Urinary C-peptide creatinine ratio is a practical outpatient tool for identifying hepatocyte nuclear factor 1-{alpha}/hepatocyte nuclear factor 4-{alpha} maturity-onset diabetes of the young from long-duration type 1 diabetes

Maturity-onset diabetes of the young (MODY) in Brazil: Establishment of a national registry and appraisal of available genetic and clinical data

AIMS

Maturity-Onset Diabetes of the Young (MODY) comprises a heterogeneous group of monogenic forms of diabetes caused by mutations in at least 14 genes, but mostly by mutations in Glucokinase (GCK) and hepatocyte nuclear factor-1 homeobox A (HNF1A). This study aims to establish a national registry of MODY cases in Brazilian patients, assessing published and unpublished data.

METHODS

311 patients with clinical characteristics of MODY were analyzed, with unpublished data on 298 individuals described in 12 previous publications and 13 newly described cases in this report.

RESULTS

72 individuals had GCK mutations, 9 described in Brazilian individuals for the first time. One previously unpublished novel GCK mutation, Gly178Ala, was found in one family. 31 individuals had HNF1A mutations, 2 described for the first time in Brazilian individuals. Comparisons of GCK probands vs HNF1A: age 16±11 vs 35±20years; age at diagnosis 11±8 vs 21±7years; BMI 19±6 vs 25±6kg/m²; sulfonylurea users 5 vs 83%; insulin users 5 vs 17%; presence of arterial hypertension 0 vs. 33%, all p<0.05. No differences were observed in lipids and C-peptide.

CONCLUSIONS

Most MODY cases in Brazil are due to GCK mutations. In agreement with other studied populations, novel mutations are common. Only 14% of patients with familial diabetes carry a HNF1A mutation. Diagnosis of other rare forms of MODY is still a challenge in Brazilian population, as well as adequate strategies to screen individuals for molecular diagnosis.

Random non-fasting C-peptide: bringing robust assessment of endogenous insulin secretion to the clinic

BACKGROUND

Measuring endogenous insulin secretion using C-peptide can assist diabetes management, but standard stimulation tests are impractical for clinical use. Random non-fasting C-peptide assessment would allow testing when a patient is seen in clinic.

METHODS

We compared C-peptide at 90 min in the mixed meal tolerance test (sCP) with random non-fasting blood C-peptide (rCP) and random non-fasting urine C-peptide creatinine ratio (rUCPCR) in 41 participants with insulin-treated diabetes [median age 72 (interquartile range 68-78); diabetes duration 21 (14-31) years]. We assessed sensitivity and specificity for previously reported optimal mixed meal test thresholds for severe insulin deficiency (sCP < 200 pmol//l) and Type 1 diabetes/inability to withdraw insulin (< 600 pmol//l), and assessed the impact of concurrent glucose.

RESULTS

rCP and sCP levels were similar (median 546 and 487 pmol//l, P = 0.92). rCP was highly correlated with sCP, r = 0.91, P < 0.0001, improving to r = 0.96 when excluding samples with concurrent glucose < 8 mmol//l. An rCP cut-off of 200 pmol//l gave 100% sensitivity and 93% specificity for detecting severe insulin deficiency, with area under the receiver operating characteristic curve of 0.99. rCP < 600 pmol//l gave 87% sensitivity and 83% specificity to detect sCP < 600 pmol//l. Specificity improved to 100% when excluding samples with concurrent glucose < 8 mmol//l. rUCPCR (0.52 nmol/mmol) was also well-correlated with sCP, r = 0.82, P < 0.0001. A rUCPCR cut-off of < 0.2 nmol/ mmol gave sensitivity and specificity of 83% and 93% to detect severe insulin deficiency, with area under the receiver operating characteristic curve of 0.98.

CONCLUSIONS

Random non-fasting C-peptide measures are strongly correlated with mixed meal C-peptide, and have high sensitivity and specificity for identifying clinically relevant thresholds. These tests allow assessment of C-peptide at the point patients are seen for clinical care.

Systematic Population Screening, Using Biomarkers and Genetic Testing, Identifies 2.5% of the U.K. Pediatric Diabetes Population With Monogenic Diabetes

OBJECTIVE

Monogenic diabetes is rare but is an important diagnosis in pediatric diabetes clinics. These patients are often not identified as this relies on the recognition of key clinical features by an alert clinician. Biomarkers (islet autoantibodies and C-peptide) can assist in the exclusion of patients with type 1 diabetes and allow systematic testing that does not rely on clinical recognition. Our study aimed to establish the prevalence of monogenic diabetes in U.K. pediatric clinics using a systematic approach of biomarker screening and targeted genetic testing.

RESEARCH DESIGN AND METHODS

We studied 808 patients (79.5% of the eligible population) <20 years of age with diabetes who were attending six pediatric clinics in South West England and Tayside, Scotland. Endogenous insulin production was measured using the urinary C-peptide creatinine ratio (UCPCR). C-peptide-positive patients (UCPCR ≥0.2 nmol/mmol) underwent islet autoantibody (GAD and IA2) testing, with patients who were autoantibody negative undergoing genetic testing for all 29 identified causes of monogenic diabetes.

RESULTS

A total of 2.5% of patients (20 of 808 patients) (95% CI 1.6-3.9%) had monogenic diabetes (8 GCK, 5 HNF1A, 4 HNF4A, 1 HNF1B, 1 ABCC8, 1 INSR). The majority (17 of 20 patients) were managed without insulin treatment. A similar proportion of the population had type 2 diabetes (3.3%, 27 of 808 patients).

CONCLUSIONS

This large systematic study confirms a prevalence of 2.5% of patients with monogenic diabetes who were <20 years of age in six U.K. clinics. This figure suggests that ∼50% of the estimated 875 U.K. pediatric patients with monogenic diabetes have still not received a genetic diagnosis. This biomarker screening pathway is a practical approach that can be used to identify pediatric patients who are most appropriate for genetic testing.

Type 1 Diabetes Genetic Risk Score: A Novel Tool to Discriminate Monogenic and Type 1 Diabetes

Distinguishing patients with monogenic diabetes from those with type 1 diabetes (T1D) is important for correct diagnosis, treatment, and selection of patients for gene discovery studies. We assessed whether a T1D genetic risk score (T1D-GRS) generated from T1D-associated common genetic variants provides a novel way to discriminate monogenic diabetes from T1D. The T1D-GRS was highly discriminative of proven maturity-onset diabetes of young (MODY) (n = 805) and T1D (n = 1,963) (receiver operating characteristic area under the curve 0.87). A T1D-GRS of >0.280 (>50th T1D centile) was indicative of T1D (94% specificity, 50% sensitivity). We then analyzed the T1D-GRS of 242 white European patients with neonatal diabetes (NDM) who had been tested for all known NDM genes. Monogenic NDM was confirmed in 90, 59, and 8% of patients with GRS <5th T1D centile, 50-75th T1D centile, and >75th T1D centile, respectively. Applying a GRS 50th T1D centile cutoff in 48 NDM patients with no known genetic cause identified those most likely to have a novel monogenic etiology by highlighting patients with probable early-onset T1D (GRS >50th T1D centile) who were diagnosed later and had less syndromic presentation but additional autoimmune features compared with those with proven monogenic NDM. The T1D-GRS is a novel tool to improve the use of biomarkers in the discrimination of monogenic diabetes from T1D.

Urinary C-Peptide/Creatinine Ratio Can Distinguish Maturity-Onset Diabetes of the Young from Type 1 Diabetes in Children and Adolescents: A Single-Center Experience

BACKGROUND

The urinary C-peptide/creatinine ratio (UCPCR) and fasting C-peptide level can assess beta-cell function in clinical practice. In the present study, the use of the UCPCR and fasting C-peptide levels was investigated in the differential diagnosis between maturity-onset diabetes of the young (MODY) and type 1 diabetes mellitus (T1DM).

METHODS

Twenty-seven patients with genetically confirmed MODY by next-generation sequence analysis and 42 children with T1DM were included. C-peptide levels were measured after an overnight fast before breakfast, and urine samples were collected 2 h after a standard lunch in the hospital.

RESULTS

The UCPCR in the T1DM group was 0.17 ± 0.5 nmol/mmol, and in the MODY group it was 1.27 ± 1.03 nmol/mmol (p = 0.001). The receiver operating characteristic (ROC) curves showed excellent discrimination (area under the curve 0.93). A UCPCR ≥0.22 nmol/mmol yielded a 96.3% sensitivity and an 85.7% specificity. The fasting C-peptide level in the T1DM group was lower than that in the MODY group (p = 0.001). The fasting C-peptide cutoff determined by ROC curve analysis was 0.62 ng/ml, with a sensitivity of 93% and a specificity of 90% for discriminating between MODY and T1DM.

CONCLUSIONS

We showed that the UCPCR and fasting C-peptide levels in children and adolescents can distinguish patients with MODY from patients with T1DM with high specificity and sensitivity. A value of UCPCR ≥0.22 nmol/mmol may indicate further genetic testing for MODY.

Post-glucose-load urinary C-peptide and glucose concentration obtained during OGTT do not affect oral minimal model-based plasma indices

The purpose of this study was to investigate how renal loss of both C-peptide and glucose during oral glucose tolerance test (OGTT) relate to and affect plasma-derived oral minimal model (OMM) indices. All individuals were recruited during family screening between August 2007 and January 2011 and underwent a 3.5-h OGTT, collecting nine plasma samples and urine during OGTT. We obtained the following three subgroups: normoglycemic, at risk, and T2D. We recruited South Asian and Caucasian families, and we report separate analyses if differences occurred. Plasma glucose, insulin, and C-peptide concentrations were analyzed as AUCs during OGTT, OMM estimate of renal C-peptide secretion, and OMM beta-cell and insulin sensitivity indices were calculated to obtain disposition indices. Post-glucose load glucose and C-peptide in urine were measured and related to plasma-based indices. Urinary glucose corresponded well with plasma glucose AUC (Cau r = 0.64, P < 0.01; SA r = 0.69, P < 0.01), S I (Cau r = -0.51, P < 0.01; SA r = -0.41, P < 0.01), Φ dynamic (Cau r = -0.41, P < 0.01; SA r = -0.57, P < 0.01), and Φ oral (Cau r = -0.61, P < 0.01; SA r = -0.73, P < 0.01). Urinary C-peptide corresponded well to plasma C-peptide AUC (Cau r = 0.45, P < 0.01; SA r = 0.33, P < 0.05) and OMM estimate of renal C-peptide secretion (r = 0.42, P < 0.01). In general, glucose excretion plasma threshold for the presence of glucose in urine was ~10-10.5 mmol L(-1) in non-T2D individuals, but not measurable in T2D individuals. Renal glucose secretion during OGTT did not influence OMM indices in general nor in T2D patients (renal clearance range 0-2.1 %, with median 0.2 % of plasma glucose AUC). C-indices of urinary glucose to detect various stages of glucose intolerance were excellent (Cau 0.83-0.98; SA 0.75-0.89). The limited role of renal glucose secretion validates the neglecting of urinary glucose secretion in kinetic models of glucose homeostasis using plasma glucose concentrations. Both C-peptide and glucose in urine collected during OGTT might be used as non-invasive measures for endogenous insulin secretion and glucose tolerance state.

Detection of C-Peptide in Urine as a Measure of Ongoing Beta Cell Function

C-peptide is a protein secreted by the pancreatic beta cells in equimolar quantities with insulin, following the cleavage of proinsulin into insulin. Measurement of C-peptide is used as a surrogate marker of endogenous insulin secretory capacity. Assessing C-peptide levels can be useful in classifying the subtype of diabetes as well as assessing potential treatment choices in the management of diabetes.Standard measures of C-peptide involve blood samples collected either fasted or, most often, after a fixed stimulus (such as oral glucose, mixed meal, or IV glucagon). Despite the established clinical utility of blood C-peptide measurement, its widespread use is limited. In many instances this is due to perceived practical restrictions associated with sample collection.Urine C-peptide measurement is an attractive noninvasive alternative to blood measures of beta-cell function. Urine C-peptide creatinine ratio measured in a single post stimulated sample has been shown to be a robust, reproducible measure of endogenous C-peptide which is stable for three days at room temperature when collected in boric acid. Modern high sensitivity immunoassay technologies have facilitated measurement of C-peptide down to single picomolar concentrations.

Recognition and Management of Individuals With Hyperglycemia Because of a Heterozygous Glucokinase Mutation

Glucokinase-maturity-onset diabetes of the young (GCK-MODY), also known as MODY2, is caused by heterozygous inactivating mutations in the GCK gene. GCK gene mutations are present in ∼1 in 1,000 of the population, but most are not diagnosed. They are common causes of MODY (10-60%): persistent incidental childhood hyperglycemia (10-60%) and gestational diabetes mellitus (1-2%). GCK-MODY has a unique pathophysiology and clinical characteristics, so it is best considered as a discrete genetic subgroup. People with GCK-MODY have a defect in glucose sensing; hence, glucose homeostasis is maintained at a higher set point resulting in mild, asymptomatic fasting hyperglycemia (5.4-8.3 mmol/L, HbA1c range 5.8-7.6% [40-60 mmol/mol]), which is present from birth and shows slight deterioration with age. Even after 50 years of mild hyperglycemia, people with GCK-MODY do not develop significant microvascular complications, and the prevalence of macrovascular complications is probably similar to that in the general population. Treatment is not recommended outside pregnancy because glucose-lowering therapy is ineffective in people with GCK-MODY and there is a lack of long-term complications. In pregnancy, fetal growth is primarily determined by whether the fetus inherits the GCK gene mutation from their mother. Insulin treatment of the mother is only appropriate when increased fetal abdominal growth on scanning suggests the fetus is unaffected. The impact on outcome of maternal insulin treatment is limited owing to the difficulty in altering maternal glycemia in these patients. Making the diagnosis of GCK-MODY through genetic testing is essential to avoid unnecessary treatment and investigations, especially when patients are misdiagnosed with type 1 or type 2 diabetes.

Adolescent non-adherence reveals a genetic cause for diabetes

BACKGROUND

Glucokinase related maturity-onset diabetes of the young (GCK-MODY) is a form of monogenic diabetes characterized by mildly elevated fasting blood sugars and HbA(1c) typically ranging from 38 to 60 mmol/mol (5.6-7.6%). It is frequently unrecognized or misdiagnosed as Type 1 or Type 2 diabetes, resulting in unnecessary pharmacologic therapy.

CASE REPORT

Two brothers were initially diagnosed with Type 1 diabetes mellitus. The brothers were maintained on a total daily insulin dose of 0.3-0.5 units/kg/day and had HbA(1c) values of 40-51 mmol/mol (5.8-6.8%) throughout childhood. After over 10 years of insulin treatment, the younger brother chose to discontinue his insulin therapy without informing his family or his clinician. Following cessation of insulin treatment, he did not experience any change in overall glycaemic control. Subsequent research-based genetic testing revealed a deleterious mutation in GCK in both brothers (p.Val182Met). The older brother subsequently discontinued insulin therapy and both have remained off all pharmacological therapy with good glycaemic control (HbA(1c) < 53 mmol/mol, < 7%) and no adverse complications. The family was advised to seek confirmatory genetic testing in the father and other relatives with hyperglycaemia.

CONCLUSION

The family described above exemplifies the rationale behind considering a genetic cause when evaluating every person with new-onset hyperglycaemia or those with atypical diabetes. The cost of genetic testing for the most common MODY causing genes may be offset by savings made in therapeutic costs. It is important that all clinicians supervising diabetes care recognize the cardinal features that distinguish GCK-MODY from other forms of diabetes.

Identifying monogenic diabetes in a pediatric cohort with presumed type 1 diabetes

OBJECTIVE

Monogenic diabetes (MD) is rare and can often be confused with type 1 diabetes (T1D) in a pediatric cohort. We sought to determine clinical criteria that could optimally identify candidates for genetic testing of two common forms of MD that alter therapy: glucokinase (GCK) and hepatocyte nuclear factor 1 alpha (HNF1α).

RESEARCH DESIGN AND METHODS

We performed a retrospective chart review of 939 patients with a presumed diagnosis of T1D, 6 months-20 yr of age, and identified four clinical criteria that were unusual for T1D and could warrant further evaluation for MD: (i) negative pancreatic autoantibodies, (ii) evidence of prolonged endogenous insulin production, or (iii) strong family history of diabetes in multiple generations. One hundred and twenty-one patients were identified as having one or more of these high-risk clinical criteria and were offered screening for mutations in GCK and HNF1α; 58 consented for genetic testing.

RESULTS

Of 58 patients with presumed T1D who underwent genetic testing, four were found to have GCK and one had HNF1α. No patients with only one high-risk feature were found to have MD. Of 10 patients who had two or more high risk criteria, five had MD (50%).

CONCLUSION

A high frequency of MD from mutations in GCK/HNF1α may be identified among pediatric diabetic patients originally considered to have T1D by performing genetic testing on those patients with multiple clinical risk factors for MD.

Most people with long-duration type 1 diabetes in a large population-based study are insulin microsecretors

OBJECTIVE

Small studies using ultrasensitive C-peptide assays suggest endogenous insulin secretion is frequently detectable in patients with long-standing type 1 diabetes (T1D), but these studies do not use representative samples. We aimed to use the stimulated urine C-peptide-to-creatinine ratio (UCPCR) to assess C-peptide levels in a large cross-sectional, population-based study of patients with T1D.

RESEARCH DESIGN AND METHODS

We recruited 924 patients from primary and secondary care in two U.K. centers who had a clinical diagnosis of T1D, were under 30 years of age when they received a diagnosis, and had a diabetes duration of >5 years. The median age at diagnosis was 11 years (interquartile range 6-17 years), and the duration of diabetes was 19 years (11-27 years). All provided a home postmeal UCPCR, which was measured using a Roche electrochemiluminescence assay.

RESULTS

Eighty percent of patients (740 of 924 patients) had detectable endogenous C-peptide levels (UCPCR >0.001 nmol/mmol). Most patients (52%, 483 of 924 patients) had historically very low undetectable levels (UCPCR 0.0013-0.03 nmol/mmol); 8% of patients (70 of 924 patients) had a UCPCR ≥0.2 nmol/mmol, equivalent to serum levels associated with reduced complications and hypoglycemia. Absolute UCPCR levels fell with duration of disease. Age at diagnosis and duration of disease were independent predictors of C-peptide level in multivariate modeling.

CONCLUSIONS

This population-based study shows that the majority of long-duration T1D patients have detectable urine C-peptide levels. While the majority of patients are insulin microsecretors, some maintain clinically relevant endogenous insulin secretion for many years after the diagnosis of diabetes. Understanding this may lead to a better understanding of pathogenesis in T1D and open new possibilities for treatment.

The effect of insulin resistance on postprandial triglycerides in Korean type 2 diabetic patients

We hypothesized that the influence of metabolic parameters depends on metabolic syndrome (MetS) status. The clinical and metabolic implications of postprandial triglyceride (ppTG) in Korean type 2 diabetes were investigated in the presence or absence of MetS, MetS+, or MetS-. To investigate the relationship between ppTG and metabolic parameters, we analyzed plasma TG levels in 126 newly diagnosed, drug-naïve diabetic patients after ingestion of a standardized low calorie and fat (500 kcal, 17.5 g fat) liquid meal formula. We report that MetS+ patients have significantly higher BMI, waist/hip ratio, HOMA-IR, and HOMA-β, but insignificantly higher fasting TG, ppTG, and ΔTG than MetS- patients. In the MetS+ patients, ppTG correlated with fasting TG and non-HDL, but was not related to HOMA-IR. In MetS- patients, ppTG correlated with fasting TG, non-HDL, blood pressure, waist/hip ratio, fasting C-peptide and insulin levels, and HOMA-IR. Multivariate analysis showed HOMA-IR to be a predictive factor for ppTG in MetS- patients but not in MetS+ patients. ppTG correlated with IR in MetS- type 2 diabetic patients but not in MetS+. This unexpected result implies that MetS+ diabetic patients already have high fasting TG and that IR influences fasting TG more dominantly than ppTG.

The majority of patients with long-duration type 1 diabetes are insulin microsecretors and have functioning beta cells

AIMS/HYPOTHESIS

Classically, type 1 diabetes is thought to proceed to absolute insulin deficiency. Recently developed ultrasensitive assays capable of detecting C-peptide under 5 pmol/l now allow very low levels of C-peptide to be detected in patients with long-standing type 1 diabetes. It is not known whether this low-level endogenous insulin secretion responds to physiological stimuli. We aimed to assess how commonly low-level detectable C-peptide occurs in long-duration type 1 diabetes and whether it responds to a meal stimulus.

METHODS

We performed a mixed-meal tolerance test in 74 volunteers with long-duration (>5 years) type 1 diabetes, i.e. with age at diagnosis 16 (9-23) years (median [interquartile range]) and diabetes duration of 30 (19-41) years. We assessed fasting and stimulated serum C-peptide levels using an electrochemiluminescence assay (detection limit 3.3 pmol/l), and also the urinary C-peptide:creatinine ratio (UCPCR).

RESULTS

Post-stimulation serum C-peptide was detectable at very low levels (>3.3 pmol/l) in 54 of 74 (73%) patients. In all patients with detectable serum C-peptide, C-peptide either increased (n = 43, 80%) or stayed the same (n = 11) in response to a meal, with no indication of levels falling (p < 0.0001). With increasing disease duration, absolute C-peptide levels fell although the numbers with detectable C-peptide remained high (68%, i.e. 25 of 37 patients with >30 years duration). Similar results were obtained for UCPCR.

CONCLUSIONS/INTERPRETATION

Most patients with long-duration type 1 diabetes continue to secrete very low levels of endogenous insulin, which increase after meals. This is consistent with the presence of a small number of still functional beta cells and implies that beta cells are either escaping immune attack or undergoing regeneration.

Cost-effectiveness of MODY genetic testing: translating genomic advances into practical health applications

OBJECTIVE To evaluate the cost-effectiveness of a genetic testing policy for HNF1A-, HNF4A-, and GCK-MODY in a hypothetical cohort of type 2 diabetic patients 25-40 years old with a MODY prevalence of 2%. RESEARCH DESIGN AND METHODS We used a simulation model of type 2 diabetes complications based on UK Prospective Diabetes Study data, modified to account for the natural history of disease by genetic subtype to compare a policy of genetic testing at diabetes diagnosis versus a policy of no testing. Under the screening policy, successful sulfonylurea treatment of HNF1A-MODY and HNF4A-MODY was modeled to produce a glycosylated hemoglobin reduction of -1.5% compared with usual care. GCK-MODY received no therapy. Main outcome measures were costs and quality-adjusted life years (QALYs) based on lifetime risk of complications and treatments, expressed as the incremental cost-effectiveness ratio (ICER) (USD/QALY). RESULTS The testing policy yielded an average gain of 0.012 QALYs and resulted in an ICER of 205,000 USD. Sensitivity analysis showed that if the MODY prevalence was 6%, the ICER would be ~50,000 USD. If MODY prevalence was >30%, the testing policy was cost saving. Reducing genetic testing costs to 700 USD also resulted in an ICER of ~50,000 USD. CONCLUSIONS Our simulated model suggests that a policy of testing for MODY in selected populations is cost-effective for the U.S. based on contemporary ICER thresholds. Higher prevalence of MODY in the tested population or decreased testing costs would enhance cost-effectiveness. Our results make a compelling argument for routine coverage of genetic testing in patients with high clinical suspicion of MODY.

The spectrum of HNF1A gene mutations in Greek patients with MODY3: relative frequency and identification of seven novel germline mutations

OBJECTIVE

Maturity-Onset Diabetes of the Young (MODY) is the most common type of monogenic diabetes accounting for 1-2% of the population with diabetes. The relative incidence of HNF1A-MODY (MODY3) is high in European countries; however, data are not available for the Greek population. The aims of this study were to determine the relative frequency of MODY3 in Greece, the type of the mutations observed, and their relation to the phenotype of the patients.

DESIGN AND METHODS

Three hundred ninety-five patients were referred to our center because of suspected MODY during a period of 15 yr. The use of Denaturing Gradient Gel Electrophoresis of polymerase chain reaction amplified DNA revealed 72 patients carrying Glucokinase gene mutations (MODY2) and 8 patients carrying HNF1A gene mutations (MODY3). After using strict criteria, 54 patients were selected to be further evaluated by direct sequencing or by multiplex ligation probe amplification (MLPA) for the presence of HNF1A gene mutations.

RESULTS

In 16 unrelated patients and 13 of their relatives, 15 mutations were identified in the HNF1A gene. Eight of these mutations were previously reported, whereas seven were novel. Clinical features, such as age of diabetes at diagnosis or severity of hyperglycemia, were not related to the mutation type or location.

CONCLUSIONS

In our cohort of patients fulfilling strict clinical criteria for MODY, 12% carried an HNF1A gene mutation, suggesting that defects of this gene are responsible for a significant proportion of monogenic diabetes in the Greek population. No clear phenotype-genotype correlations were identified.

Prevalence, characteristics and clinical diagnosis of maturity onset diabetes of the young due to mutations in HNF1A, HNF4A, and glucokinase: results from the SEARCH for Diabetes in Youth

AIMS

Our study aims were to determine the frequency of MODY mutations (HNF1A, HNF4A, glucokinase) in a diverse population of youth with diabetes and to assess how well clinical features identify youth with maturity-onset diabetes of the young (MODY).

METHODS

The SEARCH for Diabetes in Youth study is a US multicenter, population-based study of youth with diabetes diagnosed at age younger than 20 years. We sequenced genomic DNA for mutations in the HNF1A, HNF4A, and glucokinase genes in 586 participants enrolled in SEARCH between 2001 and 2006. Selection criteria included diabetes autoantibody negativity and fasting C-peptide levels of 0.8 ng/mL or greater.

RESULTS

We identified a mutation in one of three MODY genes in 47 participants, or 8.0% of the tested sample, for a prevalence of at least 1.2% in the pediatric diabetes population. Of these, only 3 had a clinical diagnosis of MODY, and the majority was treated with insulin. Compared with the MODY-negative group, MODY-positive participants had lower FCP levels (2.2 ± 1.4 vs 3.2 ± 2.1 ng/mL, P < .01) and fewer type 2 diabetes-like metabolic features. Parental history of diabetes did not significantly differ between the 2 groups.

CONCLUSIONS/INTERPRETATION

In this systematic study of MODY in a large pediatric US diabetes cohort, unselected by referral pattern or family history, MODY was usually misdiagnosed and incorrectly treated with insulin. Although many type 2 diabetes-like metabolic features were less common in the mutation-positive group, no single characteristic identified all patients with mutations. Clinicians should be alert to the possibility of MODY diagnosis, particularly in antibody-negative youth with diabetes.

Maturity onset diabetes of the young: identification and diagnosis

Maturity-onset diabetes of the young (MODY) is a monogenic disorder that results in a familial, young-onset non-insulin dependent form of diabetes, typically presenting in lean young adults before 25 years. Approximately 1% of diabetes has a monogenic cause but this is frequently misdiagnosed as Type 1 or Type 2 diabetes. A correct genetic diagnosis is important as it often leads to improved treatment for those affected with diabetes and enables predictive genetic testing for their asymptomatic relatives. An early diagnosis together with appropriate treatment is essential for reducing the risk of diabetic complications in later life. Mutations in the GCK and HNF1A/4 A genes account for up to 80% of all MODY cases. Mutations in the GCK gene cause a mild, asymptomatic and non-progressive fasting hyperglycaemia from birth usually requiring no treatment. In contrast, mutations in the genes encoding the transcription factors HNF1A and HNF4A cause a progressive insulin secretory defect and hyperglycaemia that can lead to vascular complications. The diabetes in these patients is usually well controlled with sulphonylurea tablets although insulin treatment may be required in later life. In this review, we outline the key clinical and laboratory characteristics of the common and rarer causes of MODY with the aim of raising awareness of this condition amongst health-care scientists.

The clinical utility of C-peptide measurement in the care of patients with diabetes

C-peptide is produced in equal amounts to insulin and is the best measure of endogenous insulin secretion in patients with diabetes. Measurement of insulin secretion using C-peptide can be helpful in clinical practice: differences in insulin secretion are fundamental to the different treatment requirements of Type 1 and Type 2 diabetes. This article reviews the use of C-peptide measurement in the clinical management of patients with diabetes, including the interpretation and choice of C-peptide test and its use to assist diabetes classification and choice of treatment. We provide recommendations for where C-peptide should be used, choice of test and interpretation of results. With the rising incidence of Type 2 diabetes in younger patients, the discovery of monogenic diabetes and development of new therapies aimed at preserving insulin secretion, the direct measurement of insulin secretion may be increasingly important. Advances in assays have made C-peptide measurement both more reliable and inexpensive. In addition, recent work has demonstrated that C-peptide is more stable in blood than previously suggested or can be reliably measured on a spot urine sample (urine C-peptide:creatinine ratio), facilitating measurement in routine clinical practice. The key current clinical role of C-peptide is to assist classification and management of insulin-treated patients. Utility is greatest after 3-5 years from diagnosis when persistence of substantial insulin secretion suggests Type 2 or monogenic diabetes. Absent C-peptide at any time confirms absolute insulin requirement and the appropriateness of Type 1 diabetes management strategies regardless of apparent aetiology.

Development of an economic evaluation of diagnostic strategies: the case of monogenic diabetes

OBJECTIVES

To describe the development process for defining an appropriate model structure for the economic evaluation of test-treatment strategies for patients with monogenic diabetes (caused by mutations in the GCK, HNF1A or HNF4A genes).

DESIGN

Experts were consulted to identify and define realistic test-treatment strategies and care pathways. A systematic assessment of published diabetes models was undertaken to inform the model structure.

SETTING

National Health Service in England and Wales.

PARTICIPANTS

Experts in monogenic diabetes whose collective expertise spans the length of the patient care pathway.

PRIMARY AND SECONDARY OUTCOMES

A defined model structure, including the test-treatment strategies, and the selection of a published diabetes model appropriate for the economic evaluation of strategies to identify patients with monogenic diabetes.

RESULTS

Five monogenic diabetes test-treatment strategies were defined: no testing of any kind, referral for genetic testing based on clinical features as noted by clinicians, referral for genetic testing based on the results of a clinical prediction model, referral for genetic testing based on the results of biochemical and immunological tests, referral for genetic testing for all patients with a diagnosis of diabetes under the age of 30 years. The systematic assessment of diabetes models identified the IMS CORE Diabetes Model (IMS CDM) as a good candidate for modelling the long-term outcomes and costs of the test-treatment strategies for monogenic diabetes. The short-term test-treatment events will be modelled using a decision tree which will feed into the IMS CDM.

CONCLUSIONS

Defining a model structure for any economic evaluation requires decisions to be made. Expert consultation and the explicit use of critical appraisal can inform these decisions. Although arbitrary choices have still been made, decision modelling allows investigation into such choices and the impact of assumptions that have to be made due to a lack of data.

Pathogenesis of the metabolic syndrome: insights from monogenic disorders

Identifying rare human metabolic disorders that result from a single-gene defect has not only enabled improved diagnostic and clinical management of such patients, but also has resulted in key biological insights into the pathophysiology of the increasingly prevalent metabolic syndrome. Insulin resistance and type 2 diabetes are linked to obesity and driven by excess caloric intake and reduced physical activity. However, key events in the causation of the metabolic syndrome are difficult to disentangle from compensatory effects and epiphenomena. This review provides an overview of three types of human monogenic disorders that result in (1) severe, non-syndromic obesity, (2) pancreatic beta cell forms of early-onset diabetes, and (3) severe insulin resistance. In these patients with single-gene defects causing their exaggerated metabolic disorder, the primary defect is known. The lessons they provide for current understanding of the molecular pathogenesis of the common metabolic syndrome are highlighted.

Home urine C-peptide creatinine ratio (UCPCR) testing can identify type 2 and MODY in pediatric diabetes

BACKGROUND

Making the correct diabetes diagnosis in children is crucial for lifelong management. Type 2 diabetes and maturity onset diabetes of the young (MODY) are seen in the pediatric setting, and can be difficult to discriminate from type 1 diabetes. Postprandial urinary C-peptide creatinine ratio (UCPCR) is a non-invasive measure of endogenous insulin secretion that has not been tested as a diagnostic tool in children or in patients with diabetes duration <5 yr. We aimed to assess whether UCPCR can discriminate type 1 diabetes from MODY and type 2 in pediatric diabetes.

METHODS

Two-hour postprandial UCPCR was measured in 264 patients aged <21 yr (type 1, n = 160; type 2, n = 41; and MODY, n = 63). Receiver operating characteristic curves were used to identify the optimal UCPCR cutoff for discriminating diabetes subtypes.

RESULTS

UCPCR was lower in type 1 diabetes [0.05 (<0.03-0.39) nmol/mmol median (interquartile range)] than in type 2 diabetes [4.01 (2.84-5.74) nmol/mmol, p < 0.0001] and MODY [3.51 (2.37-5.32) nmol/mmol, p < 0.0001]. UCPCR was similar in type 2 diabetes and MODY (p = 0.25), so patients were combined for subsequent analyses. After 2-yr duration, UCPCR ≥ 0.7 nmol/mmol has 100% sensitivity [95% confidence interval (CI): 92-100] and 97% specificity (95% CI: 91-99) for identifying non-type 1 (MODY + type 2 diabetes) from type 1 diabetes [area under the curve (AUC) 0.997]. UCPCR was poor at discriminating MODY from type 2 diabetes (AUC 0.57).

CONCLUSIONS

UCPCR testing can be used in diabetes duration greater than 2 yr to identify pediatric patients with non-type 1 diabetes. UCPCR testing is a practical non-invasive method for use in the pediatric outpatient setting.

Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha and 4 alpha in maturity-onset diabetes of the young and hyperinsulinemic hypoglycemia

Maturity-onset diabetes of the young (MODY) is a monogenic disorder characterized by autosomal dominant inheritance of young-onset (typically <25 years), noninsulin-dependent diabetes due to defective insulin secretion. MODY is both clinically and genetically heterogeneous with mutations in at least 10 genes. Mutations in the HNF1A gene encoding hepatocyte nuclear factor-1 alpha are the most common cause of MODY in most adult populations studied. The number of different pathogenic HNF1A mutations totals 414 in 1,247 families. Mutations in the HNF4A gene encoding hepatocyte nuclear factor-4 alpha are a rarer cause of MODY with 103 different mutations reported in 173 families to date. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The HNF4A MODY phenotype has been expanded by the reports of macrosomia in ∼50% of babies, and more rarely, neonatal hyperinsulinemic hypoglycemia. The identification of an HNF1A or HNF4A gene mutation has important implications for clinical management in diabetes and pregnancy, but MODY is significantly underdiagnosed. Current research is focused on identifying biomarkers and developing probability models to identify those patients most likely to have MODY, until next generation sequencing technology enables cost-effective gene analysis for all patients with young onset diabetes.

Mutations in HNF1A result in marked alterations of plasma glycan profile

A recent genome-wide association study identified hepatocyte nuclear factor 1-α (HNF1A) as a key regulator of fucosylation. We hypothesized that loss-of-function HNF1A mutations causal for maturity-onset diabetes of the young (MODY) would display altered fucosylation of N-linked glycans on plasma proteins and that glycan biomarkers could improve the efficiency of a diagnosis of HNF1A-MODY. In a pilot comparison of 33 subjects with HNF1A-MODY and 41 subjects with type 2 diabetes, 15 of 29 glycan measurements differed between the two groups. The DG9-glycan index, which is the ratio of fucosylated to nonfucosylated triantennary glycans, provided optimum discrimination in the pilot study and was examined further among additional subjects with HNF1A-MODY (n = 188), glucokinase (GCK)-MODY (n = 118), hepatocyte nuclear factor 4-α (HNF4A)-MODY (n = 40), type 1 diabetes (n = 98), type 2 diabetes (n = 167), and nondiabetic controls (n = 98). The DG9-glycan index was markedly lower in HNF1A-MODY than in controls or other diabetes subtypes, offered good discrimination between HNF1A-MODY and both type 1 and type 2 diabetes (C statistic ≥ 0.90), and enabled us to detect three previously undetected HNF1A mutations in patients with diabetes. In conclusion, glycan profiles are altered substantially in HNF1A-MODY, and the DG9-glycan index has potential clinical value as a diagnostic biomarker of HNF1A dysfunction.

Systematic assessment of etiology in adults with a clinical diagnosis of young-onset type 2 diabetes is a successful strategy for identifying maturity-onset diabetes of the young

OBJECTIVE

Misdiagnosis of maturity-onset diabetes of the young (MODY) remains widespread, despite the benefits of optimized management. This cross-sectional study examined diagnostic misclassification of MODY in subjects with clinically labeled young adult-onset type 1 and type 2 diabetes by extending genetic testing beyond current guidelines.

RESEARCH DESIGN AND METHODS

Individuals were selected for diagnostic sequencing if they displayed features atypical for their diagnostic label. From 247 case subjects with clinically labeled type 1 diabetes, we sequenced hepatocyte nuclear factor 1 α (HNF1A) and hepatocyte nuclear factor 4 α (HNF4A) in 20 with residual β-cell function ≥ 3 years from diagnosis (random or glucagon-stimulated C-peptide ≥ 0.2 nmol/L). From 322 with clinically labeled type 2 diabetes, we sequenced HNF1A and HNF4A in 80 with diabetes diagnosed ≤ 30 years and/or diabetes diagnosed ≤ 45 years without metabolic syndrome. We also sequenced the glucokinase (GCK) in 40 subjects with mild fasting hyperglycemia.

RESULTS

In the type 1 diabetic group, two HNF1A mutations were found (0.8% prevalence). In type 2 diabetic subjects, 10 HNF1A, two HNF4A, and one GCK mutation were identified (4.0%). Only 47% of MODY case subjects identified met current guidelines for diagnostic sequencing. Follow-up revealed a further 12 mutation carriers among relatives. Twenty-seven percent of newly identified MODY subjects changed treatment, all with improved glycemic control (HbA(1c) 8.8 vs. 7.3% at 3 months; P = 0.02).

CONCLUSIONS

The systematic use of widened diagnostic testing criteria doubled the numbers of MODY case subjects identified compared with current clinical practice. The yield was greatest in young adult-onset type 2 diabetes. We recommend that all patients diagnosed before age 30 and with presence of C-peptide at 3 years' duration are considered for molecular diagnostic analysis.

The impact of gender on urine C-peptide creatinine ratio interpretation

BACKGROUND

Urinary C-peptide creatinine ratio (UCPCR) is a non-invasive and convenient way of assessing endogenous insulin production. Adjusting for urine creatinine levels allows for differences in urine concentration. Creatinine excretion is known to be higher in men due to gender differences in muscle mass. We investigated the impact of gender on UCPCR.

METHODS

One hundred and seventy-six subjects underwent a mixed meal tolerance test (MMTT). We looked at the relationship between UCPCR on urine C-peptide and creatinine excretion rates using timed post-meal urine samples. A further 415 subjects had two-hour post-meal UCPCR measurements in order to derive gender-specific percentiles for different diabetes subgroups and controls.

RESULTS

UCPCR was 1.48-fold higher in women (n=78) than men (n=98), median (interquartile range [IQR]): 1.88 (0.49-3.49) men versus 2.88 (1.58-4.91) nmol mmol(-1) women, P=0.01. This reflects a gender difference in creatinine excretion rates (11.5 [8.3-13.7] men versus 8.2 [5.6-9.1] women μmol min(-1) P<0.001). C-peptide excretion rate was similar in men and women (19.8 [5.2-37.0] versus 22.1 [7.4-40.5] pmol min(-1), P=0.7). UCPCR was higher in women in all subgroups defined by diabetes classification and treatment, except long-term type 1 diabetes in whom C-peptide secretion was minimal.

CONCLUSIONS

Gender affects UCPCR, with higher values found in women. This results from lower urine creatinine reflecting gender differences in muscle mass. This necessitates gender-specific ranges for accurate interpretation of UCPCR results.

The development and validation of a clinical prediction model to determine the probability of MODY in patients with young-onset diabetes

AIMS/HYPOTHESIS

Diagnosing MODY is difficult. To date, selection for molecular genetic testing for MODY has used discrete cut-offs of limited clinical characteristics with varying sensitivity and specificity. We aimed to use multiple, weighted, clinical criteria to determine an individual's probability of having MODY, as a crucial tool for rational genetic testing.

METHODS

We developed prediction models using logistic regression on data from 1,191 patients with MODY (n = 594), type 1 diabetes (n = 278) and type 2 diabetes (n = 319). Model performance was assessed by receiver operating characteristic (ROC) curves, cross-validation and validation in a further 350 patients.

RESULTS

The models defined an overall probability of MODY using a weighted combination of the most discriminative characteristics. For MODY, compared with type 1 diabetes, these were: lower HbA(1c), parent with diabetes, female sex and older age at diagnosis. MODY was discriminated from type 2 diabetes by: lower BMI, younger age at diagnosis, female sex, lower HbA(1c), parent with diabetes, and not being treated with oral hypoglycaemic agents or insulin. Both models showed excellent discrimination (c-statistic = 0.95 and 0.98, respectively), low rates of cross-validated misclassification (9.2% and 5.3%), and good performance on the external test dataset (c-statistic = 0.95 and 0.94). Using the optimal cut-offs, the probability models improved the sensitivity (91% vs 72%) and specificity (94% vs 91%) for identifying MODY compared with standard criteria of diagnosis <25 years and an affected parent. The models are now available online at www.diabetesgenes.org .

CONCLUSIONS/INTERPRETATION

We have developed clinical prediction models that calculate an individual's probability of having MODY. This allows an improved and more rational approach to determine who should have molecular genetic testing.

The lessons of early-onset monogenic diabetes for the understanding of diabetes pathogenesis

Monogenic diabetes consists of different subtypes of single gene disorders comprising a large spectrum of phenotypes, namely neonatal diabetes mellitus or monogenic diabetes of infancy, dominantly inherited familial forms of early-onset diabetes (called Maturity-Onset Diabetes of the Young) and rarer diabetes-associated syndromic diseases. All these forms diagnosed at a very-young age are unrelated to auto-immunity. Their genetic dissection has revealed major genes in developmental and/or functional processes of the pancreatic β-cell physiology, and various molecular mechanisms underlying the primary pancreatic defects. Most of these discoveries have had remarkable consequences on the patients care and patient's long-term condition with outstanding examples of successful genomic medicine, which are highlighted in this chapter. Increasing evidence also shows that frequent polymorphisms in or near monogenic diabetes genes may contribute to adult polygenic type 2 diabetes. In this regard, unelucidated forms of monogenic diabetes represent invaluable models for identifying new targets of β-cell dysfunction.

Validation of a single-sample urinary C-peptide creatinine ratio as a reproducible alternative to serum C-peptide in patients with Type 2 diabetes

AIMS

Serum C-peptide can be used in Type 2 diabetes as a measure of endogenous insulin secretion, but practicalities of collection limit its routine clinical use. Urine C-peptide creatinine ratio is a non-invasive alternative that is stable for at least 3 days at room temperature in boric acid preservative. We aimed to assess the utility of urine C-peptide creatinine ratio in individuals with Type 2 diabetes as an alternative to serum C-peptide.

METHODS

We assessed, in 77 individuals with Type 2 diabetes, the reproducibility of, and correlations between, fasting and postprandial urine C-peptide creatinine ratio and serum C-peptide, and the impact of renal impairment (estimated glomerular filtration rate < 60 ml min(-1) 1.73 m(-2)) on these correlations.

RESULTS

Urine C-peptide creatinine ratio was at least as reproducible as serum C-peptide [fasting coefficient of variation mean (95% CI): 28 (21-35)% vs. 38 (26-59)% and 2-h post-meal 26 (18-33)% vs. 27 (20-34)%. Urine C-peptide creatinine ratio 2 h post-meal was correlated with stimulated serum C-peptide, both the 2-h value (r = 0.64, P < 0.001) and the 2-h area under the C-peptide curve (r = 0.63, P < 0.001). The association seen was similar in patients with and without moderate renal impairment (P = 0.6).

CONCLUSIONS

In patients with Type 2 diabetes, a single urine C-peptide creatinine ratio is a stable, reproducible measure that is well correlated with serum C-peptide following meal stimulation, even if there is moderate renal impairment. Urine C-peptide creatinine ratio therefore has potential for use in clinical practice in the assessment of Type 2 diabetes.

Who should have genetic testing for maturity-onset diabetes of the young?

Maturity-onset diabetes of the young (MODY) is a clinically heterogeneous group of monogenic disorders characterized by autosomal dominant inheritance of young-onset, non-insulin-dependent diabetes. The genes involved are important in beta cell development, function and regulation and lead to disorders in glucose sensing and insulin secretion. Heterozygous GCK mutations cause impaired glucokinase activity resulting in stable, mild hyperglycaemia that rarely requires treatment. HNF1A mutations cause a progressive insulin secretory defect that is sensitive to sulphonylureas, most often resulting in improved glycaemic control compared with other diabetes treatment. MODY owing to mutations in the HNF4A gene results in a similar phenotype, including sensitivity to sulphonylurea treatment. HNF1B mutations most frequently cause developmental renal disease (particularly renal cysts) but may also cause MODY in isolation or may cause the renal cysts and diabetes syndrome (RCAD syndrome). Mutations in NEUROD1, PDX1 (IPF1), CEL and INS are rare causes of MODY. MODY is often misdiagnosed as type 1 or type 2 diabetes. However, a correct genetic diagnosis impacts treatment and identifies at-risk family members. Thus, it is important to consider a diagnosis of MODY in appropriate individuals and to pursue genetic testing to establish a molecular diagnosis.

High-sensitivity CRP discriminates HNF1A-MODY from other subtypes of diabetes

OBJECTIVE

Maturity-onset diabetes of the young (MODY) as a result of mutations in hepatocyte nuclear factor 1-α (HNF1A) is often misdiagnosed as type 1 diabetes or type 2 diabetes. Recent work has shown that high-sensitivity C-reactive protein (hs-CRP) levels are lower in HNF1A-MODY than type 1 diabetes, type 2 diabetes, or glucokinase (GCK)-MODY. We aim to replicate these findings in larger numbers and other MODY subtypes.

RESEARCH DESIGN AND METHODS

hs-CRP levels were assessed in 750 patients (220 HNF1A, 245 GCK, 54 HNF4-α [HNF4A], 21 HNF1-β (HNF1B), 53 type 1 diabetes, and 157 type 2 diabetes).

RESULTS

hs-CRP was lower in HNF1A-MODY (median [IQR] 0.3 [0.1-0.6] mg/L) than type 2 diabetes (1.40 [0.60-3.45] mg/L; P < 0.001) and type 1 diabetes (1.10 [0.50-1.85] mg/L; P < 0.001), HNF4A-MODY (1.45 [0.46-2.88] mg/L; P < 0.001), GCK-MODY (0.60 [0.30-1.80] mg/L; P < 0.001), and HNF1B-MODY (0.60 [0.10-2.8] mg/L; P = 0.07). hs-CRP discriminated HNF1A-MODY from type 2 diabetes with hs-CRP <0.75 mg/L showing 79% sensitivity and 70% specificity (receiver operating characteristic area under the curve = 0.84).

CONCLUSIONS

hs-CRP levels are lower in HNF1A-MODY than other forms of diabetes and may be used as a biomarker to select patients for diagnostic HNF1A genetic testing.