Sensitivity to sulphonylureas in patients with hepatocyte nuclear factor-1alpha gene mutations: evidence for pharmacogenetics in diabetes

Acquired non-type 1 diabetes in childhood: subtypes, diagnosis, and management

Over the past 30 years it has become apparent that not all diabetes presenting in childhood is autoimmune type 1. Increasingly type 2 diabetes, maturity onset diabetes of the young, iatrogenic diabetes, and rare syndromic forms of diabetes such as Wolfram's syndrome have been identified in children. This review is aimed at the general paediatrician looking after children with diabetes, and aims to provide an algorithm for assessment, investigation, and suggested management for the newly diagnosed child with suspected non-type 1 diabetes. This article will also be relevant to the child with atypical diabetes-that is, on low insulin doses outside the honeymoon period.

First UK survey of paediatric type 2 diabetes and MODY

AIMS

To estimate the UK prevalence of childhood type 2 diabetes and maturity onset diabetes of the young (MODY), and distinguish them from each other and from type 1 diabetes.

METHODS

The British Society for Paediatric Endocrinology and Diabetes Clinical Trials/Audit Group undertook a cross-sectional questionnaire survey of all paediatric diabetes centres during 2000, collecting data on all children with non-type 1 diabetes.

RESULTS

Of 112 children reported to the survey, 25 had type 2 diabetes and 20 had MODY. In contrast to type 1, type 2 patients presented later (12.8 v 9.3 years), were usually female, overweight, or obese (92% v 28%), and a greater proportion were of ethnic minority origin (56% v 22%). In contrast to type 2, MODY patients were younger (10.8 years), less likely to be overweight or obese (50% v 92%), and none were from ethnic minority groups. The crude minimum UK prevalence of type 2 diabetes under 16 years is 0.21/100 000, and of MODY is 0.17/100 000. South Asian children have a relative risk of type 2 diabetes of 13.7 compared to white UK children.

CONCLUSIONS

UK children still have a low prevalence of type 2 diabetes. Children from ethnic minorities are at significantly higher risk, but in white UK children with non-type 1 diabetes a diagnosis of MODY is as likely as type 2 diabetes. Childhood type 2 diabetes is characterised by insulin resistance, and is distinct from both type 1 and MODY.

Hepatic expression of cytochrome P450s in hepatocyte nuclear factor 1-alpha (HNF1alpha)-deficient mice

Hepatocyte nuclear factor 1 alpha (HNF1alpha) is a liver enriched homeodomain-containing transcription factor that has been shown to transactivate the promoters of several cytochrome P450 (CYP) genes, including CYP2E1, CYP1A2, CYP7A1, and CYP27, in vitro. In humans, mutations in HNF1alpha are linked to the occurrence of maturity onset diabetes of the young type 3, an autosomal dominant form of non-insulin-dependent diabetes mellitus in which afflicted subjects generally develop hyperglycemia before 25 years of age. Mice lacking HNF1alpha also develop similar phenotypes reminiscent of non-insulin-dependent diabetes mellitus. To investigate a potential role for HNF1alpha in the regulation of CYPs in vivo, the expression of major CYP genes from each family was examined in the livers of mice lacking HNF1alpha. Analysis of CYP gene expression revealed marked reductions in expression of Cyp1a2, Cyp2c29 and Cyp2e1, and a moderate reduction of Cyp3a11. In contrast Cyp2a5, Cyp2b10 and Cyp2d9 expression were elevated. There are also significant changes in the expression of genes encoding CYPs involved in fatty acid and bile acid metabolism characterized by a reduction in the expression of Cyp7b1, and Cyp27 as well as elevations in Cyp4a1/3, Cyp7a1, Cyp8b1, and Cyp39a1 expression. These results point to a critical role for HNF1alpha in the regulation of CYPs in vivo and suggest that this transcription factor may have an important influence on drug metabolism as well as lipid and bile acid homeostasis in maturity onset diabetes of the young type 3 diabetics.

Genetic cause of hyperglycaemia and response to treatment in diabetes

BACKGROUND

Type 2 diabetes shows evidence of underlying heterogeneity. No studies have assessed whether different causes for diabetes change the response to oral hypoglycaemic therapy. In a few cases, patients with diabetes caused by mutations in the hepatocyte nuclear factor 1alpha (HNF-1alpha) gene have been described as sensitive to the hypoglycaemic effects of sulphonylureas. We aimed to see whether the glycaemic response to the sulphonylurea gliclazide and the biguanide metformin differed in HNF-1alpha diabetes and type 2 diabetes, and to investigate the mechanism for differences in sulphonylurea sensitivity.

METHODS

We did a randomised crossover trial of glicazide and metformin in 36 patients, either with diabetes caused by HNF-1alpha mutations or type 2 diabetes, who were matched for body-mass index and fasting plasma glucose. The primary outcome was reduction in fasting plasma glucose. Analysis was by intention to treat. We assessed possible mechanisms for sulphonylurea sensitivity through insulin sensitivity, insulin secretory response to glucose and tolbutamide, and tolbutamide clearance.

FINDINGS

Patients with HNF-1alpha diabetes had a 5.2-fold greater response to gliclazide than to metformin (fasting plasma glucose reduction 4.7 vs 0.9 mmol/L, p=0.0007) and 3.9-fold greater response to gliclazide than those with type 2 diabetes (p=0.002). Patients with HNF-1alpha diabetes had a strong insulin secretory response to intravenous tolbutamide despite a small response to intravenous glucose, and were more insulin sensitive than those with type 2 diabetes. Sulphonylurea metabolism was similar in both patient groups.

INTERPRETATION

The cause of hyperglycaemia changes the response to hypoglycaemic drugs; HNF-1alpha diabetes has marked sulphonylurea sensitivity. This pharmacogenetic effect is consistent with models of HNF-1alpha deficiency, which show that the beta-cell defect is upstream of the sulphonylurea receptor. Definition of the genetic basis of hyperglycaemia has implications for patient management.

Response to treatment with rosiglitazone in familial partial lipodystrophy due to a mutation in the LMNA gene

BACKGROUND

Familial partial lipodystrophy (FPLD) is a monogenic form of diabetes characterised by a dominantly inherited disorder of adipose tissue associated with the loss of subcutaneous fat from the limbs and trunk, with excess fat deposited around the face and neck. The lipodystrophy causes severe insulin resistance, resulting in acanthosis nigricans, diabetes, dyslipidaemia, and increased risk of cardiovascular disease. Preliminary results from animals and man suggest that increasing subcutaneous fat by treatment with thiazolidinediones should improve insulin resistance and the associated features of this syndrome.

CASE REPORT

We report a 24-year-old patient with FPLD caused by a mutation in the LMNA gene (R482W) treated with 12 months of rosiglitazone. Subcutaneous fat increased following rosiglitazone treatment as demonstrated by a 29% generalised increase in skin-fold thickness. Leptin levels increased from 5.8 to 11.2 ng/ml. Compared with treatment on Metformin, there was an increase in insulin sensitivity (HOMA S% 17.2-31.6) but no change in glycaemic control. The lipid profile worsened during the follow-up period.

CONCLUSION

This initial case suggests that, for modification of cardiovascular risk factors, there are no clear advantages in treating patients with FPLD with rosiglitazone despite increases in subcutaneous adipose tissue. Larger series will be needed to identify moderate beneficial effects and treatment may be more effective in patients with generalised forms of lipodystrophy.

Etiological investigation of diabetes in young adults presenting with apparent type 2 diabetes

OBJECTIVE

Young adults with newly diagnosed apparent type 2 diabetes present the clinician with a wide differential diagnosis of possible etiology, including autoimmune and genetic causes as well as young-onset type 2 diabetes (YT2D). The characteristics of these groups have been described, but it is not known in which subjects investigation for etiology may be beneficial.

RESEARCH DESIGN AND METHODS

A total of 268 unselected U.K. Caucasian subjects diagnosed at ages 18-45 years and not treated with permanent insulin for < or =6 months were studied. All subjects underwent clinical assessment and screening for GAD antibodies (GADA) and tyrosine phosphatase IA-2 antibodies (IA-2A). Screening for a common mutation in the hepatocyte nuclear factor-1 alpha (HNF-1 alpha) gene and the common mitochondrial mutation was performed in the antibody-negative subjects. Subjects without insulin resistance were selected for sequencing of the HNF-1 alpha gene.

RESULTS

A specific etiology was defined in 11.6% of the 268 subjects and in 24.7% of the lean subjects. Twenty-six subjects (9.7%) were positive for a beta-cell antibody, one subject had familial partial lipodystrophy and the lamin A/C mutation R482W, and two subjects had the mitochondrial mutation A3243G. Two of 15 selected subjects had HNF-1 alpha mutations, the novel missense mutation A501T, and the previously reported R583Q.

CONCLUSIONS

This unselected series shows that there is considerable heterogeneity in apparent YT2D. beta-Cell autoantibodies should be performed in all those presenting at ages 18-45 years. Genetic investigations can be targeted to phenotypically defined subjects. The finding of a specific etiology will allow individualization of management and give patients valuable information about their condition.

The search for type 2 diabetes genes

Type 2 diabetes (T2DM) is a serious disease with severe complications. Around one in 10 people alive today suffer from type 2 diabetes or are destined to develop it before they die. Inheritance plays an important role in the cause of type 2 diabetes. A considerable amount of research is devoted to defining the genes involved in the aetiology of this widespread disease. This information is crucial if we are to improve our methods of preventing and treating diabetes. Over the last 25 years there have been considerable advances in our understanding of the genetics of diabetes. Important discoveries have been made in dissecting the genes involved in rare monogenic forms of type 2 diabetes which has become a paradigm for genetic studies of type 2 diabetes. This review focuses on the main approaches currently adopted and our current understanding of the genes involved in susceptibility to type 2 diabetes.

Regulation of P450 genes by liver-enriched transcription factors and nuclear receptors

Cytochrome P450s (P450s) constitute a superfamily of heme-proteins that play an important role in the activation of chemical carcinogens, detoxification of numerous xenobiotics as well as in the oxidative metabolism of endogenous compounds such as steroids, fatty acids, prostaglandins, and leukotrienes. In addition, some P450s have important roles in physiological processes, such as steroidogenesis and the maintenance of bile acid and cholesterol homeostasis. Given their importance, the molecular mechanisms of P450 gene regulation have been intensely studied. Direct interactions between transcription factors, including nuclear receptors, with the promoters of P450 genes represent one of the primary means by which the expression of these genes is controlled. In this review, several liver-enriched transcription factors that play a role in the tissue-specific, developmental, and temporal regulation of P450s are discussed. In addition, the nuclear receptors that play a role in the fine control of cholesterol and bile acid homeostasis, in part, through their modulation of specific P450s, are discussed.

Identifying hepatic nuclear factor 1alpha mutations in children and young adults with a clinical diagnosis of type 1 diabetes

OBJECTIVE

HNF-1alpha gene mutations (MODY3) present with marked hyperglycemia in lean young adults and may, therefore, be mistaken for type 1 diabetes, with implications for individual treatment and risk of diabetes in other family members. We examined the prevalence of HNF-1alpha mutations in families with three generations of diabetes identified in a population-based study of childhood diabetes, representing a subpopulation in which misclassification was likely.

RESEARCH DESIGN AND METHODS

In a study population of 1,470 families, 36 families (2.4%) with three affected generations were identified. In the 18 families in whom DNA samples were available, islet autoantibody testing, HLA class II genotyping, and HNF-1alpha sequencing were performed.

RESULTS

At least one islet autoantibody was found in 13 of 14 probands, and diabetes-associated HLA class II haplotypes were found in 17 of 18. One proband, who had no islet autoantibodies and was homozygous for the protective HLA haplotype DRB1*02-DQB1*0602, had a novel HNF-1alpha heterozygous nonsense mutation (R54X). This mutation cosegregated with diabetes in the family. The proband, his brother, mother, and maternal grandmother were diagnosed with type 1 diabetes aged 14-18 years and treated with insulin (0.39-0.74 units/kg) from diagnosis. The mother has since been successfully transferred to sulfonylurea treatment.

CONCLUSIONS

Family history alone is of limited value in identification of individuals with HNF-1alpha mutations, and we propose a stepwise approach that restricts sequencing of the HNF-1alpha gene to those with a family history of diabetes who also test negative for islet autoantibodies.

Decreased glibenclamide uptake in hepatocytes of hepatocyte nuclear factor-1alpha-deficient mice: a mechanism for hypersensitivity to sulfonylurea therapy in patients with maturity-onset diabetes of the young, type 3 (MODY3)

Diabetes in subjects with hepatocyte nuclear factor (HNF)-1alpha gene mutations (maturity-onset diabetes of the young [MODY]-3) is characterized by impaired insulin secretion. Surprisingly, MODY3 patients exhibit hypersensitivity to the hypoglycemic actions of sulfonylurea therapy. To study the pharmacogenetic mechanism(s), we have investigated glibenclamide-induced insulin secretion, glibenclamide clearance from the blood, and glibenclamide metabolism in wild-type and Hnf-1alpha-deficient mice. We show that despite a profound defect in glucose-stimulated insulin secretion, diabetic Hnf-1alpha(-/-) mice have a robust glibenclamide-induced insulin secretory response. We demonstrate that the half-life (t(1/2)) of glibenclamide in the blood is increased in Hnf-1alpha(-/-) mice compared with wild-type littermates (3.9 +/- 1.3 vs. 1.5 +/- 1.8 min, P <or= 0.05). The clearance of glibenclamide from the blood during the first hours after intravenous administration was reduced approximately fourfold in Hnf-1alpha(-/-) mice compared with Hnf-1alpha(+/+) littermates. Glibenclamide uptake into hepatocytes was dramatically decreased in vivo and in vitro. To study the metabolism of glibenclamide in Hnf-1alpha(-/-) animals, we analyzed liver extracts from [(3)H]glibenclamide-injected animals by reverse-phase chromatography. We found that the ratio of the concentrations of glibenclamide and its metabolites was moderately increased in livers of Hnf-1alpha(-/-) mice, suggesting that hepatic glibenclamide metabolism was not impaired in animals with Hnf-1alpha deficiency. Our data demonstrate that high serum glibenclamide concentrations and an increased t(1/2) of glibenclamide in the blood of Hnf-1alpha(-/-) mice are caused by a defect in hepatic uptake of glibenclamide. This suggests that hypersensitivity to sulfonylureas in MODY3 patients may be due to impaired hepatic clearance and elevated plasma concentrations of the drug.

Heterogeneity in young adult onset diabetes: aetiology alters clinical characteristics

AIMS

To describe the characteristics of hepatocyte nuclear factor (HNF) 1 alpha mutation carriers diagnosed with diabetes after 25 years and compare them with young-onset Type 2 diabetic patients (YT2D) diagnosed at the same age.

SUBJECTS AND METHODS

We studied 44 (21 male, 23 female) patients with HNF-1 alpha mutations diagnosed with diabetes at ages 25-45 years and 44 YT2D subjects matched for sex and age of diagnosis.

RESULTS

Median age of onset of diabetes was 35 years in both groups. The HNF-1 alpha group demonstrated: lower body mass index (25.1 vs. 30.7 kg/m2; P < 0.001) and lower fasting triglycerides (1.37 vs. 2.96 mmol/l; P = 0.001) with similar fasting cholesterol level. They had lower glycated haemoglobin A1c (7.3 vs. 8.5%; P = 0.015) despite greater duration of diabetes (24 vs. 16 years; P = 0.02) and less frequent treatment with insulin (21% vs. 55%; P = 0.002). They were less likely to be treated for hypertension (13.3% vs. 56.3%; P = 0.009). Importantly, no difference was observed in reported parental history of diabetes between the two groups (65.9% vs. 63.6%; P = 0.92). Logistic regression showed that triglyceride levels and presence of anti-hypertensive treatment were the most important independent variables.

CONCLUSIONS

Patients with HNF-1 alpha mutations may present with diabetes as young adults between the ages of 25-45 years. In this age range a wide differential diagnosis of diabetes is observed. Conventional criteria of age of onset and family history will not differentiate HNF-1 alpha mutation carriers from YT2D subjects in this age range, but features of the metabolic syndrome, in particular fasting triglycerides and hypertension, are helpful. In patients diagnosed before 45 years without features of insulin resistance the diagnosis of HNF-1 alpha should be considered.

The role of transcription factors in maturity-onset diabetes of the young

The study of maturity-onset diabetes of the young (MODY), an autosomal dominant form of early-onset diabetes mellitus characterised by defective insulin secretion has been extremely successful in two ways. Firstly it has enabled definitive diagnosis for patients. This allows more accurate prediction of disease and treatment requirements. Secondly it has facilitated an increased understanding of the genes and pathways that are crucial for normal beta-cell function. Five of the six MODY genes, TCF1 (encoding HNF-1alpha), TCF2 (encoding HNF-1beta) HNF4A, insulin promoter factor (IPF)1, and NEUROD1, are transcription factors that operate in a complex network of gene regulation. Several genes have been shown to be regulated by the MODY transcription factors in a beta-cell specific manner. This includes the co-regulation of HNF-1alpha and HNF-4alpha by each other. The exact mechanism of how mutations in these transcription factors result in diabetes in humans remains unknown. However, current opinion favours pleiotropic adverse effects on many genes; extensive in vitro and in vivo studies of these genes has highlighted their importance in both glucose sensing-insulin secretion coupling and maintaining the fully differentiated beta-cell phenotype.

A genetic switch in pancreatic beta-cells: implications for differentiation and haploinsufficiency

Heterozygous mutations in the genes encoding transcriptional regulators hepatocyte nuclear factor (HNF)-1alpha and HNF-4alpha cause a form of diabetes known as maturity-onset diabetes of the young (MODY). Haploinsufficiency of HNF-1alpha or HNF-4alpha results in MODY because of defective function of pancreatic islet cells. In contrast, homozygous null mutations in mouse models lead to widespread and profound gene expression defects in multiple cell types. Thus, it is not surprising that HNF-1alpha function is now known to have distinct properties in pancreatic beta-cells. It controls a complex tissue-selective genetic network that is activated when pancreatic cells differentiate, and allows these cells to maintain critical specialized functions. The network contains an indispensable core component formed by a positive cross-regulatory feedback circuit between HNF-1alpha and HNF-4alpha. This type of circuit configuration can exhibit a switch-like behavior with two stable states. In the default active state, it can serve to perpetuate network activity in differentiated beta-cells. However, the loss of one HNF-1alpha or HNF-4alpha allele can increase the probability that the feedback circuit is permanently switched off, resulting in decreased expression of all four alleles selectively in beta-cells. Such a model can serve to rationalize key aspects of the pathogenic mechanism in MODY.

Diabetes Mellitus do Tipo MODY

Estima-se que perto de 5% dos indivíduos classificados como portadores de diabetes mellitus (DM) tipo 2 e 10% daqueles considerados como tipo 1 (anteriormente classificado como juvenil) sejam, na verdade, portadores de mutações MODY. Nesta forma de DM ocorre uma co-segregação evidente de algumas mutações com a hiperglicemia, fato este reproduzido em inúmeras famílias estudadas em várias populações do mundo. Caracteriza-se por ser uma das poucas causas de DM cujo modo de transmissão da predisposição genética ocorre de uma forma autossômica-dominante, compondo o grupo chamado de DM monogênicos, onde os outros representantes têm uma prevalência bastante rara. As mutações nos genes MODY, mesmo no estado heterozigoto, apresentam um forte impacto no fenótipo (alta penetrância), sendo que 95% dos indivíduos nascidos com alguma mutação MODY serão diabéticos ou apresentarão alterações no âmbito do metabolismo glicídico antes dos 55 anos de idade. Este trabalho objetiva a discussão desta forma de DM, enfatizando suas características clínicas e genéticas mais relevantes. A pesquisa sistemática de mutações MODY começa a ser feita de forma rotineira em vários países, havendo uma tendência de se colocar este recurso diagnóstico como um exame na prática da diabetologia.

Maturity-onset diabetes of the young: from clinical description to molecular genetic characterization

Maturity-onset diabetes of the young is a heterogeneous group of autosomal dominantly inherited, young-onset beta-cell disorders. At least two consecutive generations are affected with a family member diagnosed before 25 years of age. Diabetes is caused either by mutations in the glucokinase gene (glucokinase MODY) or by mutations in transcription factors (transcription factor MODY). Glucokinase maturity-onset diabetes of the young is a mild, non-progressive hyperglycaemia caused by a resetting of the pancreatic glucose sensor. It is treated with diet, and complications are rare. Pregnancies affected by glucokinase mutations have specific management strategies and prognosis. Transcription factor maturity-onset diabetes of the young, caused by mutations in the hepatocyte nuclear factor genes HNF-1alpha, HNF-4alpha and HNF-1beta, and in insulin promoter factor-1 results in a progressive beta-cell defect with increasing treatment requirements and diabetic complications. Cystic renal disease is a prominent feature of HNF-1beta mutations. Further maturity-onset diabetes of the young genes remain to be identified. MODY is part of the differential diagnosis of diabetes presenting in the first to third decades of life. Diagnostic molecular genetic testing is available for the more common genes involved.

Predictive genetic testing in maturity-onset diabetes of the young (MODY)

INTRODUCTION

Maturity-onset diabetes of the young (MODY) is characterized by autosomal dominant inheritance of young-onset non-insulin-dependent diabetes. It accounts for approximately 1% of Type 2 diabetes (approximately 20 000 people in the UK). Diagnostic and predictive genetic tests are now possible for 80% of MODY families. Diagnostic tests can be helpful as the diagnosis can be confirmed and the subtype defined which has implications for treatment and prognosis. However predictive genetic testing, particularly in children, raises many scientific, ethical and practical questions.

METHODS

This is a case report of a family with diabetes resulting from an hepatic nuclear factor (HNF)1alpha mutation, who request a predictive test in their 5-year-old daughter. The scientific issues arising from molecular genetic testing in MODY are discussed, along with the process of genetic counselling. The views of the family and the clinical genetics team involved are presented.

RESULTS

The implications of positive and negative predictive test results and the possibility of postponing the test were among many issues discussed during genetic counselling. The family remained convinced the test was appropriate for their daughter and the clinical genetics team fully supported this decision. The family, motivated by their family history of diabetes and personal experiences of the disease, wished to reduce uncertainty about their daughter's future irrespective of the result.

CONCLUSIONS

This case emphasizes that decisions on predictive testing are very personal and require appropriate counselling.