Maturity-onset Diabetes Of The Young Mutations Research Articles

7316 A Unique Presentation of Diabetes Mellitus in an 8-Year-Old Male Positive For 3 Different Mutations Related to MODY

Abstract Disclosure: R. Senguttuvan: None. A. Pamfil: None. Background: Maturity-Onset Diabetes of the Young (MODY) is the most common form of inherited non-autoimmune diabetes mellitus, characterized by autosomal dominant inheritance, young age at onset and beta cell dysfunction. There are at least 14 MODY mutations and we present a pediatric case not meeting criteria for type 1[T1DM] or type 2 diabetes mellitus[T2DM], who tested positive for mutations in 3 different genes known to cause MODY. Case: An 8-year-old male, born full term, 2776 grams and 48.3 cm, without history of neonatal hypoglycemia or hyperglycemia, was referred for new onset diabetes mellitus management. While undergoing evaluation for abdominal pain and constipation, he was found to have a fasting glucose of 126 mg/dL (7 mmol/L) and hemoglobin A1C of 6.5%. He endorsed polyuria, but no polydipsia. He had no clinical signs of insulin resistance (e.g., acanthosis nigricans) and a BMI of 23.65 kg/m2, at the 97th percentile. Family history is positive for diabetes mellitus requiring insulin, in father (diagnosed at 11 years) and paternal grandmother and T2DM in paternal aunt. Laboratory evaluation was negative for all 5 antibodies (GAD, IA-2, Anti-islet cell antibody, Zinc Transporter 8 and Insulin antibodies) and revealed an insulin level of 15.9 uIU/mL (RR: <2.0-13.0) and C peptide: 2.3 ng/mL (RR: 1.1-4.4). Lacking diagnostic criteria for T1DM or T2DM, genetic testing was performed. Patient tested heterozygous for mutations in 3 genes known to cause MODY: GCK [(c.350 G>T p. (G117V)], ABCC8 [(c.2270 C>G p.(T757R)], and HNF1B [(c.68A>G p.(K23R)], all variant of uncertain significance. Over an 8-month period, patient's weight decreased from 98 lbs. (44.9 kg) to 90 lbs. (41.1 kg) after meeting with our dietician and implementing healthy dietary changes, and his beta cell function markers improved from diagnosis: Fasting insulin (4.5 uIU/mL), C peptide (1.3 ng/mL), and glucose 119 mg/dL; Hemoglobin A1C remained relatively stable at 6.1%. A kidney ultrasound was normal. No medical intervention were started yet, and patient is being monitored clinically and biochemically every 3-4 months. Discussion: Clinical monitoring over time, genetic testing in the parents, are critical in this patient’s long-term treatment plan and prognosis. To our knowledge, this may be the first case of diabetes mellitus in a pediatric patient, positive for mutations in 3 different genes known to cause MODY. South Texas has one of the highest incidences of T2DM in the USA. In addition to screening for genetic forms of diabetes, in patients with negative T1DM antibodies and atypical phenotype for T2DM, we should consider genetic screening in mildly obese pediatric and young adult patients without significant acanthosis nigricans, who were already diagnosed as T2DM. Presentation: 6/1/2024

IDF21-0348 Incidence and risk of diabetic retinopathy in Emirati patients with maturity onset diabetes of the young (MODY)

Background: Diabetic retinopathy (DR) is a potentially sight-threatening complication of diabetes mellitus. The incidence and associated risk factors of DR has been studied in primary forms of diabetes but little is known with regards to maturity onset diabetes of the young (MODY), particularly in Middle Eastern populations Aim: We aimed to study the incidence of DR in Emirati patients with MODY and to identify clinical and biochemical risk factors associated with its occurrence. Method: Patients with diabetes mellitus underwent digital retinal photography at Imperial College London Diabetes Centre, United Arab Emirates (UAE). Retinal photographs were graded according to the NHS Diabetic Eye Screening Programme for severity of DR and presence or absence of maculopathy. Forty-eight patients highly suspected to have MODY were tested for mutations in all known monogenic diabetes genes using targeted next generation sequencing. Clinical and biochemical parameters were reviewed. Results: Pathogenic MODY mutations were identified in a total of 30 cases, with HNF1A, GCK, HNF4A, HNF1B, and CEL in 50%, 26.7%, 16.7%, 3.3% and 3.3%, respectively. Retinal disease of any grade was found in 26.7% (n=8) of individuals with a genetic diagnosis of MODY, with 75% (n=6) of HNF1A-MODY patients having background (n=4), proliferative (n=1), or stable-proliferative DR (n=1), and 25% (n=2) of HNF4A-MODY patients having background (n=1) or stable-proliferative (n=1) retinopathy. Maculopathy occurred in half (50%) of the HNF1A-MODY cases and all (100%) with HNF4A-MODY. Overall, the incidence rate of any degree of DR in patients with MODY was 880 (270-1490) cases per 10,000 person-years. Significant differences were found in univariate analysis in mean duration of diabetes (14.2±5.3 vs 5.4±6.3years, p=0.002), HbA1c (9.5±1.8% vs 7.1±1.3%, p=<0.001), total cholesterol (TC) (5.3±1.7 vs 4.1±1.0mmol/L, p=0.030), and triglycerides (1.8±1.1 vs 1.0±0.6mmol/L, p=0.018) between individuals with any degree of retinopathy and those without retinal disease. Treatment modality was significantly different in cases with and without any retinopathy (p=0.001), with 50% vs 9.1% receiving insulin. No significant difference in age at onset of diabetes (p=0.640), LDL (p=0.225), albumin-creatinine ratio (p=0.208) were observed. Mean age at examination, blood pressure (BP), estimated glomerular filtration rate, and BMI in individuals with or without retinopathy were 32.2±9.9 vs 19.9±10.9years, 114.5±9.8/69.4±7.4 vs 112.9±12.1/67.1±10.5mmHg, 122±31.6 vs 120.3±25mL/min/1.73m2, 24.1±2.4 vs 22.5±5.3kg/m2, respectively. In multivariate Cox regression incorporating TC:HDL ratio, systolic BP and HbA1c, increased TC:HDL was independently associated with significantly increased hazard of any degree of retinopathy (HR 3.96 (1.08-14.5)). Discussion: The incidence rate of any degree of retinopathy in Emirati patients with primarily HNF1A and HNF4A MODY appears increased in comparison to recently published incidence rates for Type 2 Diabetes (200 to 300 per 10,000 person-years) and comparable with rates reported in Type 1 Diabetes (500 to 660 cases per 10,000 person-years). The high incidence of retinal disease in HNF1A MODY highlights the importance of retinal screening from the time of diagnosis, along with early identification of potential MODY cases in order to optimise blood glucose quickly and effectively.

When do we need to suspect maturity onset diabetes of the young in patients with type 2 diabetes mellitus?

Maturity onset diabetes of the young (MODY) patients have clinical heterogeneity as shown by many studies. Thus, often it is misdiagnosed to type 1 or type 2 diabetes(T2DM). The aim of this study is to evaluate MODY mutations in adult T2DM patients suspicious in terms of MODY, and to show clinical and laboratory differences between these two situations. In this study, we analyzed 72 type 2 diabetic patients and their relatives (35F/37M) who had been suspected for MODY and referred to genetic department for mutation analysis. The gene mutations for MODY have been assessed in the laboratory of Marmara University genetics. Totally 67 (32F/35M; median age 36.1) diabetic patients were analyzed for 7 MODY mutations. Twelve patients who have uncertain mutation (VUS) were excluded from study for further evaluation. MODY(+) (n:30) patients and T2DM patients (n:25) were compared for clinical and laboratory parameters. In MODY(+) subjects, mutations in GCK (MODY 2) (n:12; 40%) were the most common followed by HNF4A (MODY 1) (n:4; 13.3%). Diabetes diagnosis age was younger in MODY(+) group but not statistically significant. Sixty-six percent of MODY(+) subjects had diabetes history at 3-consecutive generations in their family compared with 28% of T2DM patients statistically significant (p:0.006). Gender, BMI, C-peptide, HbA1c, lipid parameters, creatinine, GFR, microalbuminuria, vitamin D and calcium were not statistically different between the groups. According to present study results, MODY mutation positivity is most probable in young autoantibody (-) diabetic patients diagnosed before 30 years of age, who have first degree family history of diabetes.

A decision algorithm to identify patients with high probability of monogenic diabetes due to HNF1A mutations

PurposeTo investigate the utility of biomarkers of maturity-onset diabetes of the young (MODY), high-sensitivity C-reactive protein (hsCRP), and 1,5-anhydroglucitol (1,5-AG) in conjunction with other clinical and laboratory features to improve diagnostic accuracy and provide a diagnostic algorithm for HNF1A MODY.MethodsWe examined 77 patients with HNF1A MODY, 88 with GCK MODY mutations, 99 with type 1 diabetes, and 92 with type 2 diabetes. In addition to 1,5-AG and hsCRP, we considered body mass index (BMI), fasting glucose, and fasting serum C-peptide as potential biomarkers. Logistic regression and receiver operating characteristic curves were used in marker evaluation.ResultsConcentration of hsCRP was lowest in HNF1A MODY (0.51 mg/l) and highest in type 2 diabetes (1.33 mg/l). The level of 1,5-AG was lowest in type 1 diabetes and HNF1A MODY, 3.8 and 4.7 μg/ml, respectively, and highest (11.2 μg/ml) in GCK MODY. In the diagnostic algorithm, we first excluded patients with type 1 diabetes based on low C-peptide (C-statistic 0.98) before using high BMI and C-peptide to identify type 2 diabetes patients (C-statistic 0.92). Finally, 1,5-AG and hsCRP in conjunction yielded a C-statistic of 0.86 in discriminating HNF1A from GCK MODY. We correctly classified 92.9% of patients with type 1 diabetes, 84.8% with type 2 diabetes, 64.9% HNF1A MODY, and 52.3% GCK MODY patients.ConclusionsPlasma 1,5-AG and serum hsCRP do not discriminate sufficiently HNF1A MODY from common diabetes types, but could be potentially useful in prioritizing Sanger sequencing of HNF1A gene.

Genetic characterization of suspected MODY patients in Tunisia by targeted next-generation sequencing.

Maturity Onset Diabetes of the Young (MODY) is a monogenic form of diabetes with autosomal dominant inheritance pattern. The diagnosis of MODY and its subtypes is based on genetic testing. Our aim was investigating MODY by means of next-generation sequencing in the Tunisian population. We performed a targeted sequencing of 27 genes known to cause monogenic diabetes in 11 phenotypically suspected Tunisian patients. We retained genetic variants passing filters of frequency in public databases as well as their probable effects on protein structures and functions evaluated by bioinformatics prediction tools. Five heterozygous variants were found in four patients. They include two mutations in HNF1A and GCK that are the causative genes of the two most prevalent MODY subtypes described in the literature. Other possible mutations, including novel frameshift and splice-site variants were identified in ABCC8 gene. Our study is the first to investigate the clinical application of targeted next-generation sequencing for the diagnosis of MODY in Africa. The combination of this approach with a filtering/prioritization strategy made a step towards the identification of MODY mutations in the Tunisian population.

Maturity-onset diabetes of the young as a model for elucidating the multifactorial origin of type 2 diabetes mellitus.

Maturity‐onset diabetes of the young (MODY) is a form of diabetes classically characterized as having autosomal dominant inheritance, onset before the age of 25 years in at least one family member and partly preserved pancreatic β‐cell function. The 14 responsible genes are reported to be MODY type 1~14, of which MODY 2 and 3 might be the most common forms. Although MODY is currently classified as diabetes of a single gene defect, it has become clear that mutations in rare MODYs, such as MODY 5 and MODY 6, have small mutagenic effects and low penetrance. In addition, as there are differences in the clinical phenotypes caused by the same mutation even in the same family, other phenotypic modifying factors are thought to exist; MODY could well have characteristics of type 2 diabetes mellitus, which is of multifactorial origin. Here, we outline the effects of genetic and environmental factors on the known phenotypes of MODY, focusing mainly on the examples of MODY 5 and 6, which have low penetrance, as suggestive models for elucidating the multifactorial origin of type 2 diabetes mellitus.

Maturity-Onset Diabetes of the Young: An Overview with Focus on the Middle East.

Today, there are more than 32 million patients with diabetes in the Middle East (ME), the number is expected to double by 2040. In contrast to Europe and North America and despite the high prevalence of diabetes in ME, epidemiological data about incident and types of diabetes in the region is very limited. Maturity-onset diabetes of the young (MODY) is a subtype of monogenic diabetes representing 2-5% of all diabetes patients. The disease is autosomal dominant mode of inheritance characterized by β-cell malfunction below the age of 35 years. To date, there are 15 different MODY forms that have been identified; each has a distinct genetic etiology. It is very common that MODY is misdiagnosed between with type 1 or type 2 diabetes. Hence, accurate genetic diagnosis is crucial to individualize the treatment and to improve glycaemia control. New technologies such as next-generation sequencing (NGS) offer an excellent alternative to screen and identify causative MODY mutations. In this review, we summarize the main clinical and genetic characteristics for each MODY form. In addition, we shed light on MODY studies that have been executed in the ME region.

Whole-exome sequencing for mutation detection in pediatric disorders of insulin secretion: Maturity onset diabetes of the young and congenital hyperinsulinism.

To assess the utility of whole-exome sequencing (WES) for mutation detection in maturity-onset diabetes of the young (MODY) and congenital hyperinsulinism (CHI). MODY and CHI are the two commonest monogenic disorders of glucose-regulated insulin secretion in childhood, with 13 causative genes known for MODY and 10 causative genes identified for CHI. The large number of potential genes makes comprehensive screening using traditional methods expensive and time-consuming. Ten subjects with MODY and five with CHI with known mutations underwent WES using two different exome capture kits (Nimblegen SeqCap EZ Human v3.0 Exome Enrichment Kit, Nextera Rapid Capture Exome Kit). Analysis was blinded to previously identified mutations, and included assessment for large deletions. The target capture of five exome capture technologies was also analyzed using sequencing data from >2800 unrelated samples. Four of five MODY mutations were identified using Nimblegen (including a large deletion in HNF1B). Although targeted, one mutation (in INS) had insufficient coverage for detection. Eleven of eleven mutations (six MODY, five CHI) were identified using Nextera Rapid (including the previously missed mutation). On reconciliation, all mutations concorded with previous data and no additional variants in MODY genes were detected. There were marked differences in the performance of the capture technologies. WES can be useful for screening for MODY/CHI mutations, detecting both point mutations and large deletions. However, capture technologies require careful selection.

Quantitative Evaluation of Serum Proteins Uncovers a Protein Signature Related to Maturity-Onset Diabetes of the Young (MODY).

Maturity-onset diabetes of the young (MODY) is an inherited monogenic type of diabetes. Genetic mutations in MODY often cause nonsynonymous changes that directly lead to the functional distortion of proteins and the pathological consequences. Herein, we proposed that the inherited mutations found in a MODY family could cause a disturbance of protein abundance, specifically in serum. The serum samples were collected from a Uyghur MODY family through three generations, and the serum proteins after depletion treatment were examined by quantitative proteomics to characterize the MODY-related serum proteins followed by verification using target quantification of proteomics. A total of 32 serum proteins were preliminarily identified as the MODY-related. Further verification test toward the individual samples demonstrated the 12 candidates with the significantly different abundance in the MODY patients. A comparison of the 12 proteins among the sera of type 1 diabetes, type 2 diabetes, MODY, and healthy subjects was conducted and revealed a protein signature related with MODY composed of the serum proteins such as SERPINA7, APOC4, LPA, C6, and F5.

The Common p.R114W HNF4A Mutation Causes a Distinct Clinical Subtype of Monogenic Diabetes.

HNF4A mutations cause increased birth weight, transient neonatal hypoglycemia, and maturity onset diabetes of the young (MODY). The most frequently reported HNF4A mutation is p.R114W (previously p.R127W), but functional studies have shown inconsistent results; there is a lack of cosegregation in some pedigrees and an unexpectedly high frequency in public variant databases. We confirm that p.R114W is a pathogenic mutation with an odds ratio of 30.4 (95% CI 9.79-125, P = 2 × 10(-21)) for diabetes in our MODY cohort compared with control subjects. p.R114W heterozygotes did not have the increased birth weight of patients with other HNF4A mutations (3,476 g vs. 4,147 g, P = 0.0004), and fewer patients responded to sulfonylurea treatment (48% vs. 73%, P = 0.038). p.R114W has reduced penetrance; only 54% of heterozygotes developed diabetes by age 30 years compared with 71% for other HNF4A mutations. We redefine p.R114W as a pathogenic mutation that causes a distinct clinical subtype of HNF4A MODY with reduced penetrance, reduced sensitivity to sulfonylurea treatment, and no effect on birth weight. This has implications for diabetes treatment, management of pregnancy, and predictive testing of at-risk relatives. The increasing availability of large-scale sequence data is likely to reveal similar examples of rare, low-penetrance MODY mutations.

Characteristics of maturity onset diabetes of the young in a large diabetes center.

Maturity onset diabetes of the young (MODY) is a monogenic form of diabetes caused by a mutation in a single gene, often not requiring insulin. The aim of this study was to estimate the frequency and clinical characteristics of MODY at the Barbara Davis Center. A total of 97 subjects with diabetes onset before age 25, a random C‐peptide ≥0.1 ng/mL, and negative for all diabetes autoantibodies (GADA, IA‐2, ZnT8, and IAA) were enrolled, after excluding 21 subjects with secondary diabetes or refusal to participate. Genetic testing for MODY 1–5 was performed through Athena Diagnostics, and all variants of unknown significance were further analyzed at Exeter, UK. A total of 22 subjects [20 (21%) when excluding two siblings] were found to have a mutation in hepatocyte nuclear factor 4A (n = 4), glucokinase (n = 8), or hepatocyte nuclear factor 1A (n = 10). Of these 22 subjects, 13 had mutations known to be pathogenic and 9 (41%) had novel mutations, predicted to be pathogenic. Only 1 of the 22 subjects had been given the appropriate MODY diagnosis prior to testing. Compared with MODY‐negative subjects, the MODY‐positive subjects had lower hemoglobin A1c level and no diabetic ketoacidosis at onset; however, these characteristics are not specific for MODY. In summary, this study found a high frequency of MODY mutations with the majority of subjects clinically misdiagnosed. Clinicians should have a high index of suspicion for MODY in youth with antibody‐negative diabetes.

The clinical management of hyperglycemia in pregnancy complicated by maturity-onset diabetes of the young

Women with maturity-onset diabetes of the young (MODY) are often first identified and diagnosed with diabetes during pregnancy. Genetics and hyperglycemia play an important role in determining fetal size in MODY pregnancies. The principal objective of the current study is to determine the outcomes and clinical management of hyperglycemia in pregnancies complicated by glucokinase gene (GCK) and hepatocyte nuclear factor (HNF)-1α MODY mutations. A retrospective chart review of 37 women with a GCK/HNF-1α mutation was conducted. Data on variables such as birthweight, mode of delivery, and the treatment of hyperglycemia were available on 89 pregnancies. The birthweight in unaffected GCK offspring was significantly higher than in the affected GCK offspring (4.8 [4.1-5.2] kg vs 3.2 [3.1-3.7] kg; P = .01). Seven-point home blood glucose monitoring over a 7-day period in each trimester demonstrated higher fasting and postprandial glycemic excursions in the first trimester of GCK pregnancies when compared to HNF-1α pregnancies (fasting 104 [90-115] mg/dL vs 84 [77-88] mg/dL; P = .01 and postprandial 154 [135-196] mg/dL vs 111 [100-131] mg/dL; P = .04) despite insulin treatment. There was a higher percentage of miscarriages in the GCK group when compared to the HNF-1α MODY group (33.3% vs 14%; P = .07), which was similar to the background population. Insulin initiated at an early gestation appeared to lower the incidence of macrosomia in GCK unaffected offspring. Hyperglycemia in HNF-1α pregnancies is easily managed with current insulin protocols; in contrast, glycemic excursions are difficult to manage in GCK pregnancies. There was an increased percentage of miscarriages in GCK pregnancies highlighting the importance of a diagnosis of GCK-MODY in women prior to conception and the necessity for preconception care.

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.

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). 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. 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. 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.

Monogenic diabetes mellitus in Norway

Here, we review data on monogenic diabetes mellitus in Norway based on the Norwegian MODY Registry at Haukeland University Hospital, Bergen. This registry comprises established or suspected cases of maturity-onset diabetes of the young (MODY) referred to our laboratory for genetic testing. We also present data on neonatal diabetes, another group of monogenic diabetes. To date, we have genetically diagnosed nearly 500 MODY cases in Norway. Mutations in the HNF1A gene (MODY3) were detected in about 50% of families with clinical MODY. GCK-MODY (MODY2) was the second most prevalent type, but may be underreported. We have also found mutations in the monogenic genes ABCC8, CEL, HNF1B, HNF4A, INS, KCNJ11 and NEUROD1. Based on genetic screening in the Norwegian MODY Registry and HUNT2, we estimate the number of MODY cases in Norway to be at least 2500-5000. Founder effects may determine the geographical distribution of MODY mutations in Norway. The molecular genetic testing of MODY and neonatal diabetes is mandatory for correct diagnosis and prognosis as well as choice of therapy

Gestational Diabetes Mellitus: Primum Non Nocere

Maturity-onset diabetes of the young (MODY) encompasses a collection of distinct forms of diabetes, which are inherited in an autosomal-dominant mode from the maternal or paternal side of the family or occasionally occur as a de novo mutation. All the genes involved affect either β-cell sensing or insulin secretion (1). The clinical presentations of MODY are heterogeneous, reflecting the different gene mutations involved, and the glucose dysregulation observed ranges from a relatively innocent rise in the fasting glucose to frank diabetes with neurological involvement (2,3). An exact MODY prevalence within the general diabetes population has proven difficult to assess because of underrecognition and lack of routinely available and affordable diagnostic tools. A further confounder is that the reported regional prevalence of specific MODY mutations varies considerably (4). Conservative estimates suggest that between 0.14–1.8% of all cases of diabetes could be attributable to MODY (4). It is to be expected that among women screened for gestational diabetes mellitus (GDM) the prevalence of MODY will be higher, reflecting both the proportionately lower prevalence of type 2 diabetes in women of this age group and the probability that those with undiagnosed MODY will screen positive (5). From the few population studies reported, mutations in the hepatocyte nuclear factor 1 α ( HNF1a ) gene (MODY 3) and glucokinase ( GCK ) gene (MODY 2) account for the majority of cases (6). MODY 2 is characterized by its high penetrance, early onset, and lifelong fasting hyperglycemia. It is due to mutations in the pancreatic GCK gene, which acts as the β-cell glucose sensor, setting the glucose threshold at which amplification of insulin …

Probing the effect of MODY mutations near the co-activator-binding pocket of HNF4α

HNF4α (hepatocyte nuclear factor 4α) is a culprit gene product for a monogenic and dominantly inherited form of diabetes, referred to as MODY (maturity onset diabetes of the young). As a member of the NR (nuclear receptor) superfamily, HNF4α recruits transcriptional co-activators such as SRC-1α (steroid receptor co-activator-1α) and PGC-1α (peroxisome-proliferator-activated receptor γ co-activator-1α) through the LXXLL-binding motifs for its transactivation, and our recent crystal structures of the complex provided the molecular details and the mechanistic insights into these co-activator recruitments. Several mutations have been identified from the MODY patients and, among these, point mutations can be very instructive site-specific measures of protein function and structure. Thus, in the present study, we probed the functional effects of the two MODY point mutations (D206Y and M364R) found directly near the LXXLL motif-binding site by conducting a series of experiments on their structural integrity and specific functional roles such as overall transcription, ligand selectivity, target gene recognition and co-activator recruitment. While the D206Y mutation has a subtle effect, the M364R mutation significantly impaired the overall transactivation by HNF4α. These functional disruptions are mainly due to their reduced ability to recruit co-activators and lowered protein stability (only with M364R mutation), while their DNA-binding activities and ligand selectivities are preserved. These results confirmed our structural predictions and proved that MODY mutations are loss-of-function mutations leading to impaired β-cell function. These findings should help target selective residues for correcting mutational defects or modulating the overall activity of HNF4α as a means of therapeutic intervention.

Discovery of a Novel Site Regulating Glucokinase Activity following Characterization of a New Mutation Causing Hyperinsulinemic Hypoglycemia in Humans

Type 2 diabetes is a global problem, and current ineffective therapeutic strategies pave the way for novel treatments like small molecular activators targeting glucokinase (GCK). GCK activity is fundamental to beta cell and hepatocyte glucose metabolism, and heterozygous activating and inactivating GCK mutations cause hyperinsulinemic hypoglycemia (HH) and maturity onset diabetes of the young (MODY) respectively. Over 600 naturally occurring inactivating mutations have been reported, whereas only 13 activating mutations are documented to date. We report two novel GCK HH mutations (V389L and T103S) at residues where MODY mutations also occur (V389D and T103I). Using recombinant proteins with in vitro assays, we demonstrated that both HH mutants had a greater relative activity index than wild type (6.0 for V389L, 8.4 for T103S, and 1.0 for wild type). This was driven by an increased affinity for glucose (S(0.5), 3.3 ± 0.1 and 3.5 ± 0.1 mm, respectively) versus wild type (7.5 ± 0.1 mm). Correspondingly, the V389D and T103I MODY mutants had markedly reduced relative activity indexes (<0.1). T103I had an altered affinity for glucose (S(0.5), 24.9 ± 0.6 mm), whereas V389D also exhibited a reduced affinity for ATP and decreased catalysis rate (S(0.5), 78.6 ± 4.5 mm; ATP(K(m)), 1.5 ± 0.1 mm; K(cat), 10.3 ± 1.1s(-1)) compared with wild type (ATP(K(m)), 0.4 ± <0.1; K(cat), 62.9 ± 1.2). Both Thr-103 mutants showed reduced inhibition by the endogenous hepatic inhibitor glucokinase regulatory protein. Molecular modeling demonstrated that Thr-103 maps to the allosteric activator site, whereas Val-389 is located remotely to this position and all other previously reported activating mutations, highlighting α-helix 11 as a novel region regulating GCK activity. Our data suggest that pharmacological manipulation of GCK activity at locations distal from the allosteric activator site is possible.

New HNF-1α nonsense mutation causes maturity-onset diabetes of the young type 3

Epidemiological studies indicate that approximately 5% of people previously classified as type 2 diabetes mellitus carriers and 10% of those considered as type 1 are, in fact, carriers of maturity‐onset diabetes of the young (MODY), a subtype of non‐insulin‐dependent diabetes mellitus.1 This monogenic form of diabetes is characterized by early onset (usually under 25 years old), high penetrance and the autosomal dominant mode of inheritance.2,3 Six MODY genes have already been identified. The MODY 3 subtype, caused by mutations in the HNF‐1α (hepatocyte nuclear factor‐1 alpha) gene,4 is the most common Mendelian form of diabetes and it is found in more than 60% of the cases classified as MODY, accounting for 1–2% of all diabetic individuals.5 The diabetic phenotype of the carriers of this mutation is due to altered gene expression of pancreatic β‐cells, mainly of the genes encoding insulin, the glucose transporter Glut2, amino acid transporters and some mitochondrial enzymes.6,7 The identification of the MODY genes has important clinical implications for patients, and their correct diagnosis is essential for a more appropriate treatment of the disease. The aim of this study was to examine a family suspected of carrying a type of MODY diabetes, searching for mutations present in this syndrome and its correlation with the clinical aspects of the patients. This study received approval from the Ethics Committee of the Universidade Estadual de Ponta Grossa (COEP authorization no. 14/2009, protocol no. 00884/09) and signed consent was obtained from all patients. Three generations of a family from South Brazil with a history of progressive and early diabetes, characteristics of MODY 3,2,3,5,8 were analyzed. EDTA anticoagulant venous blood samples were collected from the patients and the isolated genomic DNA9 was used as template in a polymerase chain reaction. Because MODY 3 is the most commonly occurring form of the disease in Brazil,10 oligonucleotides were synthesized for the flanking regions (introns) of the 10 exons of HNF‐1α. The samples were subjected to electrophoresis and purified, and then submitted for automatic nucleotide sequencing. After nucleotide alignment, the presence of a mutation in exon 2 of the HNF1‐α gene was detected in some members of the family: the proband and her daughters (Figure 1). The transition of a guanine to an adenine nucleotide at position 339 of codon 113 (TGG→TGA) has generated a nonsense mutation in this position (W113X), not yet described in the literature, which inhibits the formation of a functional protein in the affected individuals. More than 120 mutations have already been identified in the HNF1‐α gene, e.g. missense, nonsense, frameshift and splice‐site MODY mutations, in all exons analyzed.11 The majority of mutations in the HNF‐1α protein lead to the formation of nonfunctional heterodimers with the product of the normal HNF‐1α allele, preventing them from binding to DNA. Figure 1 Heredogram representing three generations (Ι, ΙΙ and ΙΙΙ) of the family analyzed in this study. The arrow indicates the proband and the asterisks (*) represent the members examined in this work. All the affected members analyzed in this study showed hyperglycemia at young ages, and the proband, now 38 years old, already manifests impaired vision and microcirculation, characteristics of a progressive syndrome, such as MODY 3. Some reports may explain the precocious manifestation of the disease in individuals of this study. According to Harries et al.12 the age of MODY 3 diagnosis is determined, in part, by the location of the mutation; mutations in the proximal segment of the HNF‐1α gene should give rise to a more severe phenotype than mutations in the distal regions. Furthermore, the age at diagnosis of diabetes varies according to the type of the HNF‐1α mutations: the median age at diagnosis was lower in patients with truncating mutations than in those with missense mutations.13 Functionally, the HNF‐1α protein can be divided in three regions: amino‐terminal dimerization domain (amino acids 1–32), homeodomain binding domain (203–276) and transactivation carboxyl‐terminal domain (281–631).14 The mutations in this protein are more frequent in the homeodomain regions and in a near amino‐terminal region, between residues 91 and 185,15,16 in agreement with our findings (mutation at amino acid 113). This region is responsible for binding and specificity in the interaction with DNA.15,17 Studies indicated that suppression of HNF‐1α function affects β‐cell metabolism leading to MODY 318 and concluded that normal function of the HNF‐1α protein is required for correct transcription of the insulin gene.19 In conclusion, the data presented in this study describe a new mutation for MODY type 3 and suggest functional significance of this genetic alteration in the insulin secretion process, besides highlighting the diagnostic importance of this type of diabetes aiming the control and clinical follow up.

Examination of Rare Variants in HNF4α in European Americans withType 2 Diabetes

The hepatocyte nuclear factor 4-α (HNF4α) gene codes for a transcription factor which is responsible for regulating gene transcription in pancreatic beta cells, in addition to its primary role in hepatic gene regulation. Mutations in this gene can lead to maturity-onset diabetes of the young (MODY), an uncommon, autosomal dominant, non-insulin dependent form of diabetes. Mutations in HNF4α have been found in few individuals, and infrequently have they segregated completely with MODY in families. In addition, due to similarity of phenotypes, it is unclear what proportion of type 2 diabetes (T2DM) in the general population is due to MODY or HNF4α mutations specifically. In this study, 27 documented rare and common variants were genotyped in a European American population of 1270 T2DM cases and 1017 controls from review of databases and literature implicating HNF4α variants in MODY and T2DM. Seventeen variants were found to be monomorphic. Two cases and one control subject had one copy of a 6-bp P2 promoter deletion. The intron 1 variant (rs6103716; MAF = 0.31) was not significantly associated with disease status (p>0.8) and the missense variant Thr130Ile (rs1800961; MAF = 0.027) was also not significantly different between cases and controls (p>0.2), but showed a trend consistent with association with T2DM. Four variants were found to be rare as heterozygotes in small numbers of subjects. Since many variants were infrequent, a pooled chi-squared analysis of rare variants was used to assess the overall burden of variants between cases and controls. This analysis revealed no significant difference (P=0.22). We conclude there is little evidence to suggest that HNF4α variants contribute significantly to risk of T2DM in the general population, but a modest contribution cannot be excluded. In addition, the observation of some mutations in controls suggests they are not highly penetrant MODY-causing variants.

Paternally Inherited Proinsulin Mutations May Result in Earlier Onset of Monogenic Diabetes Mutation Identity Effect in Monogenic Diabetes

Mutations within the human proinsulin gene ( INS ) have been reported to cause neonatal, maturity onset diabetes of the young (MODY), and antibody-negative idiopathic type 1 diabetes (1–3). However, because the expression of maternally or paternally transmitted INS-IGF2 alleles is different as a result of selective methylation (imprinting) (4), we surmised that the effect of INS mutations may depend on the origin of the mutated allele. To verify this hypothesis, pairs comprising an affected child and parent carrying the same heterozygous INS mutation were studied. A literature search was performed and yielded eight relevant articles reporting heterozygous INS mutations in neonatal, MODY, or antibody-negative type 1 diabetes (supplementary Table 1, available in an online appendix at http://care.diabetesjournals.org/cgi/content/full/dc10-1142/DC1). We also included an unpublished case …