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1.  Activating germline mutations in STAT3 cause early-onset multi-organ autoimmune disease 
Nature genetics  2014;46(8):812-814.
Monogenic causes of autoimmunity give key insights to the complex regulation of the immune system. We report a new monogenic cause of autoimmunity resulting from de novo germline activating STAT3 mutations in 5 individuals with a spectrum of early-onset autoimmune disease including type 1 diabetes. These findings emphasise the critical role of STAT3 in autoimmune disease and contrast with the germline inactivating STAT3 mutations that result in Hyper IgE syndrome.
doi:10.1038/ng.3040
PMCID: PMC4129488  PMID: 25038750
2.  Phenotypic severity of homozygous GCK mutations causing neonatal or childhood-onset diabetes is primarily mediated through effects on protein stability 
Human molecular genetics  2014;23(24):6432-6440.
Mutations in glucokinase (GCK) cause a spectrum of glycemic disorders. Heterozygous loss-of-function mutations cause mild fasting hyperglycemia irrespective of mutation severity due to compensation from the unaffected allele. Conversely, homozygous loss-of-function mutations cause permanent neonatal diabetes requiring lifelong insulin treatment. This study aimed to determine the relationship between in vitro mutation severity and clinical phenotype in a large international case series of patients with homozygous GCK mutations. Clinical characteristics for 30 patients with diabetes due to homozygous GCK mutations (19 unique mutations, including 16 missense) were compiled and assigned a clinical severity grade (CSG) based on birth weight and age at diagnosis. The majority (28 of 30) of subjects were diagnosed before 9 months, with the remaining two at 9 and 15 years. These are the first two cases of a homozygous GCK mutation diagnosed outside infancy. Recombinant mutant GCK proteins were analyzed for kinetic and thermostability characteristics and assigned a relative activity index (RAI) or relative stability index (RSI) value. Six of 16 missense mutations exhibited severe kinetic defects (RAI ≤ 0.01). There was no correlation between CSG and RAI (r2 = 0.05, P = 0.39), indicating that kinetics alone did not explain the phenotype. Eighty percent of the remaining mutations showed reduced thermostability, the exceptions being the two later-onset mutations which exhibited increased thermostability. Comparison of CSG with RSI detected a highly significant correlation (r2 = 0.74, P = 0.002). We report the largest case series of homozygous GCK mutations to date and demonstrate that they can cause childhood-onset diabetes, with protein instability being the major determinant of mutation severity.
doi:10.1093/hmg/ddu360
PMCID: PMC4240195  PMID: 25015100
3.  Digenic heterozygous HNF1A and HNF4A mutations in two siblings with childhood-onset diabetes 
Pediatric diabetes  2013;14(7):535-538.
Monogenic diabetes due to mutations in the transcription factor genes HNF1A and HNF4A is characterized by islet cell antibody negative, familial diabetes with residual insulin secretion. We report two sisters with childhood onset diabetes who are both heterozygous for the most common mutation in each of two transcription factors, hepatocyte nuclear factor 1A (HNF1A) and hepatocyte nuclear factor 4A (HNF4A). The proband was diagnosed with diabetes at 7 years of age and treated with insulin for 4 years. Her genetic diagnosis resulted in transition to sulfonylureas for one and a half years before insulin therapy was re-initiated due to declining glycemic control. Her sister was diagnosed with diabetes at 14 years of age, treated initially with insulin but has been well controlled on oral sulfonylurea therapy for over two years. Both sisters inherited the HNF4A gene mutation R127W from their mother and the HNF1A gene mutation P291fsinsC (c.872dup) from their father. The father was diagnosed with diabetes at 45 years of age. Their brother is heterozygous for the HNF4A R127W mutation. Both the brother and mother have normal glucose tolerance at the ages of 16 and 46 years, respectively.
Digenic inheritance of HNF1A and HNF4A mutations is very rare and has only been reported in two families where conclusive evidence for the pathogenicity of their mutations was lacking. Follow-up studies in this family co-segregating the two most commonly reported HNF1A/HNF4A mutations will be informative for understanding the effect of digenic inheritance upon phenotypic severity and response to sulfonylurea therapy.
doi:10.1111/pedi.12018
PMCID: PMC4090307  PMID: 23551881
HNF1A; HNF4A; MODY; youth
4.  Neurogenin 3 is important but not essential for pancreatic islet development in humans 
Diabetologia  2014;57(11):2421-2424.
doi:10.1007/s00125-014-3349-y
PMCID: PMC4181041  PMID: 25120094
Diabetes; Enteric anendocrinosis; Islet development; Neonatal diabetes; Neurogenin 3
5.  Recessive mutations in a distal PTF1A enhancer cause isolated pancreatic agenesis 
Nature genetics  2013;46(1):61-64.
The contribution of cis-regulatory mutations to human disease remains poorly understood. Whole genome sequencing can identify all non-coding variants, yet discrimination of causal regulatory mutations represents a formidable challenge. We used epigenomic annotation in hESC-derived embryonic pancreatic progenitor cells to guide the interpretation of whole genome sequences from patients with isolated pancreatic agenesis. This uncovered six different recessive mutations in a previously uncharacterized ~400bp sequence located 25kb downstream of PTF1A (pancreas-specific transcription factor 1a) in ten families with pancreatic agenesis. We show that this region acts as a developmental enhancer of PTF1A and that the mutations abolish enhancer activity. These mutations are the most common cause of isolated pancreatic agenesis. Integrating genome sequencing and epigenomic annotation in a disease-relevant cell type can uncover novel non-coding elements underlying human development and disease.
doi:10.1038/ng.2826
PMCID: PMC4131753  PMID: 24212882
6.  Permanent Neonatal Diabetes Mellitus: Prevalence and Genetic Diagnosis in the SEARCH for Diabetes in Youth Study 
Pediatric diabetes  2012;14(3):174-180.
Background
Neonatal diabetes mellitus (NDM) is defined as diabetes with onset before 6 months of age. Nearly half of individuals with NDM are affected by permanent neonatal diabetes mellitus (PNDM). Mutations in KATP channel genes (KCNJ11, ABCC8) and the insulin gene (INS) are the most common causes of PNDM.
Objective
To estimate the prevalence of PNDM among SEARCH for Diabetes in Youth (SEARCH) study participants (2001-2008) and to identify the genetic mutations causing PNDM.
Methods
SEARCH is a multi-center population-based study of diabetes in youth < 20 years of age. Participants diagnosed with diabetes before 6 months of age were invited for genetic testing for mutations in the KCNJ11, ABCC8 and INS genes.
Results
Of the 15,829 SEARCH participants with diabetes, 39 were diagnosed before 6 months of age. Thirty five of them had PNDM (0.22% of all diabetes cases in SEARCH), 3 had transient neonatal diabetes that had remitted by 18 months and one was unknown. The majority of them (66.7%) had a clinical diagnosis of type1 diabetes by their health care provider. Population prevalence of PNDM in youth <20 years was estimated at 1 in 252,000. Seven participants underwent genetic testing; mutations causing PNDM were identified in five (71%), (two KCNJ11, three INS).
Conclusions
We report the first population-based frequency of PNDM in the US based on the frequency of PNDM in SEARCH. Patients with NDM are often misclassified as having type1 diabetes. Widespread education is essential to encourage appropriate genetic testing and treatment of NDM.
doi:10.1111/pedi.12003
PMCID: PMC4101463  PMID: 23050777
neonatal diabetes; KCNJ11; INS; ABCC8; infant
7.  Phenotypic severity of homozygous GCK mutations causing neonatal or childhood-onset diabetes is primarily mediated through effects on protein stability 
Human Molecular Genetics  2014;23(24):6432-6440.
Mutations in glucokinase (GCK) cause a spectrum of glycemic disorders. Heterozygous loss-of-function mutations cause mild fasting hyperglycemia irrespective of mutation severity due to compensation from the unaffected allele. Conversely, homozygous loss-of-function mutations cause permanent neonatal diabetes requiring lifelong insulin treatment. This study aimed to determine the relationship between in vitro mutation severity and clinical phenotype in a large international case series of patients with homozygous GCK mutations. Clinical characteristics for 30 patients with diabetes due to homozygous GCK mutations (19 unique mutations, including 16 missense) were compiled and assigned a clinical severity grade (CSG) based on birth weight and age at diagnosis. The majority (28 of 30) of subjects were diagnosed before 9 months, with the remaining two at 9 and 15 years. These are the first two cases of a homozygous GCK mutation diagnosed outside infancy. Recombinant mutant GCK proteins were analyzed for kinetic and thermostability characteristics and assigned a relative activity index (RAI) or relative stability index (RSI) value. Six of 16 missense mutations exhibited severe kinetic defects (RAI ≤ 0.01). There was no correlation between CSG and RAI (r2 = 0.05, P = 0.39), indicating that kinetics alone did not explain the phenotype. Eighty percent of the remaining mutations showed reduced thermostability, the exceptions being the two later-onset mutations which exhibited increased thermostability. Comparison of CSG with RSI detected a highly significant correlation (r2 = 0.74, P = 0.002). We report the largest case series of homozygous GCK mutations to date and demonstrate that they can cause childhood-onset diabetes, with protein instability being the major determinant of mutation severity.
doi:10.1093/hmg/ddu360
PMCID: PMC4240195  PMID: 25015100
8.  GATA6 haploinsufficiency causes pancreatic agenesis in humans 
Nature genetics  2011;44(1):20-22.
Understanding the regulation of pancreatic development is key for efforts to develop new regenerative therapeutic approaches for diabetes. Rare mutations in PDX1 and PTF1A can cause pancreatic agenesis, however, most instances of this disorder are of unknown origin. We report de novo heterozygous inactivating mutations in GATA6 in 15/27 (56%) individuals with pancreatic agenesis. These findings define the most common cause of human pancreatic agenesis and establish a key role for the transcription factor GATA6 in human pancreatic development.
doi:10.1038/ng.1035
PMCID: PMC4062962  PMID: 22158542
9.  A Combination of Nifedipine and OctreotideTreatment in an HyperinsulinemicHypoglycemic Infant 
Hyperinsulinemic hypoglycemia (HH) is the commonest cause of persistent hypoglycemia in the neonatal and infancy periods. Mutations in the ABCC8 and KCNJ11 genes, which encode subunits of the ATP-sensitive potassium channel in the pancreatic beta cell, are identified in approximately 50% of these patients. The first-line drug in the treatment of HH is diazoxide. Octreotide and glucagon can be used in patients who show no response to diazoxide. Nifedipine, a calcium-channel blocker, has been shown to be an effective treatment in a small number of patients with diazoxide-unresponsive HH. We report a HH patient with a homozygous ABCC8 mutation (p.W1339X) who underwent a near-total pancreatectomy at 2 months of age due to a lack of response to diazoxide and octreotide treatment. Severe hypoglycemic attacks continued following surgery, while the patient was being treated with octreotide. These attacks resolved when nifedipine was introduced. Whilst our patient responded well to nifedipine, the dosage could not be increased to 0.75 mg/kg/day due to development of hypotension, a reported side effect of this drug. Currently, our patient, now aged 4 years, is receiving a combination of nifedipine and octreotide treatment. He is under good control and shows no side effects. In conclusion, nifedipine treatment can be started in patients with HH who show a poor response to diazoxide and octreotide treatment.
doi:10.4274/jcrpe.1230
PMCID: PMC4141574  PMID: 24932607
Nifedipine; diazoxide; hypotension; hypoglycemia; Hyperinsulinism
10.  Pancreatic Endocrine and Exocrine Function in Children following Near-Total Pancreatectomy for Diffuse Congenital Hyperinsulinism 
PLoS ONE  2014;9(5):e98054.
Context
Congenital hyperinsulinism (CHI), the commonest cause of persistent hypoglycaemia, has two main histological subtypes: diffuse and focal. Diffuse CHI, if medically unresponsive, is managed with near-total pancreatectomy. Post-pancreatectomy, in addition to persistent hypoglycaemia, there is a very high risk of diabetes mellitus and pancreatic exocrine insufficiency.
Setting
International referral centre for the management of CHI.
Patients
Medically unresponsive diffuse CHI patients managed with near-total pancreatectomy between 1994 and 2012.
Intervention
Near-total pancreatectomy.
Main Outcome Measures
Persistent hypoglycaemia post near-total pancreatectomy, insulin-dependent diabetes mellitus, clinical and biochemical (faecal elastase 1) pancreatic exocrine insufficiency.
Results
Of more than 300 patients with CHI managed during this time period, 45 children had medically unresponsive diffuse disease and were managed with near-total pancreatectomy. After near-total pancreatectomy, 60% of children had persistent hypoglycaemia requiring medical interventions. The incidence of insulin dependent diabetes mellitus was 96% at 11 years after surgery. Thirty-two patients (72%) had biochemical evidence of severe pancreatic exocrine insufficiency (Faecal elastase 1<100 µg/g). Clinical exocrine insufficiency was observed in 22 (49%) patients. No statistically significant difference in weight and height standard deviation score (SDS) was found between untreated subclinical pancreatic exocrine insufficiency patients and treated clinical pancreatic exocrine insufficiency patients.
Conclusions
The outcome of diffuse CHI patients after near-total pancreatectomy is very unsatisfactory. The incidence of persistent hypoglycaemia and insulin-dependent diabetes mellitus is very high. The presence of clinical rather than biochemical pancreatic exocrine insufficiency should inform decisions about pancreatic enzyme supplementation.
doi:10.1371/journal.pone.0098054
PMCID: PMC4026387  PMID: 24840042
11.  GATA6 Mutations Cause a Broad Phenotypic Spectrum of Diabetes From Pancreatic Agenesis to Adult-Onset Diabetes Without Exocrine Insufficiency 
Diabetes  2013;62(3):993-997.
We recently reported de novo GATA6 mutations as the most common cause of pancreatic agenesis, accounting for 15 of 27 (56%) patients with insulin-treated neonatal diabetes and exocrine pancreatic insufficiency requiring enzyme replacement therapy. We investigated the role of GATA6 mutations in 171 subjects with neonatal diabetes of unknown genetic etiology from a cohort of 795 patients with neonatal diabetes. Mutations in known genes had been confirmed in 624 patients (including 15 GATA6 mutations). Sequencing of the remaining 171 patients identified nine new case subjects (24 of 795, 3%). Pancreatic agenesis was present in 21 case subjects (six new); two patients had permanent neonatal diabetes with no enzyme supplementation and one had transient neonatal diabetes. Four parents with heterozygous GATA6 mutations were diagnosed with diabetes outside the neonatal period (12–46 years). Subclinical exocrine insufficiency was demonstrated by low fecal elastase in three of four diabetic patients who did not receive enzyme supplementation. One parent with a mosaic mutation was not diabetic but had a heart malformation. Extrapancreatic features were observed in all 24 probands and three parents, with congenital heart defects most frequent (83%). Heterozygous GATA6 mutations cause a wide spectrum of diabetes manifestations, ranging from pancreatic agenesis to adult-onset diabetes with subclinical or no exocrine insufficiency.
doi:10.2337/db12-0885
PMCID: PMC3581234  PMID: 23223019
12.  Reclassification of Diabetes Etiology in a Family With Multiple Diabetes Phenotypes 
Background:
Maturity-onset diabetes of the young (MODY) is uncommon; however, accurate diagnosis facilitates personalized management and informs prognosis in probands and relatives.
Objective:
The objective of the study was to highlight that the appropriate use of genetic and nongenetic investigations leads to the correct classification of diabetes etiology.
Case Discussion:
A 30-year-old European female was diagnosed with insulin-treated gestational diabetes. She discontinued insulin after delivery; however, her fasting hyperglycemia persisted. β-Cell antibodies were negative and C-peptide was 0.79 nmol/L. Glucokinase (GCK)-MODY was suspected and confirmed by the identification of a GCK mutation (p.T206M).
Methods:
Systematic clinical and biochemical characterization and GCK mutational analysis were implemented to determine the diabetes etiology in five relatives. Functional characterization of GCK mutations was performed.
Results:
Identification of the p.T206M mutation in the proband's sister confirmed a diagnosis of GCK-MODY. Her daughter was diagnosed at 16 weeks with permanent neonatal diabetes (PNDM). Mutation analysis identified two GCK mutations that were inherited in trans-p. [(R43P);(T206M)], confirming a diagnosis of GCK-PNDM. Both mutations were shown to be kinetically inactivating. The proband's mother, other sister, and daughter all had a clinical diagnosis of type 1 diabetes, confirmed by undetectable C-peptide levels and β-cell antibody positivity. GCK mutations were not detected.
Conclusions:
Two previously misclassified family members were shown to have GCK-MODY, whereas another was shown to have GCK-PNDM. A diagnosis of type 1 diabetes was confirmed in three relatives. This family exemplifies the importance of careful phenotyping and systematic evaluation of relatives after discovering monogenic diabetes in an individual.
doi:10.1210/jc.2013-3641
PMCID: PMC4186945  PMID: 24606082
13.  The HNF4A R76W mutation causes atypical dominant Fanconi syndrome in addition to a β cell phenotype 
Journal of Medical Genetics  2013;51(3):165-169.
Background
Mutation specific effects in monogenic disorders are rare. We describe atypical Fanconi syndrome caused by a specific heterozygous mutation in HNF4A. Heterozygous HNF4A mutations cause a beta cell phenotype of neonatal hyperinsulinism with macrosomia and young onset diabetes. Autosomal dominant idiopathic Fanconi syndrome (a renal proximal tubulopathy) is described but no genetic cause has been defined.
Methods and Results
We report six patients heterozygous for the p.R76W HNF4A mutation who have Fanconi syndrome and nephrocalcinosis in addition to neonatal hyperinsulinism and macrosomia. All six displayed a novel phenotype of proximal tubulopathy, characterised by generalised aminoaciduria, low molecular weight proteinuria, glycosuria, hyperphosphaturia and hypouricaemia, and additional features not seen in Fanconi syndrome: nephrocalcinosis, renal impairment, hypercalciuria with relative hypocalcaemia, and hypermagnesaemia. This was mutation specific, with the renal phenotype not being seen in patients with other HNF4A mutations. In silico modelling shows the R76 residue is directly involved in DNA binding and the R76W mutation reduces DNA binding affinity. The target(s) selectively affected by altered DNA binding of R76W that results in Fanconi syndrome is not known.
Conclusions
The HNF4A R76W mutation is an unusual example of a mutation specific phenotype, with autosomal dominant atypical Fanconi syndrome in addition to the established beta cell phenotype.
doi:10.1136/jmedgenet-2013-102066
PMCID: PMC3932761  PMID: 24285859
Renal Medicine; Calcium and Bone; Clinical Genetics; Diabetes; Metabolic Disorders
15.  An in-frame deletion at the polymerase active site of POLD1 causes a multisystem disorder with lipodystrophy 
Nature genetics  2013;45(8):947-950.
DNA polymerase delta, whose catalytic subunit is encoded by POLD1, is responsible for lagging strand DNA synthesis during DNA replication1. It achieves this with high fidelity due to its intrinsic 3′ to 5′ exonuclease activity, which confers proofreading ability. Missense mutations in the exonuclease domain of POLD1 have recently been shown to predispose to colorectal and endometrial cancer2. Here we report a recurring heterozygous single amino acid deletion at the polymerase active site of POLD1 that abolishes DNA polymerase activity but only mildly impairs 3′ to 5′ exonuclease activity. This mutation causes a distinct multisystem disorder that includes subcutaneous lipodystrophy, deafness, mandibular hypoplasia and hypogonadism in males. This suggests that perturbation of function of the ubiquitously expressed POLD1 polymerase has surprisingly tissue-specific effects in man, and argues for an important role for POLD1 function in adipose tissue homeostasis.
doi:10.1038/ng.2670
PMCID: PMC3785143  PMID: 23770608
16.  Analysis of Transcription Factors Key for Mouse Pancreatic Development Establishes NKX2-2 and MNX1 Mutations as Causes of Neonatal Diabetes in Man 
Cell Metabolism  2014;19(1):146-154.
Summary
Understanding transcriptional regulation of pancreatic development is required to advance current efforts in developing beta cell replacement therapies for patients with diabetes. Current knowledge of key transcriptional regulators has predominantly come from mouse studies, with rare, naturally occurring mutations establishing their relevance in man. This study used a combination of homozygosity analysis and Sanger sequencing in 37 consanguineous patients with permanent neonatal diabetes to search for homozygous mutations in 29 transcription factor genes important for murine pancreatic development. We identified homozygous mutations in 7 different genes in 11 unrelated patients and show that NKX2-2 and MNX1 are etiological genes for neonatal diabetes, thus confirming their key role in development of the human pancreas. The similar phenotype of the patients with recessive mutations and mice with inactivation of a transcription factor gene support there being common steps critical for pancreatic development and validate the use of rodent models for beta cell development.
Graphical Abstract
Highlights
•Homozygous mutations in seven pancreatic transcription factors cause neonatal diabetes•Homozygous NKX2-2 and MNX1 mutations were found in five patients•Confirms NKX2-2 and MNX1 are critical for murine and human pancreas development•Similar phenotypes in mouse and man validate models for beta cell development
Analyzing a large collection of consanguineous patients with permanent neonatal diabetes, Flanagan et al. performed a comprehensive search for recessive mutations in transcription factors known to be critical for mouse pancreatic development. They identify seven pancreatic transcription factors that cause neonatal diabetes, including NKX2-2 and MNX1.
doi:10.1016/j.cmet.2013.11.021
PMCID: PMC3887257  PMID: 24411943
17.  tRNA Methyltransferase Homolog Gene TRMT10A Mutation in Young Onset Diabetes and Primary Microcephaly in Humans 
PLoS Genetics  2013;9(10):e1003888.
We describe a new syndrome of young onset diabetes, short stature and microcephaly with intellectual disability in a large consanguineous family with three affected children. Linkage analysis and whole exome sequencing were used to identify the causal nonsense mutation, which changed an arginine codon into a stop at position 127 of the tRNA methyltransferase homolog gene TRMT10A (also called RG9MTD2). TRMT10A mRNA and protein were absent in lymphoblasts from the affected siblings. TRMT10A is ubiquitously expressed but enriched in brain and pancreatic islets, consistent with the tissues affected in this syndrome. In situ hybridization studies showed that TRMT10A is expressed in human embryonic and fetal brain. TRMT10A is the mammalian ortholog of S. cerevisiae TRM10, previously shown to catalyze the methylation of guanine 9 (m1G9) in several tRNAs. Consistent with this putative function, in silico topology prediction indicated that TRMT10A has predominant nuclear localization, which we experimentally confirmed by immunofluorescence and confocal microscopy. TRMT10A localizes to the nucleolus of β- and non-β-cells, where tRNA modifications occur. TRMT10A silencing induces rat and human β-cell apoptosis. Taken together, we propose that TRMT10A deficiency negatively affects β-cell mass and the pool of neurons in the developing brain. This is the first study describing the impact of TRMT10A deficiency in mammals, highlighting a role in the pathogenesis of microcephaly and early onset diabetes. In light of the recent report that the type 2 diabetes candidate gene CDKAL1 is a tRNA methylthiotransferase, the findings in this family suggest broader relevance of tRNA methyltransferases in the pathogenesis of type 2 diabetes.
Author Summary
The inherited predisposition to type 2 diabetes is attributed to common variants in over 60 loci. Among these risk variants is CDKAL1, which has recently been shown to be a tRNA modifying enzyme (methylthiotransferase). Genetic variants of different severity can generate a spectrum of monogenic and polygenic forms of diabetes. Here we describe a new syndrome of young onset diabetes, short stature and microcephaly (small brain size) with intellectual disability in a large consanguineous family. By linkage analysis and whole exome sequencing we identified a nonsense mutation in TRMT10A, a gene that has hitherto not been studied in mammals. The yeast homolog TRM10 has been shown to be a tRNA modifying enzyme with methyltransferase activity. We demonstrate that TRMT10A mRNA and protein are absent in cells from the affected siblings. TRMT10A localizes to the nucleolus, where tRNA modifications occur. TRMT10A silencing induces cell death in insulin-producing pancreatic β-cells, suggesting that TRMT10A deficiency may reduce β-cell mass and the pool of neurons in the brain. This is the first study describing the impact of TRMT10A deficiency in man. Our findings may have broader relevance for the understanding of the pathogenesis of type 2 diabetes and microcephaly.
doi:10.1371/journal.pgen.1003888
PMCID: PMC3814312  PMID: 24204302
18.  Cross-sectional and longitudinal studies suggest pharmacological treatment used in patients with glucokinase mutations does not alter glycaemia 
Diabetologia  2013;57(1):54-56.
Aims/hypothesis
Heterozygous glucokinase (GCK) mutations cause mild, fasting hyperglycaemia from birth. Although patients are usually asymptomatic and have glycaemia within target ranges, some are put on pharmacological treatment. We aimed to investigate how many patients are on pharmacological treatment and the impact of treatment on glycaemic control.
Methods
Treatment details were ascertained for 799 patients with heterozygous GCK mutations. In a separate, longitudinal study, HbA1c was obtained for 16 consecutive patients receiving insulin (n = 10) or oral hypoglycaemic agents (OHAs) (n = 6) whilst on treatment, and again having discontinued treatment following a genetic diagnosis of GCK-MODY. For comparison, HbA1c before and after genetic testing was studied in a control group (n = 18) not receiving pharmacological therapy.
Results
At referral for genetic testing, 168/799 (21%) of patients were on pharmacological treatment (13.5% OHAs, 7.5% insulin). There was no difference in the HbA1c of these patients compared with those receiving no treatment(median [IQR]: 48 [43, 51] vs 46 [43, 50] mmol/mol, respectively; 6.5% [6.1%, 6.8%] vs 6.4% [6.1%, 6.7%]; p = 0.11). Following discontinuation of pharmacological treatment in 16 patients, HbA1c did not change. The mean change in HbA1c was −0.68 mmol/mol (95% CI: −2.97, 1.61) (−0.06% [95% CI: −0.27, 0.15]).
Conclusions/interpretation
Prior to a genetic diagnosis, 21% of patients were on pharmacological treatment. HbA1c was no higher than in untreated patients and did not change when therapy was discontinued, suggesting no impact on glycaemia. The lack of response to pharmacological therapy is likely to reflect the regulated hyperglycaemia seen in these patients owing to their glucose sensing defect and is an example of pharmacogenetics.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-013-3075-x) contains peer reviewed but unedited supplementary material, which is available to authorised users.
doi:10.1007/s00125-013-3075-x
PMCID: PMC3855531  PMID: 24092492
GCK mutation; Glucokinase; MODY; Pharmacogenetics; Treatment
21.  Diabetes Mellitus in Neonates and Infants: Genetic Heterogeneity, Clinical Approach to Diagnosis, and Therapeutic Options 
Hormone Research in Pædiatrics  2013;80(3):137-146.
Over the last decade, we have witnessed major advances in the understanding of the molecular basis of neonatal and infancy-onset diabetes. It is now widely accepted that diabetes presenting before 6 months of age is unlikely to be autoimmune type 1 diabetes. The vast majority of such patients will have a monogenic disorder responsible for the disease and, in some of them, also for a number of other associated extrapancreatic clinical features. Reaching a molecular diagnosis will have immediate clinical consequences for about half of affected patients, as identification of a mutation in either of the two genes encoding the ATP-sensitive potassium channel allows switching from insulin injections to oral sulphonylureas. It also facilitates genetic counselling within the affected families and predicts clinical prognosis. Importantly, monogenic diabetes seems not to be limited to the first 6 months but extends to some extent into the second half of the first year of life, when type 1 diabetes is the more common cause of diabetes. From a scientific perspective, the identification of novel genetic aetiologies has provided important new knowledge regarding the development and function of the human pancreas.
doi:10.1159/000354219
PMCID: PMC3884170  PMID: 24051999
Neonatal diabetes; Monogenic diabetes of infancy ; Permanent neonatal diabetes; Transient neonatal diabetes ; Type 1 diabetes

22.  Multiple type 2 diabetes susceptibility genes following genome-wide association scan in UK samples 
Science (New York, N.Y.)  2007;316(5829):1336-1341.
The molecular mechanisms involved in the development of type 2 diabetes are poorly understood. Starting from genome-wide genotype data for 1,924 diabetic cases and 2,938 population controls generated by the Wellcome Trust Case Control Consortium, we set out to detect replicated diabetes association signals through analysis of 3,757 additional cases and 5,346 controls, and by integration of our findings with equivalent data from other international consortia. We detected diabetes susceptibility loci in and around the genes CDKAL1, CDKN2A/CDKN2B and IGF2BP2 and confirmed the recently described associations at HHEX/IDE and SLC30A8. Our findings provide insights into the genetic architecture of type 2 diabetes, emphasizing the contribution of multiple variants of modest effect. The regions identified underscore the importance of pathways influencing pancreatic beta cell development and function in the etiology of type 2 diabetes.
doi:10.1126/science.1142364
PMCID: PMC3772310  PMID: 17463249
23.  Antenatal Diagnosis of Fetal Genotype Determines if Maternal Hyperglycemia Due to a Glucokinase Mutation Requires Treatment 
Diabetes Care  2012;35(9):1832-1834.
OBJECTIVE
In women with hyperglycemia due to heterozygous glucokinase (GCK) mutations, the fetal genotype determines its growth. If the fetus inherits the mutation, birth weight is normal when maternal hyperglycemia is not treated, whereas intensive treatment may adversely reduce fetal growth. However, fetal genotype is not usually known antenatally, making treatment decisions difficult.
HISTORY AND EXAMINATION
We report two women with gestational diabetes mellitus resulting from GCK mutations with hyperglycemia sufficient to merit treatment.
INVESTIGATION
In both women, DNA from chorionic villus sampling, performed after high-risk aneuploidy screening, showed the fetus had inherited the GCK mutation. Therefore, maternal hyperglycemia was not treated. Both offspring had a normal birth weight and no peripartum complications.
CONCLUSIONS
In pregnancies where the mother has hyperglycemia due to a GCK mutation, knowing the fetal GCK genotype guides the management of maternal hyperglycemia. Fetal genotyping should be performed when fetal DNA is available from invasive prenatal diagnostic testing.
doi:10.2337/dc12-0151
PMCID: PMC3425005  PMID: 22773699
24.  Insights Into the Pathogenicity of Rare Missense GCK Variants From the Identification and Functional Characterization of Compound Heterozygous and Double Mutations Inherited in Cis 
Diabetes Care  2012;35(7):1482-1484.
OBJECTIVE
To demonstrate the importance of using a combined genetic and functional approach to correctly interpret a genetic test for monogenic diabetes.
RESEARCH DESIGN AND METHODS
We identified three probands with a phenotype consistent with maturity-onset diabetes of the young (MODY) subtype GCK-MODY, in whom two potential pathogenic mutations were identified: [R43H/G68D], [E248 K/I225M], or [G261R/D217N]. Allele-specific PCR and cosegregation were used to determine phase. Single and double mutations were kinetically characterized.
RESULTS
The mutations occurred in cis (double mutants) in two probands and in trans in one proband. Functional studies of all double mutants revealed inactivating kinetics. The previously reported GCK-MODY mutations R43H and G68D were inherited from an affected father and unaffected mother, respectively. Both our functional and genetic studies support R43H as the cause of GCK-MODY and G68D as a neutral rare variant.
CONCLUSIONS
These data highlight the need for family/functional studies, even for previously reported pathogenic mutations.
doi:10.2337/dc11-2420
PMCID: PMC3379612  PMID: 22611063
25.  Use of HbA1c in the Identification of Patients with Hyperglycaemia Caused by a Glucokinase Mutation: Observational Case Control Studies 
PLoS ONE  2013;8(6):e65326.
Aims
HaemoglobinA1c (HbA1c) is recommended for diabetes diagnosis but fasting plasma glucose (FPG) has been useful for identifying patients with glucokinase (GCK) mutations which cause lifelong persistent fasting hyperglycaemia. We aimed to derive age-related HbA1c reference ranges for these patients to determine how well HbA1c can discriminate patients with a GCK mutation from unaffected family members and young-onset type 1 (T1D) and type 2 diabetes (T2D) and to investigate the proportion of GCK mutation carriers diagnosed with diabetes using HbA1c and/or FPG diagnostic criteria.
Methods
Individuals with inactivating GCK mutations (n = 129), familial controls (n = 100), T1D (n = 278) and T2D (n = 319) aged ≥18years were recruited. Receiver Operating Characteristic (ROC) analysis determined effectiveness of HbA1c and FPG to discriminate between groups.
Results
HbA1c reference ranges in subjects with GCK mutations were: 38–56 mmol/mol (5.6–7.3%) if aged ≤40years; 41–60 mmol/mol (5.9–7.6%) if >40years. All patients (123/123) with a GCK mutation were above the lower limit of the HbA1c age-appropriate reference ranges. 69% (31/99) of controls were below these lower limits. HbA1c was also effective in discriminating those with a GCK mutation from those with T1D/T2D. Using the upper limit of the age-appropriate reference ranges to discriminate those with a mutation from those with T1D/T2D correctly identified 97% of subjects with a mutation. The majority (438/597 (73%)) with other types of young-onset diabetes had an HbA1c above the upper limit of the age-appropriate GCK reference range. HbA1c ≥48 mmol/mol classified more people with GCK mutations as having diabetes than FPG ≥7 mmol/l (68% vs. 48%, p = 0.0009).
Conclusions
Current HbA1c diagnostic criteria increase diabetes diagnosis in patients with a GCK mutation. We have derived age-related HbA1c reference ranges that can be used for discriminating hyperglycaemia likely to be caused by a GCK mutation and aid identification of probands and family members for genetic testing.
doi:10.1371/journal.pone.0065326
PMCID: PMC3683003  PMID: 23799006

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