RESUMO
AIMS/HYPOTHESIS: MODY can be wrongly diagnosed as type 1 diabetes in children. We aimed to find the prevalence of MODY in a nationwide population-based registry of childhood diabetes. METHODS: Using next-generation sequencing, we screened the HNF1A, HNF4A, HNF1B, GCK and INS genes in all 469 children (12.1%) negative for both GAD and IA-2 autoantibodies and 469 antibody-positive matched controls selected from the Norwegian Childhood Diabetes Registry (3882 children). Variants were classified using clinical diagnostic criteria for pathogenicity ranging from class 1 (neutral) to class 5 (pathogenic). RESULTS: We identified 58 rare exonic and splice variants in cases and controls. Among antibody-negative patients, 6.5% had genetic variants of classes 3-5 (vs 2.4% in controls; p = 0.002). For the stricter classification (classes 4 and 5), the corresponding number was 4.1% (vs 0.2% in controls; p = 1.6 × 10-5). HNF1A showed the strongest enrichment of class 3-5 variants, with 3.9% among antibody-negative patients (vs 0.4% in controls; p = 0.0002). Antibody-negative carriers of variants in class 3 had a similar phenotype to those carrying variants in classes 4 and 5. CONCLUSIONS/INTERPRETATION: This is the first study screening for MODY in all antibody-negative children in a nationwide population-based registry. Our results suggest that the prevalence of MODY in antibody-negative childhood diabetes may reach 6.5%. One-third of these MODY cases had not been recognised by clinicians. Since a precise diagnosis is important for treatment and genetic counselling, molecular screening of all antibody-negative children should be considered in routine diagnostics.
Assuntos
Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/imunologia , Sequenciamento de Nucleotídeos em Larga Escala , Adolescente , Anticorpos/metabolismo , Proteínas Reguladoras de Apoptose , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Proteínas de Ciclo Celular/genética , Criança , Pré-Escolar , Diabetes Mellitus Tipo 2/metabolismo , Feminino , Quinases do Centro Germinativo , Fator 1-alfa Nuclear de Hepatócito/genética , Fator 1-beta Nuclear de Hepatócito/genética , Fator 4 Nuclear de Hepatócito/genética , Proteínas de Homeodomínio/genética , Humanos , Lactente , Recém-Nascido , Lipase/genética , Masculino , Noruega , Fatores de Transcrição Box Pareados/genética , Canais de Potássio Corretores do Fluxo de Internalização/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Repressoras/genética , Receptores de Sulfonilureias/genética , Transativadores/genética , Quinases da Família src/genéticaRESUMO
Dysfunction of the exocrine pancreas is observed in diabetes, but links between concurrent exocrine and endocrine pancreatic disease and contributing genetic factors are poorly characterized. We studied two families with diabetes and exocrine pancreatic dysfunction by genetic, physiological and in vitro functional studies. A genome-wide screen in Family 1 linked diabetes to chromosome 9q34 (maximal lod score 5.07). Using fecal elastase deficiency as a marker of exocrine pancreatic dysfunction refined the critical chromosomal region to 1.16 Mb (maximal lod score 11.6). Here, we identified a single-base deletion in the variable number of tandem repeats (VNTR)-containing exon 11 of the carboxyl ester lipase (CEL) gene, a major component of pancreatic juice and responsible for the duodenal hydrolysis of cholesterol esters. Screening subjects with maturity-onset diabetes of the young identified Family 2, with another single-base deletion in CEL and a similar phenotype with beta-cell failure and pancreatic exocrine disease. The in vitro catalytic activities of wild-type and mutant CEL protein were comparable. The mutant enzyme was, however, less stable and secreted at a lower rate. Furthermore, we found some evidence for an association between common insertions in the CEL VNTR and exocrine dysfunction in a group of 182 unrelated subjects with diabetes (odds ratio 4.2 (1.6, 11.5)). Our findings link diabetes to the disrupted function of a lipase in the pancreatic acinar cells.
Assuntos
Diabetes Mellitus Tipo 2/genética , Lipase/genética , Repetições Minissatélites , Mutação , Pâncreas Exócrino/fisiopatologia , Adulto , Animais , Células CHO , Cricetinae , Cricetulus , Diabetes Mellitus Tipo 2/etiologia , Diabetes Mellitus Tipo 2/patologia , Feminino , Humanos , Células Secretoras de Insulina/patologia , Lipase/metabolismo , Masculino , Dados de Sequência Molecular , Linhagem , RNA Mensageiro/metabolismoRESUMO
Glucokinase is the predominant hexokinase expressed in hepatocytes and pancreatic ß-cells, with a pivotal role in regulating glucose-stimulated insulin secretion, illustrated by glucokinase gene mutations causing monogenic diabetes and congenital hyperinsulinemic hypoglycemia. A complex tissue-specific network of mechanisms regulates this enzyme, and a major unanswered question in glucokinase biology is how post-translational modifications control the function of the enzyme. Here, we show that the pancreatic isoform of human glucokinase is SUMOylated in vitro, using recombinant enzymes, and in insulin-secreting model cells. Three N-terminal lysines unique for the pancreatic isoform (Lys-12/Lys-13 and/or Lys-15) may represent one SUMOylation site, with an additional site (Lys-346) common for the pancreatic and the liver isoform. SUMO-1 and E2 overexpression stabilized preferentially the wild-type human pancreatic enzyme in MIN6 ß-cells, and SUMOylation increased the catalytic activity of recombinant human glucokinase in vitro and also of glucokinase in target cells. Small ubiquitin-like modifier conjugation represents a novel form of post-translational modification of the enzyme, and it may have an important regulatory function in pancreatic ß-cells.
Assuntos
Regulação Enzimológica da Expressão Gênica , Glucoquinase/química , Pâncreas/enzimologia , Sumoilação , Animais , Carboidratos/química , Catálise , Eletroforese em Gel Bidimensional/métodos , Células Secretoras de Insulina/citologia , Cinética , Fígado/enzimologia , Espectrometria de Massas/métodos , Camundongos , Mutação , Isoformas de Proteínas , Processamento de Proteína Pós-Traducional , Proteínas Recombinantes/químicaRESUMO
GCK-MODY, dominantly inherited mild fasting hyperglycemia, has been associated with >600 different mutations in the glucokinase (GK)-encoding gene (GCK). When expressed as recombinant pancreatic proteins, some mutations result in enzymes with normal/near-normal catalytic properties. The molecular mechanism(s) of GCK-MODY due to these mutations has remained elusive. Here, we aimed to explore the molecular mechanisms for two such catalytically 'normal' GCK mutations (S263P and G264S) in the F260-L270 loop of GK. When stably overexpressed in HEK293 cells and MIN6 ß-cells, the S263P- and G264S-encoded mutations generated misfolded proteins with an increased rate of degradation (S263P>G264S) by the protein quality control machinery, and a propensity to self-associate (G264S>S263P) and form dimers (SDS resistant) and aggregates (partly Triton X-100 insoluble), as determined by pulse-chase experiments and subcellular fractionation. Thus, the GCK-MODY mutations S263P and G264S lead to protein misfolding causing destabilization, cellular dimerization/aggregation and enhanced rate of degradation. In silico predicted conformational changes of the F260-L270 loop structure are considered to mediate the dimerization of both mutant proteins by a domain swapping mechanism. Thus, similar properties may represent the molecular mechanisms for additional unexplained GCK-MODY mutations, and may also contribute to the disease mechanism in other previously characterized GCK-MODY inactivating mutations.
Assuntos
Diabetes Mellitus Tipo 2/genética , Glucoquinase , Proteínas Mutantes , Deficiências na Proteostase , Diabetes Mellitus Tipo 2/metabolismo , Glucoquinase/química , Glucoquinase/genética , Glucoquinase/metabolismo , Células HEK293 , Humanos , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Mutação , Octoxinol , Conformação Proteica , Dobramento de Proteína , Multimerização Proteica , Proteólise , Deficiências na Proteostase/genética , Deficiências na Proteostase/metabolismo , Reticulócitos/metabolismoRESUMO
We present a Norwegian family, followed since 1967, with a chromosome 6q24 duplication in two siblings with neonatal diabetes, in their non-diabetic father, and in a female (third generation) with adult-onset diabetes. The parents (first generation) were healthy and non-consanguineous. After a miscarriage, the couple had two infants with birth weights of 1780 and 1620 g, respectively, both of whom died on their second day of life. Patient I (male, weight 1840 g at term) had a blood glucose level of 33 mmol/L on day 6. He was treated with insulin for 3 months. In adult life he had permanent diabetes, treated with oral hypoglycemic agents. At 43 yr of age, there were no diabetic late complications. Patient II (female, birth weight 1440 g at term) had an increasing blood glucose of 55 mmol/L on day 13. She received insulin treatment for 12.5 months. Subsequently, she was successfully treated with sulfonylurea (tolbutamide) for 10 yr. At 11 yr of age, insulin was again considered necessary. At 40 yr of age, no diabetic late complications were detected. Patient III had a birth weight of 2630 g at term and no diabetic symptoms as a neonate. She had insulin-requiring diabetes from age 19. We conclude that (i) neonatal diabetes with chromosome 6q24 duplications may become a permanent disease in adult life; (ii) this chromosome anomaly may also be associated with adult-onset diabetes; (iii) sulfonylurea treatment may be attempted, and (iv) late diabetic complications may be absent, even after more than 40 yr.
Assuntos
Cromossomos Humanos Par 6/genética , Diabetes Mellitus/genética , Duplicação Gênica , Hipoglicemiantes/uso terapêutico , Compostos de Sulfonilureia/uso terapêutico , Adolescente , Adulto , Criança , Pré-Escolar , Diabetes Mellitus/tratamento farmacológico , Feminino , Seguimentos , Humanos , Lactente , Insulina/sangue , Insulina/uso terapêutico , Masculino , Metformina/uso terapêutico , Resultado do Tratamento , Adulto JovemRESUMO
A small-for-gestational age female infant presented with bilateral hypoplastic kidneys at 3 months of age. She developed chronic renal insufficiency. Insulin-requiring, non-autoimmune diabetes was documented at 6 years of age. She had mild steatosis and iron deposition in the liver, and mal-development of pancreas. Genetic studies revealed a heterozygous mutation (S148L) of the HNF1B gene, compatible with an HNF1B-MODY phenotype (MODY5). This is the first case of HNF1B-MODY reported from Turkey and represents a particularly severe phenotype of the disease.
Assuntos
Diabetes Mellitus Tipo 1/genética , Insuficiência Pancreática Exócrina/genética , Fator 1-beta Nuclear de Hepatócito/genética , Hepatopatias/genética , Mutação , Insuficiência Renal/genética , Sequência de Bases , Feminino , Humanos , Hipoglicemiantes , Lactente , Recém-Nascido , Recém-Nascido Pequeno para a Idade Gestacional , Insulina/uso terapêutico , Hepatopatias/patologia , Dados de Sequência Molecular , Índice de Gravidade de Doença , TurquiaRESUMO
One known genetic mechanism for transient neonatal diabetes is loss of methylation at 6q24. The etiology of prune belly sequence is unknown but a genetic defect, affecting the mesoderm from which the triad abdominal muscle hypoplasia, urinary tract abnormalities, and cryptorchidism develop, has been suggested. We investigated a family, including one twin, with transient neonatal diabetes and prune belly sequence. Autoantibody tests excluded type 1 diabetes. Microsatellite marker analysis confirmed the twins being monozygotic. We identified no mutations in ZFP57, KCNJ11, ABCC8, GCK, HNF1A, HNF1B, HNF3B, IPF1, PAX4, or ZIC3. The proband had loss of methylation at the 6q24 locus TNDM and also at the loci IGF2R, DIRAS3, and PEG1, while the other family members, including the healthy monozygotic twin, had normal findings. The loss of methylation on chromosome 6q24 and elsewhere may indicate a generalized maternal hypomethylation syndrome, which accounts for both transient neonatal diabetes and prune belly sequence.
Assuntos
DNA/genética , Diabetes Mellitus/genética , Doenças em Gêmeos/genética , Marcadores Genéticos/genética , Doenças do Recém-Nascido/genética , Mutação , Gêmeos Monozigóticos , Cromossomos Humanos Par 6 , Metilação de DNA , Análise Mutacional de DNA , Diabetes Mellitus/sangue , Humanos , Recém-Nascido , Masculino , Linhagem , Reação em Cadeia da PolimeraseRESUMO
BACKGROUND: Diabetes is classified as Type 1 diabetes, Type 2 diabetes, gestational diabetes and other types. Our goal was to provide an overview of new genetic knowledge of monogenic and type 2 diabetes. MATERIAL AND METHOD: The article is based on literature identified through a non-systematic search in PubMed and own experience concerning research in diabetes genetics and treatment of patients with monogenic diabetes. RESULTS: 18 genes have been found for which one single mutation may cause diabetes. The most common causes for such monogenic diabetes are mutations in the genes KCNJ11, ABCC8 and INS when the condition is diagnosed at the age 0 - 6 months, and in the genes HNF1A, GCK, HNF4A and HNF1B when the diagnosis is made later than six months of age. Genetic testing is appropriate in assessment of monogenic diabetes, because antidiabetic tablets rather that insulin injections can be used to treat patients with mutations in certain genes; i.e. KCNJ11, ABCC8, HNF1A and HNF4A. Genome-wide association studies have recently identified about 20 genetic variants that increase the risk of Type 2 diabetes, but which have a low predictive value for development of disease. How these genetic variants can cause Type 2 diabetes has not been assessed and clinical relevance remains to be shown. INTERPRETATION: So far, genetic findings only affect diagnosis and treatment of monogenic diabetes.
Assuntos
Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus/genética , Diabetes Mellitus/classificação , Diabetes Mellitus/congênito , Diabetes Mellitus Tipo 2/classificação , Diabetes Mellitus Tipo 2/tratamento farmacológico , Predisposição Genética para Doença , Testes Genéticos , Variação Genética , Fatores Nucleares de Hepatócito/genética , Humanos , Hipoglicemiantes/administração & dosagem , Lactente , Recém-Nascido , Mutação , Farmacogenética , Canais de Potássio Corretores do Fluxo de Internalização/genéticaRESUMO
BACKGROUND: Heterozygous activating mutations in KCNJ11, encoding the Kir6.2 subunit of the ATP-sensitive potassium (K(ATP)) channel, cause 30 to 58 percent of cases of diabetes diagnosed in patients under six months of age. Patients present with ketoacidosis or severe hyperglycemia and are treated with insulin. Diabetes results from impaired insulin secretion caused by a failure of the beta-cell K(ATP) channel to close in response to increased intracellular ATP. Sulfonylureas close the K(ATP) channel by an ATP-independent route. METHODS: We assessed glycemic control in 49 consecutive patients with Kir6.2 mutations who received appropriate doses of sulfonylureas and, in smaller subgroups, investigated the insulin secretory responses to intravenous and oral glucose, a mixed meal, and glucagon. The response of mutant K(ATP) channels to the sulfonylurea tolbutamide was assayed in xenopus oocytes. RESULTS: A total of 44 patients (90 percent) successfully discontinued insulin after receiving sulfonylureas. The extent of the tolbutamide blockade of K(ATP) channels in vitro reflected the response seen in patients. Glycated hemoglobin levels improved in all patients who switched to sulfonylurea therapy (from 8.1 percent before treatment to 6.4 percent after 12 weeks of treatment, P<0.001). Improved glycemic control was sustained at one year. Sulfonylurea treatment increased insulin secretion, which was more highly stimulated by oral glucose or a mixed meal than by intravenous glucose. Exogenous glucagon increased insulin secretion only in the presence of sulfonylureas. CONCLUSIONS: Sulfonylurea therapy is safe in the short term for patients with diabetes caused by KCNJ11 mutations and is probably more effective than insulin therapy. This pharmacogenetic response to sulfonylureas may result from the closing of mutant K(ATP) channels, thereby increasing insulin secretion in response to incretins and glucose metabolism. (ClinicalTrials.gov number, NCT00334711 [ClinicalTrials.gov].).
Assuntos
Diabetes Mellitus/tratamento farmacológico , Diabetes Mellitus/genética , Glibureto/uso terapêutico , Hipoglicemiantes/uso terapêutico , Canais de Potássio Corretores do Fluxo de Internalização/genética , Transportadores de Cassetes de Ligação de ATP/antagonistas & inibidores , Transportadores de Cassetes de Ligação de ATP/metabolismo , Estudos de Coortes , Diabetes Mellitus/metabolismo , Feminino , Glibureto/efeitos adversos , Hemoglobinas Glicadas/análise , Heterozigoto , Humanos , Hipoglicemiantes/efeitos adversos , Lactente , Recém-Nascido , Insulina/uso terapêutico , Células Secretoras de Insulina/efeitos dos fármacos , Células Secretoras de Insulina/metabolismo , Masculino , Mutação , Canais de Potássio/metabolismo , Canais de Potássio Corretores do Fluxo de Internalização/antagonistas & inibidores , Canais de Potássio Corretores do Fluxo de Internalização/metabolismo , Receptores de Droga/antagonistas & inibidores , Receptores de Droga/metabolismo , Compostos de Sulfonilureia/farmacologia , Receptores de Sulfonilureias , Tolbutamida/farmacologiaRESUMO
BACKGROUND: Mutations in genes of the mitogen-activated protein kinase (MAPK) cascade have recently been shown to cause several syndromes characterized by dysmorphic facial features, growth retardation, cognitive impairment, heart disease and cutaneous abnormalities. This signalling pathway involves RAS and RAF proteins, and is central in the regulation of normal growth and the development of cancer. MATERIAL AND METHODS: We have studied 23 Norwegian patients for whom there was a clinical suspicion of Costello, Noonan or cardio-facio-cutaneous syndrome. Patients suspected of having Noonan syndrome had previously tested negative for mutations in the tyrosine phosphatase gene PTPN11. The material was examined for mutations in the HRAS, KRAS, RAF1 and BRAF genes. Two patients are described to illustrate diagnostic challenges and the usefulness of genetic testing. RESULTS: Ten of 23 patients (43 %) had mutations affecting the RAS/MAPK signalling pathway. Mutations in HRAS were most common (five cases), while three patients had mutations in KRAS and two in RAF1. Spontaneous mutations were demonstrated in eight cases. Our data indicate an annual incidence of 1-2 new cases of congenital RAS/RAF mutations in Norway. INTERPRETATION: Upon clinical suspicion of syndromes of the RAS/MAPK signalling pathway, molecular genetic analyses may be essential for a correct diagnosis. Certain mutations are associated with an increased cancer risk, exemplifying that results of genetic laboratory testing may influence medical management.
Assuntos
Anormalidades Múltiplas/genética , Anormalidades Craniofaciais/genética , Sistema de Sinalização das MAP Quinases/genética , Quinases de Proteína Quinase Ativadas por Mitógeno/genética , Proteínas ras/genética , Adolescente , Adulto , Pré-Escolar , Síndrome de Costello/genética , Genes ras/genética , Técnicas Genéticas , Humanos , Lactente , Síndrome LEOPARD/genética , Masculino , Síndrome de Noonan/genética , Proteínas Proto-Oncogênicas A-raf/genética , Proteínas Proto-Oncogênicas B-raf/genética , SíndromeRESUMO
Both pancreatic volume reduction and lipomatosis have been observed in subjects with diabetes. The underlying molecular and pathological mechanisms are, however, poorly known, and it has been speculated that both features are secondary to diabetes. We have recently described pancreatic atrophy and lipomatosis in diabetic subjects of two Norwegian families with a novel syndrome of diabetes and exocrine pancreatic dysfunction caused by heterozygous carboxyl-ester lipase (CEL) mutations. To explore the early pathological events in this syndrome, we performed radiological examinations of the pancreas in nondiabetic mutation carriers with signs of exocrine dysfunction. In a case series study at a tertiary hospital, we evaluated 11 nondiabetic and mutation-positive children with fecal elastase deficiency and 11 age- and sex-matched control subjects using ultrasound and magnetic resonance imaging (MRI) to estimate pancreatic fat content. The pancreata of nondiabetic mutation carriers exhibited increased reflectivity on ultrasound and had MRI findings indicative of lipomatosis. Apparently, carriers of heterozygous CEL mutations accumulate fat in their pancreas before the anticipated development of diabetes. Our findings suggest that lipomatosis of the pancreas reflects early events involved in the pathogenesis of diabetes and exocrine pancreatic dysfunction syndrome.
Assuntos
Carboxilesterase/genética , Diabetes Mellitus/genética , Lipomatose/genética , Pâncreas/patologia , Pancreatopatias/genética , Adolescente , Adulto , Criança , Pré-Escolar , Diabetes Mellitus/diagnóstico por imagem , Diabetes Mellitus/patologia , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Mutação , Pâncreas/diagnóstico por imagem , Elastase Pancreática/deficiência , UltrassonografiaRESUMO
alpha-D-Glucose activates glucokinase (EC 2.7.1.1) on its binding to the active site by inducing a global hysteretic conformational change. Using intrinsic tryptophan fluorescence as a probe on the alpha-D-glucose induced conformational changes in the pancreatic isoform 1 of human glucokinase, key residues involved in the process were identified by site-directed mutagenesis. Single-site W-->F mutations enabled the assignment of the fluorescence enhancement (DeltaF/F(0)) mainly to W99 and W167 in flexible loop structures, but the biphasic time course of DeltaF/F(0) is variably influenced by all tryptophan residues. The human glucokinase-alpha-D-glucose association (K(d) = 4.8 +/- 0.1 mm at 25 degrees C) is driven by a favourable entropy change (DeltaS = 150 +/- 10 J.mol(-1).K(-1)). Although X-ray crystallographic studies have revealed the alpha-d-glucose binding residues in the closed state, the contact residues that make essential contributions to its binding to the super-open conformation remain unidentified. In the present study, we combined functional mutagenesis with structural dynamic analyses to identify residue contacts involved in the initial binding of alpha-d-glucose and conformational transitions. The mutations N204A, D205A or E256A/K in the L-domain resulted in enzyme forms that did not bind alpha-D-glucose at 200 mm and were essentially catalytically inactive. Our data support a molecular dynamic model in which a concerted binding of alpha-D-glucose to N204, N231 and E256 in the super-open conformation induces local torsional stresses at N204/D205 propagating towards a closed conformation, involving structural changes in the highly flexible interdomain connecting region II (R192-N204), helix 5 (V181-R191), helix 6 (D205-Y215) and the C-terminal helix 17 (R447-K460).
Assuntos
Glucoquinase/química , Glucoquinase/metabolismo , Glucose/metabolismo , Conformação Proteica , Sítios de Ligação , Ativação Enzimática , Glucoquinase/genética , Glucose/química , Humanos , Modelos Moleculares , Estrutura Molecular , Mutagênese Sítio-Dirigida , Mutação , Ligação Proteica , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Espectrometria de Fluorescência , Triptofano/química , Triptofano/metabolismoRESUMO
BACKGROUND: Maturity-onset diabetes of the young, type 2 (MODY2) is caused by mutations in the glucokinase gene (GCK). The aim of our study was to determine the prevalence of GCK mutations in the Norwegian MODY Registry and to delineate the clinical phenotype of identified GCK mutation carriers. METHODS: We screened 122 probands referred to the MODY Registry for mutations in GCK and studied extended families with MODY2. RESULTS: We found 2 novel (S76Y and N231S) and 13 previously reported (V62A, G72R, L146R, R191W, A208T, M210K, Y215X, M235T, R275C, E339G, R377C, S453L, and IVS5+1G>C) GCK mutations in 23 probands and in their 33 family members. The prevalence of MODY2 was 12% in the Norwegian MODY Registry. The subjects with GCK mutations had features of mild diabetes. Yet, 15 of 56 MODY2 subjects were treated with oral drugs or insulin. Three subjects had retinopathy and one had macrovascular disease. Also, a limited number of cases had elevated fasting serum triglyceride values. Moreover, two GCK mutation carriers were diagnosed with type 1 diabetes. CONCLUSIONS: According to our diagnostic screening of GCK in the MODY Registry, MODY2 is less prevalent than MODY3 in Norway but is likely to be underreported. Recognizing MODY2 in diabetic patients is important in order to prevent overtreatment. Finally, our study demonstrates the co-occurrence of MODY2 in families with type 1 or type 2 diabetes.
Assuntos
Diabetes Mellitus Tipo 2/genética , Glucoquinase/genética , Adolescente , Adulto , Criança , Pré-Escolar , Diabetes Mellitus Tipo 1/epidemiologia , Diabetes Mellitus Tipo 1/genética , Diabetes Mellitus Tipo 2/diagnóstico , Diabetes Mellitus Tipo 2/epidemiologia , Feminino , Humanos , Masculino , Noruega/epidemiologia , Linhagem , Prevalência , Sistema de Registros/estatística & dados numéricosRESUMO
Mutations in genes involved in Ras signalling cause Noonan syndrome and other disorders characterised by growth disturbances and variable neuro-cardio-facio-cutaneous features. We describe two sisters, 46 and 31 years old, who presented with dysmorphic features, hypotonia, feeding difficulties, retarded growth and psychomotor retardation early in life. The patients were initially diagnosed with Costello syndrome, and autosomal recessive inheritance was assumed. Remarkably, however, we identified a germline HRAS mutation (G12A) in one sister and a germline KRAS mutation (F156L) in her sibling. Both mutations had arisen de novo. The F156L mutant K-Ras protein accumulated in the active, guanosine triphosphate-bound conformation and affected downstream signalling. The patient harbouring this mutation was followed for three decades, and her cardiac hypertrophy gradually normalised. However, she developed severe epilepsy with hippocampal sclerosis and atrophy. The occurrence of distinct de novo mutations adds to variable expressivity and gonadal mosaicism as possible explanations of how an autosomal dominant disease may manifest as an apparently recessive condition.
Assuntos
Anormalidades Múltiplas/genética , Mutação em Linhagem Germinativa/genética , Transtornos do Crescimento/genética , Fenótipo , Proteínas Proto-Oncogênicas p21(ras)/genética , Proteínas Proto-Oncogênicas/genética , Proteínas ras/genética , Anormalidades Múltiplas/patologia , Adulto , Animais , Células COS , Chlorocebus aethiops , Análise Mutacional de DNA , Primers do DNA/genética , Face/anormalidades , Feminino , Genes Dominantes/genética , Transtornos do Crescimento/patologia , Cardiopatias Congênitas/genética , Hipocampo/anormalidades , Hipocampo/patologia , Humanos , Immunoblotting , Imageamento por Ressonância Magnética , Pessoa de Meia-Idade , Linhagem , Proteínas Proto-Oncogênicas/metabolismo , Transdução de Sinais/genética , Anormalidades da Pele/genética , Proteínas ras/metabolismoRESUMO
Variants in hepatocyte nuclear factor (HNF)-4alpha cause maturity-onset diabetes of the young, type 1 (MODY1) and may also be risk factors for type 2 diabetes. We sequenced the HNF4A gene of 95 MODY3-negative probands from the Norwegian MODY Registry. We found three novel coding variants in exon 8 of HNF4A: G326R, T339I, and W340X. In intron 7, we noted a single nucleotide polymorphism in the binding site of a previously published primer pair, which in some cases caused allelic drop out when amplifying exon 8. We also detected two novel sequence variants of the P2 promoter region, of which P2 -192C>G showed linkage with diabetes in two families (maximal logarithm of odds score of 3.1 and 0.8, respectively). This variant and a surrounding haplotype restricted by 3.7 Mb was also found in two Danish MODY pedigrees. The age of onset was higher in the P2 -192C>G carriers (median 45 years) compared with that reported for other MODY1 individuals. We could not support a biological role of the P2 promoter variant by in vitro transfection assays. In conclusion, we have identified three novel HNF4A mutations and a 3.7-Mb haplotype, including the HNF4A P2 promoter, which was linked with diabetes.
Assuntos
Diabetes Mellitus Tipo 2/genética , Haplótipos , Fator 4 Nuclear de Hepatócito/genética , Regiões Promotoras Genéticas/genética , População Branca/genética , Adulto , Idade de Início , Idoso , Animais , Linhagem Celular Tumoral , Dinamarca , Éxons , Vetores Genéticos/genética , Humanos , Íntrons , Pessoa de Meia-Idade , Noruega , Linhagem , Polimorfismo de Nucleotídeo Único , Sistema de Registros , TransfecçãoRESUMO
Glucokinase functions as a glucose sensor in pancreatic beta-cells and regulates hepatic glucose metabolism. A total of 83 probands were referred for a diagnostic screening of mutations in the glucokinase (GCK) gene. We found 11 different mutations (V62A, G72R, L146R, A208T, M210K, Y215X, S263P, E339G, R377C, S453L, and IVS5 + 1G>C) in 14 probands. Functional characterization of recombinant glutathionyl S-transferase-G72R glucokinase showed slightly increased activity, whereas S263P and G264S had near-normal activity. The other point mutations were inactivating. S263P showed marked thermal instability, whereas the stability of G72R and G264S differed only slightly from that of wild type. G72R and M210K did not respond to an allosteric glucokinase activator (GKA) or the hepatic glucokinase regulatory protein (GKRP). Mutation analysis of the role of glycine at position 72 by substituting E, F, K, M, S, or Q showed that G is unique since all these mutants had very low or no activity and were refractory to GKRP and GKA. Structural analysis provided plausible explanations for the drug resistance of G72R and M210K. Our study provides further evidence that protein instability in combination with loss of control by a putative endogenous activator and GKRP could be involved in the development of hyperglycemia in maturity-onset diabetes of the young, type 2. Furthermore, based on data obtained on G264S, we propose that other and still unknown mechanisms participate in the regulation of glucokinase.
Assuntos
Diabetes Mellitus Tipo 2/patologia , Glucoquinase/metabolismo , Proteínas Mutantes/metabolismo , Mutação , Sítios de Ligação , Glicemia/metabolismo , Proteínas de Transporte/metabolismo , Cristalografia por Raios X , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/prevenção & controle , Estabilidade Enzimática/efeitos dos fármacos , Testes Genéticos , Glucoquinase/química , Glucoquinase/genética , Glucose/farmacologia , Humanos , Hiperglicemia/enzimologia , Hiperglicemia/genética , Hiperglicemia/metabolismo , Cinética , Proteínas Mutantes/química , Ligação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de ProteínaRESUMO
Diabetes mellitus is a rare disorder during the first 2 years of life, amounting to about 3-5% of all cases diagnosed before the fifteenth birthday. However, in spite of low numerical values, this is an important diagnosis, since we are dealing with a vulnerable age group with major and special problems related to diagnosis, treatment and psychosocial follow-up. Efforts should be made to establish a molecular genetic diagnosis as early as possible (e.g. homozygous glucokinase deficiency, defects of the ATP-sensitive potassium channel, chromosome 6 imprinting abnormalities). This is particularly important, since patients with Kir6.2 and SUR1 defects can now be treated with oral sulfonylureas. Major advancements have been obtained and continue to be made with respect to diagnosis and classification. Differentiation between transient and permanent neonatal diabetes can only be done after long-term follow-up. Patients should be scrutinized for comorbidity (e.g. celiac disease, Wolcott-Rallison syndrome). Type 1 diabetes is probably the most prevalent subtype, particularly after the first year of life. Insulin treatment in infancy continues to represent major technical, medical and psychological challenges. Family support is mandatory and close attention should be paid to psychosocial issues.
Assuntos
Diabetes Mellitus/congênito , Diabetes Mellitus/terapia , Idade de Início , Criança , Pré-Escolar , Aberrações Cromossômicas , Cromossomos Humanos Par 6 , Diabetes Mellitus/epidemiologia , Diabetes Mellitus/genética , Diabetes Mellitus Tipo 1/congênito , Diabetes Mellitus Tipo 1/genética , Diabetes Mellitus Tipo 1/terapia , Impressão Genômica , Glucoquinase/genética , Humanos , Incidência , Lactente , Recém-Nascido , Canais KATP/genética , SíndromeAssuntos
Hipoglicemiantes/história , Insulina/história , Dinamarca , História do Século XIX , História do Século XX , Humanos , Noruega , OntárioRESUMO
Inappropriately elevated insulin secretion is the hallmark of persistent hyperinsulinemic hypoglycemia of infancy (PHHI), also denoted congenital hyperinsulinism. Causal mutations have been uncovered in genes coding for the beta-cell's ATP-sensitive potassium channel and the metabolic enzymes glucokinase and glutamate dehydrogenase. In addition, one hyperinsulinemic infant was recently found to have a mutation in the gene encoding short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD), an enzyme participating in mitochondrial fatty acid oxidation. We have studied a consanguineous family with severe neonatal hypoglycemia due to increased insulin levels and where well-established genetic causes of hyperinsulinism had been eliminated. A genome-wide, microsatellite-based screen for homozygous chromosomal segments was performed. Those regions that were inherited in accordance with the presupposed model were searched for mutations in genes encoding metabolic enzymes. A novel, homozygous deletion mutation was found in the gene coding for the SCHAD enzyme. The mutation affected RNA splicing and was predicted to lead to a protein lacking 30 amino acids. The observations at the molecular level were confirmed by demonstrating greatly reduced SCHAD activity in the patients' fibroblasts and enhanced levels of 3-hydroxybutyryl-carnitine in their blood plasma. Urine metabolite analysis showed that SCHAD deficiency resulted in specific excretion of 3-hydroxyglutaric acid. By the genetic explanation of our family's cases of severe hypoglycemia, it is now clear that recessively inherited SCHAD deficiency can result in PHHI. This finding suggests that mitochondrial fatty acid oxidation influences insulin secretion by a hitherto unknown mechanism.