the diagnosis is made later than six months of age. Genetic testing is appropriate in assessment of monogenic diabetes, because antidiabetic tablets rather that insulin injections can be used to treat patients with mutations in certain genes; i.e. KCNJ11, ABCC8, HNF1A and HNF4A. Genome-wide association studies have recently identified about 20 genetic variants that increase the risk of Type 2 diabetes, but which have a low predictive value for development of disease. How these genetic variants can cause Type 2 diabetes has not been assessed and clinical relevance remains to be shown.

INTERPRETATION

So far, genetic findings only affect diagnosis and treatment of monogenic diabetes.

Fear of hypoglycaemia in mothers and fathers of children with Type 1 diabetes is associated with poor glycaemic control and parental emotional distress: a population-based study

AIMS

To analyse, in a population-based study, the association between parental fear of hypoglycaemia and (i) the prevalence of hypoglycaemia and diabetes treatment factors in children with Type 1 diabetes and (ii) emotional distress in mothers and fathers.

METHODS

Mothers (n = 103) and fathers (n = 97) of 115 children with Type 1 diabetes (1-15 years old) participated in the study. In addition to demographic and disease-specific data, the participants completed the Hypoglycaemia Fear Survey-Parent version (HFS-P) (worry and behaviour subscales) and the Hopkins Symptom Checklist-25 items (HSCL-25) to measure emotional distress.

RESULTS

A higher HFS-P worry score was associated with higher glycated haemoglobin (HbA(1c)), a higher frequency (>or= 7) of what parents experienced as problematic hypoglycaemic events during the past year and co-morbid disease in the child. A higher HFS-P behaviour score was associated with children receiving insulin injections compared with using an insulin pump and a higher frequency (>or= 7 per day) of blood glucose measurements. The mothers had higher scores than the fathers in both the worry and behaviour subscales. The mothers' and the fathers' HFS-P worry scores correlated significantly with their HSCL-25 scores.

CONCLUSIONS

The association between a higher level of hypoglycaemic-related fear and parental emotional distress and poorer glycaemic control in the child emphasizes the need for programmes to support and guide parents. The results suggest that future interventions should target both the parents' fear and appropriate ways to prevent hypoglycaemia in children with Type 1 diabetes.

[Molecular genetic diagnostics in syndromes associated with the RAS/MAPK signalling pathway]

BACKGROUND

Mutations in genes of the mitogen-activated protein kinase (MAPK) cascade have recently been shown to cause several syndromes characterized by dysmorphic facial features, growth retardation, cognitive impairment, heart disease and cutaneous abnormalities. This signalling pathway involves RAS and RAF proteins, and is central in the regulation of normal growth and the development of cancer.

MATERIAL AND METHODS

We have studied 23 Norwegian patients for whom there was a clinical suspicion of Costello, Noonan or cardio-facio-cutaneous syndrome. Patients suspected of having Noonan syndrome had previously tested negative for mutations in the tyrosine phosphatase gene PTPN11. The material was examined for mutations in the HRAS, KRAS, RAF1 and BRAF genes. Two patients are described to illustrate diagnostic challenges and the usefulness of genetic testing.

RESULTS

Ten of 23 patients (43 %) had mutations affecting the RAS/MAPK signalling pathway. Mutations in HRAS were most common (five cases), while three patients had mutations in KRAS and two in RAF1. Spontaneous mutations were demonstrated in eight cases. Our data indicate an annual incidence of 1-2 new cases of congenital RAS/RAF mutations in Norway.

INTERPRETATION

Upon clinical suspicion of syndromes of the RAS/MAPK signalling pathway, molecular genetic analyses may be essential for a correct diagnosis. Certain mutations are associated with an increased cancer risk, exemplifying that results of genetic laboratory testing may influence medical management.

De novo HRAS and KRAS mutations in two siblings with short stature and neuro-cardio-facio-cutaneous features

Mutations in genes involved in Ras signalling cause Noonan syndrome and other disorders characterised by growth disturbances and variable neuro-cardio-facio-cutaneous features. We describe two sisters, who presented with dysmorphic features, hypotonia, retarded growth and psychomotor retardation. The patients were initially diagnosed with Costello syndrome, an autosomal recessive inheritance was assumed. Remarkably, however, we identified a germline HRAS mutation (G12A) in one sister and a germline KRAS mutation (F156L) in her sibling. Both mutations had arisen de novo. The F156L mutant K-Ras protein accumulated in the active, guanosine triphosphate-bound conformation and affected downstream signalling. The patient harbouring this mutation was followed for three decades, and her cardiac hypertrophy gradually normalised. However, she developed severe epilepsy with hippocampal sclerosis and atrophy. The occurrence of distinct de novo mutations adds to variable expressivity and gonadal mosaicism as possible explanations of how an autosomal dominant disease may manifest as an apparently recessive condition.

Wolcott-Rallison syndrome with 3-hydroxydicarboxylic aciduria and lethal outcome

Wolcott-Rallison syndrome (WRS) (OMIM 226980) is a rare, autosomal recessive disorder with infancy-onset diabetes mellitus, multiple epiphyseal dysplasia, osteopenia, mental retardation or developmental delay, and hepatic and renal dysfunction as main clinical findings. Patients with WRS have mutations in the EIF2AK3 gene, which encodes the pancreatic eukaryotic translation initiation factor 2-alpha kinase 3. We report a female patient who developed insulin-requiring diabetes at 2.5 months of age. Multiple epiphyseal dysplasia was diagnosed at age 2 years. At age 5.5 years she developed a Reye-like syndrome with hypoketotic hypoglycaemia and renal and hepatic insufficiency and died. A partial autopsy showed fat infiltration in the liver and kidneys. Examination of urine by gas chromatography and mass spectrometry showed large amounts of C(6)-dicarboxylic acid (adipic acid), 3-hydroxy-C(8)-dicarboxylic acid, 3-hydroxy-C(10)-dicarboxylic acid, and 3-hydroxydecenedioic acid. Acetoacetate and 3-hydroxybutyrate were absent. The findings suggested a metabolic block in mitochondrial fatty acid oxidation, but lack of material precluded enzyme analyses. The clinical diagnosis of WRS was suggested in retrospect, and confirmed by sequencing of DNA extracted from stored autopsy material. The patient was compound heterozygous for the novel EIF2AK3 mutations c.1694_1695delAT (Y565X) and c.3044T > C (F1015S). Our data suggest that disruption of the EIF2AK3 gene may lead to defective mitochondrial fatty acid oxidation and hypoglycaemia, thus adding to the heterogeneous phenotype of WRS.

Diagnostic screening of MODY2/GCK mutations in the Norwegian MODY Registry

BACKGROUND

Maturity-onset diabetes of the young, type 2 (MODY2) is caused by mutations in the glucokinase gene (GCK). The aim of our study was to determine the prevalence of GCK mutations in the Norwegian MODY Registry and to delineate the clinical phenotype of identified GCK mutation carriers.

METHODS

We screened 122 probands referred to the MODY Registry for mutations in GCK and studied extended families with MODY2.

RESULTS

We found 2 novel (S76Y and N231S) and 13 previously reported (V62A, G72R, L146R, R191W, A208T, M210K, Y215X, M235T, R275C, E339G, R377C, S453L, and IVS5+1G>C) GCK mutations in 23 probands and in their 33 family members. The prevalence of MODY2 was 12% in the Norwegian MODY Registry. The subjects with GCK mutations had features of mild diabetes. Yet, 15 of 56 MODY2 subjects were treated with oral drugs or insulin. Three subjects had retinopathy and one had macrovascular disease. Also, a limited number of cases had elevated fasting serum triglyceride values. Moreover, two GCK mutation carriers were diagnosed with type 1 diabetes.

CONCLUSIONS

According to our diagnostic screening of GCK in the MODY Registry, MODY2 is less prevalent than MODY3 in Norway but is likely to be underreported. Recognizing MODY2 in diabetic patients is important in order to prevent overtreatment. Finally, our study demonstrates the co-occurrence of MODY2 in families with type 1 or type 2 diabetes.

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).

METHODS

Of the 1972 diabetic HUNT2 subjects, we identified a subgroup of 43 suspected MODY cases based on information on family history, disease onset and anti-glutamic acid decarboxylase autoantibody status. These cases were considered a discovery group for HNF1A mutations and underwent full DNA sequencing. Subsequently, the entire cohort of diabetic HUNT2 subjects was screened for three selected HNF1A mutations. Possible founder effects were examined using the Norwegian MODY Registry.

RESULTS

Three subjects from the discovery group harboured HNF1A mutations. Two subjects had the previously described R229Q mutation, one had a novel S6N alteration, whereas the HNF1A hot-spot mutation P291fsinsC was not identified. Genotyping the cohort of diabetic HUNT2 subjects identified five additional R229Q-positive subjects. Microsatellite analysis performed for all R229Q-positive probands of the Norwegian MODY Registry and those found in the HUNT2 population revealed that 17 of 18 (94%) had genotypes consistent with a common haplotype.

CONCLUSIONS

Clinical MODY criteria were fulfilled in 2.2% of diabetic HUNT2 subjects. The minimum prevalence of HNF1A-MODY among diabetic HUNT2 subjects was 0.4%. Because of founder effects, registry-based prevalence studies probably need to be very large and they should also include prospectively collected phenotypes and extensive mutation screening to establish the true prevalence of MODY.

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.

METHODS

We studied five subjects from two families with the previously reported mutation R137_K161del and the novel mutation F148L in HNF1B. All patients underwent computed tomography (CT) and magnetic resonance cholangiopancreatography (MRCP). We measured faecal elastase and serum vitamins D and E.

RESULTS

One of the mutation carriers reported abdominal symptoms. All five subjects had faecal elastase deficiency, three had vitamin D deficiency and two had vitamin E deficiency. Neither CT nor MRCP depicted tissue corresponding to the pancreatic body and tail in the five mutation carriers, indicating agenesis of the dorsal pancreas. The head of the pancreas was slightly atrophic but had normal X-ray attenuation at CT in all patients.

CONCLUSIONS

Agenesis of the pancreatic body and tail and pancreatic exocrine dysfunction are parts of the phenotype in HNF1B mutation carriers. This strengthens the evidence for a critical role of HNF1B in development and differentiation of at least the dorsal pancreas.

Co-occurrence of vitamin D-dependent rickets type 1 and phenylketonuria

Vitamin D-dependent rickets type 1 (VDDR1) was diagnosed in a 15-month-old girl with well-controlled phenylketonuria (PKU). The patient was homozygous for the PAH mutation L249F. The PAH and CYP27B1 genes are both located on the long arm of chromosome 12 and could possibly have been inherited from a common ancestor. The parents were not aware of any ancestral relationship and the patient was compound heterozygous for two different CYP27B1 mutations (R389H and S416X). Her mutations were shown to originate from each of her four grandparents. In Norway, the co-occurrence of PKU and VDDR1 is expected to occur by chance one to two times per billion births.

CONCLUSION

The extremely rare co-occurrence of VDDR1 and PKU requires careful genetic work-up and close attention to family information, but the combined treatment of the two metabolic disorders may not create special problems.

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 beta-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.

De novo HRAS and KRAS mutations in two siblings with short stature and neuro-cardio-facio-cutaneous features

Mutations in genes involved in Ras signalling cause Noonan syndrome and other disorders characterised by growth disturbances and variable neuro-cardio-facio-cutaneous features. We describe two sisters, 46 and 31 years old, who presented with dysmorphic features, hypotonia, feeding difficulties, retarded growth and psychomotor retardation early in life. The patients were initially diagnosed with Costello syndrome, and autosomal recessive inheritance was assumed. Remarkably, however, we identified a germline HRAS mutation (G12A) in one sister and a germline KRAS mutation (F156L) in her sibling. Both mutations had arisen de novo. The F156L mutant K-Ras protein accumulated in the active, guanosine triphosphate-bound conformation and affected downstream signalling. The patient harbouring this mutation was followed for three decades, and her cardiac hypertrophy gradually normalised. However, she developed severe epilepsy with hippocampal sclerosis and atrophy. The occurrence of distinct de novo mutations adds to variable expressivity and gonadal mosaicism as possible explanations of how an autosomal dominant disease may manifest as an apparently recessive condition.

Studies in 3,523 Norwegians and meta-analysis in 11,571 subjects indicate that variants in the hepatocyte nuclear factor 4 alpha (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 4 alpha (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.

Allosteric Activation of Human Glucokinase by Free Polyubiquitin Chains and Its Ubiquitin-dependent Cotranslational Proteasomal Degradation

Human glucokinase (hGK) is a monomeric enzyme highly regulated in pancreatic beta-cells (isoform 1) and hepatocytes (isoforms 2 and 3). Although certain cellular proteins are known to either stimulate or inhibit its activity, little is known about post-translational modifications of this enzyme and their possible regulatory functions. In this study, we have identified isoforms 1 and 2 of hGK as novel substrates for the ubiquitin-conjugating enzyme system of the rabbit reticulocyte lysate. Both isoforms were polyubiquitinated on at least two lysine residues, and mutation analysis indicated that multiple lysine residues functioned as redundant acceptor sites. Deletion of its C-terminal alpha-helix, as part of a ubiquitin-interacting motif, affected the polyubiquitination at one of the sites and resulted in a completely inactive enzyme. Evidence is presented that poly/multiubiquitination of hGK in vitro serves as a signal for proteasomal degradation of the newly synthesized protein. Moreover, the recombinant hGK was found to interact with and to be allosterically activated up to approximately 1.4-fold by purified free pentaubiquitin chains at approximately 100 nm (with an apparent EC(50) of 93 nm), and possibly also by unidentified polyubiquitinated proteins assigned to their equilibrium binding to the ubiquitin-interacting motif site. The affinity of pentaubiquitin binding to hGK is regulated by the ligand (d-glucose)-dependent conformational state of the site. Both ubiquitination of hGK and its activation by polyubiquitin chains potentially represent physiological regulatory mechanisms for glucokinase-dependent insulin secretion in pancreatic beta-cells.

Spatiotemporal trends and age-period-cohort modeling of the incidence of type 1 diabetes among children aged <15 years in Norway 1973-1982 and 1989-2003

OBJECTIVE

We have investigated age-period-cohort effects and spatial and temporal trends for the incidence of type 1 diabetes among 0- to 14-year-old children in Norway.

RESEARCH DESIGN AND METHODS

We included children with the diagnosis of type 1 diabetes in Norway during 1973-1982 and 1989-2003. We studied age, calendar period, and birth cohort effects using Poisson regression, including Holford's method of parameterization, to model the dependencies between age, period, and cohort effects. To study spatiotemporal clustering of cases, we used spatial scan statistics.

RESULTS

The overall incidence rate for the study population <15 years of age was 22.7 cases per 100,000 (95% CI 22.1-23.4), showing an average annual increase of 1.2% (95% CI 0.7-1.5%) during the study period. One specific area with 30% increased incidence rates was identified in the southern part of Norway during 1976-1980 (P = 0.001). Also, children born during 1964-1966 in a specific region in the southern part of Norway as well as children born during 1987-1989 in a region in northern Norway showed 2.0 and 2.6 times, respectively, higher incidence rates compared with the rest of the country (both P = 0.001).

CONCLUSIONS

The incidence of type 1 diabetes among children increased during the study period. Birth cohort effects were identified using the spatiotemporal scan statistic but not using age, period, and birth cohort modeling. Such effects, within the relatively homogenous Norwegian population, suggest the influence of nongenetic etiological factors.

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.

Management of neonatal and infancy-onset diabetes mellitus

Diabetes mellitus is a rare disorder during the first 2 years of life, amounting to about 3-5% of all cases diagnosed before the fifteenth birthday. However, in spite of low numerical values, this is an important diagnosis, since we are dealing with a vulnerable age group with major and special problems related to diagnosis, treatment and psychosocial follow-up. Efforts should be made to establish a molecular genetic diagnosis as early as possible (e.g. homozygous glucokinase deficiency, defects of the ATP-sensitive potassium channel, chromosome 6 imprinting abnormalities). This is particularly important, since patients with Kir6.2 and SUR1 defects can now be treated with oral sulfonylureas. Major advancements have been obtained and continue to be made with respect to diagnosis and classification. Differentiation between transient and permanent neonatal diabetes can only be done after long-term follow-up. Patients should be scrutinized for comorbidity (e.g. celiac disease, Wolcott-Rallison syndrome). Type 1 diabetes is probably the most prevalent subtype, particularly after the first year of life. Insulin treatment in infancy continues to represent major technical, medical and psychological challenges. Family support is mandatory and close attention should be paid to psychosocial issues.

The impact of continuous subcutaneous insulin infusion on health-related quality of life in children and adolescents with type 1 diabetes

AIM

To study the impact of continuous subcutaneous insulin infusion (CSII) therapy on health-related quality of life in children and adolescents with type 1 diabetes.

METHODS

31 children and adolescents with poorly regulated type 1 diabetes (mean HbA1c 10.4%, SD 1.8), mean age 14.4 (1.5) y (range 9.7-17.1) and mean diabetes duration of 6.8 (3.2) y (range 1.3-14.6) were consecutively assigned to CSII therapy. Data for generic (CHQ-CF87) and diabetes-specific quality of life (DQOL) were obtained before initiating pump therapy and twice during 15 mo of treatment. HbA1c, BMI and episodes of severe hypoglycaemia and ketoacidosis were recorded over 15 mo prior to and 15 mo during pump therapy.

RESULTS

Analysis showed improvements on the family activity scale (p=0.041) and change in health score (p=0.042) (CHQ-CF87). Mean HbA1c decreased from 10.4% (1.8) to 9.0% (0.9) after 3 mo, increasing to 9.6% (1.2) after 15 mo. The number of overweight and obese children increased from 4 and 2 before CSII, to 6 and 3 after 15 mo (IOTF criteria). There was a reduction in severe hypoglycaemia episodes from 43.8 to 5.2 per 100 patient years, but no change in ketoacidosis episodes.

CONCLUSION

The degree of limitation experienced by families due to adolescents' general health and well-being was significantly reduced. Expected improvement in metabolic control and frequency of severe hypoglycaemia was observed.

Switching from insulin to oral sulfonylureas in patients with diabetes due to Kir6.2 mutations

BACKGROUND

Heterozygous activating mutations in KCNJ11, encoding the Kir6.2 subunit of the ATP-sensitive potassium (K(ATP)) channel, cause 30 to 58 percent of cases of diabetes diagnosed in patients under six months of age. Patients present with ketoacidosis or severe hyperglycemia and are treated with insulin. Diabetes results from impaired insulin secretion caused by a failure of the beta-cell K(ATP) channel to close in response to increased intracellular ATP. Sulfonylureas close the K(ATP) channel by an ATP-independent route.

METHODS

We assessed glycemic control in 49 consecutive patients with Kir6.2 mutations who received appropriate doses of sulfonylureas and, in smaller subgroups, investigated the insulin secretory responses to intravenous and oral glucose, a mixed meal, and glucagon. The response of mutant K(ATP) channels to the sulfonylurea tolbutamide was assayed in xenopus oocytes.

RESULTS

A total of 44 patients (90 percent) successfully discontinued insulin after receiving sulfonylureas. The extent of the tolbutamide blockade of K(ATP) channels in vitro reflected the response seen in patients. Glycated hemoglobin levels improved in all patients who switched to sulfonylurea therapy (from 8.1 percent before treatment to 6.4 percent after 12 weeks of treatment, P<0.001). Improved glycemic control was sustained at one year. Sulfonylurea treatment increased insulin secretion, which was more highly stimulated by oral glucose or a mixed meal than by intravenous glucose. Exogenous glucagon increased insulin secretion only in the presence of sulfonylureas.

CONCLUSIONS

Sulfonylurea therapy is safe in the short term for patients with diabetes caused by KCNJ11 mutations and is probably more effective than insulin therapy. This pharmacogenetic response to sulfonylureas may result from the closing of mutant K(ATP) channels, thereby increasing insulin secretion in response to incretins and glucose metabolism. (ClinicalTrials.gov number, NCT00334711 [ClinicalTrials.gov].).

From clinicogenetic studies of maturity-onset diabetes of the young to unraveling complex mechanisms of glucokinase regulation

Glucokinase functions as a glucose sensor in pancreatic beta-cells and regulates hepatic glucose metabolism. A total of 83 probands were referred for a diagnostic screening of mutations in the glucokinase (GCK) gene. We found 11 different mutations (V62A, G72R, L146R, A208T, M210K, Y215X, S263P, E339G, R377C, S453L, and IVS5 + 1G>C) in 14 probands. Functional characterization of recombinant glutathionyl S-transferase-G72R glucokinase showed slightly increased activity, whereas S263P and G264S had near-normal activity. The other point mutations were inactivating. S263P showed marked thermal instability, whereas the stability of G72R and G264S differed only slightly from that of wild type. G72R and M210K did not respond to an allosteric glucokinase activator (GKA) or the hepatic glucokinase regulatory protein (GKRP). Mutation analysis of the role of glycine at position 72 by substituting E, F, K, M, S, or Q showed that G is unique since all these mutants had very low or no activity and were refractory to GKRP and GKA. Structural analysis provided plausible explanations for the drug resistance of G72R and M210K. Our study provides further evidence that protein instability in combination with loss of control by a putative endogenous activator and GKRP could be involved in the development of hyperglycemia in maturity-onset diabetes of the young, type 2. Furthermore, based on data obtained on G264S, we propose that other and still unknown mechanisms participate in the regulation of glucokinase.

A hepatocyte nuclear factor-4 alpha gene (HNF4A) P2 promoter haplotype linked with late-onset diabetes: studies of HNF4A variants in the Norwegian MODY registry

Variants in hepatocyte nuclear factor (HNF)-4alpha cause maturity-onset diabetes of the young, type 1 (MODY1) and may also be risk factors for type 2 diabetes. We sequenced the HNF4A gene of 95 MODY3-negative probands from the Norwegian MODY Registry. We found three novel coding variants in exon 8 of HNF4A: G326R, T339I, and W340X. In intron 7, we noted a single nucleotide polymorphism in the binding site of a previously published primer pair, which in some cases caused allelic drop out when amplifying exon 8. We also detected two novel sequence variants of the P2 promoter region, of which P2 -192C>G showed linkage with diabetes in two families (maximal logarithm of odds score of 3.1 and 0.8, respectively). This variant and a surrounding haplotype restricted by 3.7 Mb was also found in two Danish MODY pedigrees. The age of onset was higher in the P2 -192C>G carriers (median 45 years) compared with that reported for other MODY1 individuals. We could not support a biological role of the P2 promoter variant by in vitro transfection assays. In conclusion, we have identified three novel HNF4A mutations and a 3.7-Mb haplotype, including the HNF4A P2 promoter, which was linked with diabetes.

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.

[Molecular diagnostics in diabetes mellitus]

BACKGROUND

Genetic factors are involved in the development of diabetes. We here evaluate the possibilities for a genetic diagnosis of diabetes.

METHODS

This overview is based on a limited literature search in PubMed as well as our own experience.

RESULTS AND INTERPRETATION

Sequence variations in a number of genes and genomic regions result in an increased risk for development of type 1 and type 2 diabetes. With the exception of the HLA genes and their association with type 1 diabetes, these sequence variations each cause only a modest increase in diabetes risk. In contrast, disease-causing mutations can be identified in six genes associated with maturity-onset diabetes of the young (MODY). In most countries, MODY2 and MODY3 are the most frequent subtypes. Sulphonylurea may be the drug of choice when treating MODY3 because sensitivity for the drug is preserved even after long duration of diabetes. Neonatal diabetes is often caused by mutations in a component (Kir6.2) of the potassium channel of the beta cell. Patients can be managed on oral sulphonylurea with sustained metabolic control rather than on insulin injections.

[Fluid management and the risk of cerebral oedema in children with diabetic ketoacidosis]

BACKGROUND

Cerebral oedema is a rare but life-threatening complication of diabetic ketoacidosis in children.

MATERIAL AND METHODS

This paper presents a case report on an infant with diabetic ketoacidosis and in an extreme hyperosmolar and hypernatremic state. Considerations regarding appropriate fluid management and the osmotic role of serum sodium are discussed. Recommendations for treatment are given based on available guidelines and published evidence.

INTERPRETATION

Intracellular swelling of the brain seems to be caused by water moving along osmotic gradients. In diabetic ketoacidosis, sodium and glucose are the dominant osmotic forces. It is important to understand the relation between serum osmolarity, sodium and glucose, as appropriate fluid treatment might prevent this potentially fatal complication.

Evaluation of a programme of group visits and computer-assisted consultations in the treatment of adolescents with Type 1 diabetes

AIM

To examine the effects of group visits and computer-assisted consultations on quality of life and glycaemic control in adolescents with Type 1 diabetes.

METHODS

A total of 116 adolescents, aged 11-17 years, and their parents were randomly assigned to an intervention (n = 62) or a control group (n = 54). The intervention group was invited to a 15-month programme comprising group visits and computer-assisted consultations. The control group was offered traditional out-patient consultations. Outcomes included changes in HbA(1c) and the adolescents' assessment of generic and disease-specific health-related quality of life measured by the Child Health Questionnaire (CHQ-CF87) and the Diabetes Quality of Life Questionnaire (DQOL), respectively.

RESULTS

One hundred and one adolescents (55/46) agreed to participate, mean age 14.2 years (sd 1.5), mean diabetes duration 6.5 years (sd 3.6, range 1-16 years), mean HbA(1c) 9.3% (sd 1.4, range 6.1-12.8%). Eighty-three (72%) completed the questionnaires at follow-up (intervention/control 45/38). There were significant age by randomization group interactions for diabetes-related impact (P = 0.018), diabetes-related worries (P = 0.004), mental health (P = 0.046) and general behaviour (P = 0.029), implying that the intervention was effective in older adolescents (above 13-14 years). No significant effects on mean HbA(1c) were identified.

CONCLUSIONS

Group visits and computer-assisted consultations had beneficial effects on health-related quality of life in older adolescents, the role of this intervention being questionable in younger adolescents.

Health-related quality of life and metabolic control in adolescents with diabetes: the role of parental care, control, and involvement

This questionnaire-based study explored the role of parenting in health-related quality of life in a population of 115 adolescents with type 1 diabetes (aged 11-18 years, 48% girls). Healthy adolescents (n = 9,345) and physically disabled adolescents (n = 291) were included as controls. The adolescents with diabetes reported their parents as being more controlling and involved than did adolescents in the 2 other groups. In multiple regression analyses, age, gender, and a higher degree of parental care and involvement explained 46% of the variation in mental health. Age, gender, a higher degree of parental care and involvement, and a lower perception of parental control explained 52% of the variation in diabetes life-satisfaction. Neither glycosylated hemoglobin nor the other clinical variables studied were significantly related to the perception of health-related quality of life. Family support should be provided to facilitate coping with everyday management and demands of diabetes.

Diagnostic screening of NEUROD1 (MODY6) in subjects with MODY or gestational diabetes mellitus

AIMS

Diagnostic screening of NEUROD1 in patients with maturity-onset diabetes of the young (MODY) without mutations in the known MODY-genes (MODYX) and in subjects diagnosed with gestational diabetes mellitus.

METHODS

Direct sequencing of NEUROD1 was performed in (i) 73 probands with clinical MODY without mutations in hepatocyte nuclear factor (HNF)-4alpha (MODY1), glucokinase (MODY2) and hepatocyte nuclear factor (HNF)-1alpha (MODY3), and (ii) 51 subjects diagnosed with gestational diabetes. Control material consisted of 105 anonymous blood donors.

RESULTS

Mean age at diagnosis of diabetes was 22 and 30 years in the MODYX patients and gestational diabetes mellitus subjects, respectively. Mean fasting blood glucose (9.6 +/- 4.3 vs. 5.7 +/- 1.0 mml/l) as well as glycosylated haemoglobin (8.2 +/- 2.4 vs. 6.0 +/- 0.6%) were higher in the MODYX patients than subjects with gestational diabetes. NEUROD1 mutations were not detected in our two study groups. Three previously reported polymorphisms were found: Ala45Thr, Pro197His and IVS1 -32 nt C>T. The amino acid substitution serine to cysteine in codon 29 (designated Ser29Cys) was detected in one out of 105 control subjects. As the control material consisted of anonymous blood donors, we were prevented from investigation of possible co-segregation between the sequence variant Ser29Cys and diabetes mellitus.

CONCLUSIONS

As we found no NEUROD1 mutations, diagnostic screening for this gene is not warranted in Norwegian MODYX patients. Our study also suggests that NEUROD1 is not a candidate gene in gestational diabetes mellitus (GDM). The sequence variant Ser29Cys was identified in one anonymous DNA sample, but we were prevented from studying possible co-segregation with diabetes mellitus.

Preserved insulin response to tolbutamide in hepatocyte nuclear factor-1alpha mutation carriers

AIMS

Diabetic subjects with mutations in the gene encoding hepatocyte nuclear factor (HNF)-1alpha (MODY3) are prone to develop hypoglycaemia at low doses of glibenclamide, interpreted as sulphonylurea hypersensitivity. The present study was undertaken to compare the plasma insulin responses to glucose and tolbutamide in HNF-1alpha mutation carriers with those of healthy control subjects.

METHODS

Seven mutation carriers; three normoglycaemic, two with impaired glucose tolerance, and two with newly detected diabetes, underwent an oral glucose tolerance test and a tolbutamide-modified intravenous glucose tolerance test with measurements of plasma insulin. Twenty-two healthy subjects served as controls.

RESULTS

The plasma insulin response to intravenous glucose was reduced in the HNF-1alpha mutation carriers compared to the control subjects, with an area under the curve (median (interquartile range)) of 812 min pmol/l (421, 1647) and 1933 min pmol/l (1521, 2908), respectively (P = 0.03). In striking contrast, the plasma insulin response to tolbutamide was preserved, with an area under the curve of 2109 min pmol/l (1126, 3172) and 2250 min pmol/l (1614, 3276) in the mutation carriers and control subjects, respectively.

CONCLUSIONS

HNF-1alpha mutation carriers are characterized by preserved tolbutamide-induced insulin secretion. Compared to healthy subjects, our MODY3 individuals did not show any increased serum insulin response to tolbutamide, suggesting that HNF-1alpha mutation carriers are not characterized by sulphonylurea hypersensitivity.

[Unexpected and unexplained deaths among young patients with diabetes mellitus]

BACKGROUND

We studied the occurrence of unexpected and unexplained deaths in 0-39 year-old subjects with diabetes.

MATERIAL AND METHODS

Statistics Norway provided information about persons who had died in the 1991-1995 period with a diagnosis of diabetes on their death certificate. Relevant information was obtained from autopsy reports and patients' physicians.

RESULTS

117 deaths from all causes were ascertained. Four patients (3.4%) fulfilled the criteria of "dead in bed" syndrome; three males and one female, age range 21-36 years, duration of diabetes 5-23 years. Severe episodes of hypoglycaemia were reported in three cases. Autopsy, performed in three cases, was negative.

INTERPRETATION

Dead in bed syndrome in young persons with diabetes is a rare, but dramatic condition. The relationship to nocturnal hypoglycaemia remains hypothetical.