Hanna Huopio

Dominantly inherited hyperinsulinism caused by a mutation in the sulfonylurea receptor type 1

ATP-sensitive potassium channels play a major role in linking metabolic signals to the exocytosis of insulin in the pancreatic beta cell. These channels consist of two types of protein subunit: the sulfonylurea receptor SUR1 and the inward rectifying potassium channel Kir6.2. Mutations in the genes encoding these proteins are the most common cause of congenital hyperinsulinism (CHI). Since 1973, we have followed up 38 pediatric CHI patients in Finland. We reported previously that a loss-of-function mutation in SUR1 (V187D) is responsible for CHI of the most severe cases. We have now identified a missense mutation, E1506K, within the second nucleotide binding fold of SUR1, found heterozygous in seven related patients with CHI and in their mothers. All patients have a mild form of CHI that usually can be managed by long-term diazoxide treatment. This clinical finding is in agreement with the results of heterologous coexpression studies of recombinant Kir6.2 and SUR1 carrying the E1506K mutation. Mutant K(ATP) channels were insensitive to metabolic inhibition, but a partial response to diazoxide was retained. Five of the six mothers, two of whom suffered from hypoglycemia in infancy, have developed gestational or permanent diabetes. Linkage and haplotype analysis supported a dominant pattern of inheritance in a large pedigree. In conclusion, we describe the first dominantly inherited SUR1 mutation that causes CHI in early life and predisposes to later insulin deficiency.

A new subtype of autosomal dominant diabetes attributable to a mutation in the gene for sulfonylurea receptor 1

BACKGROUND ATP-sensitive potassium (KATP) channels are major regulators of glucose-induced insulin secretion in pancreatic beta cells. We have described a dominant heterozygous mutation--E1506K--in the sulfonylurea receptor 1 (SUR1) gene (ABCC8) in a Finnish family, which leads to congenital hyperinsulinaemia due to reduction of K(ATP)-channel activity. We aimed to characterise glucose metabolism in adults heterozygous for the E1506K mutation. METHODS Glucose tolerance was assessed by an oral glucose tolerance test, insulin secretion by the intravenous glucose tolerance test and hyperglycaemic clamp, and insulin sensitivity by hyperinsulinaemic euglycaemic clamp in 11 people heterozygous for the E1506K mutation and 19 controls. FINDINGS Four people who were heterozygous for the SUR1 E1506K mutation had diabetes, five had impaired glucose tolerance, one had impaired fasting glucose, and one had normal glucose tolerance. Although glucose-induced, first-phase insulin secretion was normal in children younger than 10 years of age who were heterozygous for the SUR1 E1506K mutation (n=2; 66 and 334 pmol/L), it fell rapidly after puberty (n=3; 12-32 pmol/L), and was almost completely lost in adulthood (n=11; 12-32 pmol/L). Furthermore, these heterozygous people had a substantial reduction in maximum glucose-stimulated insulin secretion during hyperglycemic clamp (carriers without diabetes 422 pmol/L; carriers with diabetes 97 pmol/L). By contrast, insulin sensitivity (M/I value) was normal in carriers of the E1506K mutation who did not have diabetes and was reduced by 15% in those who were heterozygous with diabetes (0.07 in those without diabetes and 0.05 in those with the disorder; not significantly different from controls). INTERPRETATION Heterozygous E1506K substitution in the SUR1 gene causes congenital hyperinsulinism in infancy, loss of insulin secretory capacity in early adulthood, and diabetes in middle-age. This variant represents a new subtype of autosomal dominant diabetes.

Association of risk variants for type 2 diabetes and hyperglycemia with gestational diabetes

OBJECTIVE The aim of this study was to investigate the association of risk variants for type 2 diabetes (T2D) and hyperglycemia with gestational diabetes (GDM). DESIGN AND METHODS Five hundred and thirty-three Finnish women who were diagnosed with GDM and 407 controls with normal glucose tolerance during the pregnancy were genotyped for 69 single-nucleotide polymorphisms (SNPs) which have been previously verified as susceptibility risk variants for T2D and hyperglycemia. All participants underwent an oral glucose tolerance test at the follow-up study after the index pregnancy. RESULTS Risk variants rs10830963 and rs1387153 of MTNR1B were significantly associated with GDM (odds ratio (OR)=1.62 (95% CI 1.34-1.96), P=4.5 × 10⁻⁷ and 1.38 (1.14-1.66), P=7.6 × 10⁻⁴ respectively). Both SNPs of MTNR1B were also significantly associated with elevated fasting glucose level and reduced insulin secretion at follow-up. Additionally, risk variants rs9939609 of FTO, rs2796441 of TLE1, rs560887 of G6PC2, rs780094 of GCKR, rs7903146 of TCF7L2 and rs11708067 of ADCY5 showed nominally significant associations with GDM (OR range from 1.25 to 1.30). CONCLUSIONS Our study suggests that GDM and T2D share a similar genetic background. Our findings also provide further evidence that risk variants of MTNR1B are associated with GDM by increasing fasting plasma glucose and decreasing insulin secretion.

Autosomal Dominant Diabetes Arising from a Wolfram Syndrome 1 Mutation

We used an unbiased genome-wide approach to identify exonic variants segregating with diabetes in a multigenerational Finnish family. At least eight members of this family presented with diabetes with age of diagnosis ranging from 18 to 51 years and a pattern suggesting autosomal dominant inheritance. We sequenced the exomes of four affected members of this family and performed follow-up genotyping of additional affected and unaffected family members. We uncovered a novel nonsynonymous variant (p.Trp314Arg) in the Wolfram syndrome 1 (WFS1) gene that segregates completely with the diabetic phenotype. Multipoint parametric linkage analysis with 13 members of this family identified a single linkage signal with maximum logarithm of odds score 3.01 at 4p16.2-p16.1, corresponding to a region harboring the WFS1 locus. Functional studies demonstrate a role for this variant in endoplasmic reticulum stress, which is consistent with the β-cell failure phenotype seen in mutation carriers. This represents the first compelling report of a mutation in WFS1 associated with dominantly inherited nonsyndromic adult-onset diabetes.

Effects of euglycaemic and hypoglycaemic hyperinsulinaemia on sympathetic and parasympathetic regulation of haemodynamics in healthy subjects.

The effects of hypoglycaemia during hyperinsulinaemia, occurring under various pathophysiological conditions, on the cardiovascular regulatory system and vasculature are largely unknown. The aim of the present study was to investigate regulatory and haemodynamic responses to acute hyperinsulinaemia and consequent hypoglycaemia in 18 healthy subjects. Blood sampling and 5 min ECG and blood pressure recordings were performed at baseline and during the euglycaemic and hypoglycaemic phases of a hyperinsulinaemic clamp. Heart rate variability (HRV) and blood pressure variability (BPV) were assessed by using power spectral analysis, and baroreflex sensitivity (BRS) was assessed using the cross-spectral method. Stroke volume was assessed from the non-invasive blood pressure signal by the arterial pulse contour method. Euglycaemic hyperinsulinaemia did not change plasma catecholamine concentrations, HRV, BPV, BRS, heart rate, blood pressure, stroke volume, cardiac output or peripheral resistance. However, hyperinsulinaemic hypoglycaemia resulted in an 11.7-fold increase in the plasma adrenaline concentration (from 0.19+/-0.03 to 1.68+/-0.32 nmol/l; P <0.001), and a modest 1.3-fold increase in the plasma noradrenaline concentration (from 1.74+/-0.22 to 2.02+/-0.19 nmol/l; P <0.05) compared with baseline. Furthermore, we observed significant decreases in diastolic blood pressure (from 68+/-3 to 60+/-3 mmHg; P <0.05) and peripheral resistance (from 24.1+/-1.2 to 18.5+/-1.1 mmHg.min(-1) x l(-1); P <0.01). Stroke volume and cardiac output increased markedly from the euglycaemic to the hypoglycaemic period only ( P <0.01 for both). Hypoglycaemia did not influence HRV, BPV or BRS. Our findings indicate that hyperinsulinaemic hypoglycaemia is characterized by a significant increase in the plasma adrenaline concentration and by decreases in peripheral resistance and blood pressure. Counter-regulation during hyperinsulinaemic hypoglycaemia involves selective adrenomedullary sympathetic activation, and does not influence cardiac parasympathetic regulation or baroreflex control of heart rate.

A Mouse Model of Human Hyperinsulinism Produced by the E1506K Mutation in the Sulphonylurea Receptor SUR1

Loss-of-function mutations in the KATP channel genes KCNJ11 and ABCC8 cause neonatal hyperinsulinism in humans. Dominantly inherited mutations cause less severe disease, which may progress to glucose intolerance and diabetes in later life (e.g., SUR1-E1506K). We generated a mouse expressing SUR1-E1506K in place of SUR1. KATP channel inhibition by MgATP was enhanced in both homozygous (homE1506K) and heterozygous (hetE1506K) mutant mice, due to impaired channel activation by MgADP. As a consequence, mutant β-cells showed less on-cell KATP channel activity and fired action potentials in glucose-free solution. HomE1506K mice exhibited enhanced insulin secretion and lower fasting blood glucose within 8 weeks of birth, but reduced insulin secretion and impaired glucose tolerance at 6 months of age. These changes correlated with a lower insulin content; unlike wild-type or hetE1506K mice, insulin content did not increase with age in homE1506K mice. There was no difference in the number and size of islets or β-cells in the three types of mice, or evidence of β-cell proliferation. We conclude that the gradual development of glucose intolerance in patients with the SUR1-E1506K mutation might, as in the mouse model, result from impaired insulin secretion due a failure of insulin content to increase with age.

Does gestational diabetes affect women's health-related quality of life after delivery?

OBJECTIVES Our objective in this study was to investigate the effects of gestational diabetes (GDM) on womens health-related quality of life (HRQoL) after delivery. This study investigates the differences between a GDM group and a control group. STUDY DESIGN Using random sampling, 100 women who had had GDM were selected from a birth register. Glucose tolerance tests administered to these participants during pregnancy had yielded 1 or 2 abnormal values. The control group (n=100) consisted of women who had normal glucose tolerance test during pregnancy. The informants were invited to a personal meeting, where their weight and height were measured and where they also answered the 15D questionnaire. Data were analysed with chi(2) - test, Mann-Whitney-test, independent samples t-test and regression analysis. RESULTS The results for investigating the HRQoL indicated no significant differences on the 15D dimensions between the GDM group and the control group. The HRQoL for both groups was weakest on the dimensions of sleeping, discomfort and symptoms. Furthermore, the control group had a lower vitality score than the GDM group did. Analysis of the influence of background factors on HRQoL showed that women in a relationship experienced higher quality of life than single women. CONCLUSION This study showed no indication that womens lowered HRQoL, as measured by the 15D instrument, could be partly explained by GDM. Womens HRQoL was insignificantly decreased on the dimension of vitality only, so finding motivation for lifestyle changes and diabetes self-care may become challenging.

Growth and Cardiovascular Risk Factors in Prepubertal Children Born Large or Small for Gestational Age

Background: Both large and small birth sizes are associated with an increased risk of developing cardiovascular and metabolic problems later in life. We studied whether such associations can be observed at prepubertal age. Methods: A cohort of 49 large (LGA), 56 appropriate (AGA), and 23 small for gestational age (SGA)-born children (age range 5-8 years) were studied. Being born SGA, AGA, or LGA was the exposure, and being overweight at prepubertal age was the main outcome. Blood pressure measurements, laboratory parameters, and whole-body dual-energy X-ray absorptiometry were secondary outcomes. Results: The LGA-born children were significantly taller than the AGA controls (p = 0.03), and the SGA children were lighter and shorter compared to the AGA (p = 0.002 and 0.001) and LGA children (p < 0.001). The mean plasma glucose was higher in the LGA than in the SGA group (p = 0.006). Being born LGA (OR 3.82) and the ponderal index Z-score at birth (OR 4.24) were strong predictors for being overweight or obese in childhood. Conclusion: The children born LGA remained taller and heavier than those born AGA or SGA in mid-childhood, and they had a higher body mass index and body fat percentage than the SGA-born children. The differences in other cardiometabolic risk factors were minimal between the birth size groups.

The risk of metabolic syndrome in women with previous GDM in a long-term follow-up

Abstract The aim of this study was to evaluate the incidence of metabolic syndrome (MetS) during long-term follow-up of women with gestational diabetes (GDM). Furthermore, we evaluated the glycemic measures from an oral glucose tolerance test (OGTT) during pregnancy as predictors of incident MetS. Women diagnosed with GDM were divided into two groups according to the results of OGTT: one abnormal value = GDM1 (n = 338) and two abnormal values = GDM2 (n = 151), while women with normal glucose tolerance (n = 385) served as controls. MetS and its components were evaluated in a follow-up study (mean follow-up time 7.3 ± 5.1 years) according to the International Diabetes Federation (IDF) criteria. Fasting plasma glucose in OGTT was the best predictor of incident MetS in ROC (area under the curve) analysis. The incidence of MetS during a <5-year follow-up was 22.2% in controls, 39.3% in GDM1 and 60.4% in GDM2; and >10-year follow-up 24.2%, 46.2% and 62.5%, respectively. In controls and GDM2, the incidence of MetS remained nearly constant during the follow-up, whereas in GDM1 it increased. In conclusion, already mild gestational glucose intolerance may progress to MetS and therefore merits intervention measures to prevent future cardiovascular disease.

Post-challenge glycemia during pregnancy as a marker of future risk of type 2 diabetes: a prospective cohort study

Abstract The aim of this study was to evaluate the glycemic measures from an oral glucose tolerance test (OGTT) during pregnancy as predictors of incident type 2 diabetes mellitus (T2DM). Patients diagnosed with gestational diabetes mellitus (GDM) were divided into two groups according to the results of OGTT: one abnormal value = GDM1 (n = 338) and two abnormal values = GDM2 (n = 151), while women with normal glucose tolerance served as controls (n = 385). Glucose tolerance was re-evaluated with an OGTT in a follow-up study (average follow-up time 7.3 ± 5.1 years). The incidence of T2DM after 10 years follow-up increased progressively by the degree of the glycemic abnormality during pregnancy: 0.8% in controls, 3.8% in GDM1 (adjusted HR 17.6, 95% CI 1.9–162.3) and 25.0% in GDM2 (adjusted HR 72.9, 95% CI 9.6–553.7), respectively (p = <0.0001). The risk of T2DM is significantly increased in women with two or more abnormal values in OGTT during pregnancy. Post-challenge glucose levels in OGTT were the best predictors of the incident T2DM in ROC analysis and they therefore identify the greatest risk group for targeted prevention of T2DM after GDM.