RESUMO
AIMS/HYPOTHESIS: MODY is believed to be caused by at least 13 different genes. Five rare mutations at the BLK locus, including only one non-synonymous p.A71T variant, were reported to segregate with diabetes in three MODY families. The p.A71T mutation was shown to abolish the enhancing effect of BLK on insulin content and secretion from pancreatic beta cell lines. Here, we reassessed the contribution of BLK to MODY and tested the effect of BLK-p.A71T on type 2 diabetes risk and variations in related traits. METHODS: BLK was sequenced in 64 unelucidated MODY samples. The BLK-p.A71T variant was genotyped in a French type 2 diabetes case-control study including 4,901 cases and 4,280 controls, and in the DESIR (Data from an Epidemiological Study on the Insulin Resistance Syndrome) and SUVIMAX (Supplementation en Vitamines et Mineraux Antioxydants) population-based cohorts (n = 6,905). The variant effects were assessed by logistic and linear regression models. RESULTS: No rare non-synonymous BLK mutations were found in the MODY patients. The BLK p.A71T mutation was present in 52 normoglycaemic individuals, making it very unlikely that this loss-of-function mutation causes highly penetrant MODY. We found a nominal association between this variant and increased type 2 diabetes risk, with an enrichment of the mutation in the obese diabetic patients, although no significant association with BMI was identified. CONCLUSIONS/INTERPRETATION: No mutation in BLK was found in our MODY cohort. From our findings, the BLK-p.A71T mutation may weakly influence type 2 diabetes risk in the context of obesity; however, this will require further validation.
Assuntos
Diabetes Mellitus Tipo 2/genética , Adolescente , Adulto , Criança , Diabetes Mellitus Tipo 2/epidemiologia , Feminino , Predisposição Genética para Doença/genética , Humanos , Masculino , Mutação , Adulto Jovem , Quinases da Família srcRESUMO
Maturity-onset diabetes of the young (MODY) is a subtype of non-insulin dependent diabetes mellitus, with early age of onset. MODY is genetically heterogeneous, associated with glucokinase mutations and a locus on chromosome 20q; in about 50% of cases, its genetic background is unknown. We have studied 12 families in which MODY is unlinked to either glucokinase or chromosome 20q markers, and find significant evidence for linkage with microsatellite markers on chromosome 12q, most likely within a 7 centimogran interval bracketed by D12S86 and D12S342. The disease was estimated to be linked to this chromosome region in approximately 50% of families in a heterogeneity analysis. These MODY patients exhibit major hyperglycaemia with a severe insulin secretory defect, suggesting that the causal gene is implicated in pancreatic beta-cell function.
Assuntos
Mapeamento Cromossômico , Cromossomos Humanos Par 12 , Diabetes Mellitus Tipo 2/genética , Adolescente , Adulto , Criança , Cromossomos Humanos Par 20 , DNA Satélite/genética , Feminino , Genes Dominantes , Ligação Genética , Marcadores Genéticos , Glucoquinase/genética , Humanos , Escore Lod , Masculino , LinhagemRESUMO
AIMS/HYPOTHESIS: An accurate molecular diagnosis of diabetes subtype confers clinical benefits; however, many individuals with monogenic diabetes remain undiagnosed. Biomarkers could help to prioritise patients for genetic investigation. We recently demonstrated that high-sensitivity C-reactive protein (hsCRP) levels are lower in UK patients with hepatocyte nuclear factor 1 alpha (HNF1A)-MODY than in other diabetes subtypes. In this large multi-centre study we aimed to assess the clinical validity of hsCRP as a diagnostic biomarker, examine the genotype-phenotype relationship and compare different hsCRP assays. METHODS: High-sensitivity CRP levels were analysed in individuals with HNF1A-MODY (n = 457), glucokinase (GCK)-MODY (n = 404), hepatocyte nuclear factor 4 alpha (HNF4A)-MODY (n = 54) and type 2 diabetes (n = 582) from seven European centres. Three common assays for hsCRP analysis were evaluated. We excluded 121 participants (8.1%) with hsCRP values >10 mg/l. The discriminative power of hsCRP with respect to diabetes aetiology was assessed by receiver operating characteristic curve-derived C-statistic. RESULTS: In all centres and irrespective of the assay method, meta-analysis confirmed significantly lower hsCRP levels in those with HNF1A-MODY than in those with other aetiologies (z score -21.8, p < 5 × 10(-105)). HNF1A-MODY cases with missense mutations had lower hsCRP levels than those with truncating mutations (0.03 vs 0.08 mg/l, p < 5 × 10(-5)). High-sensitivity CRP values between assays were strongly correlated (r (2) ≥ 0.91, p ≤ 1 × 10(-5)). Across the seven centres, the C-statistic for distinguishing HNF1A-MODY from young adult-onset type 2 diabetes ranged from 0.79 to 0.97, indicating high discriminative accuracy. CONCLUSIONS/INTERPRETATION: In the largest study to date, we have established that hsCRP is a clinically valid biomarker for HNF1A-MODY in European populations. Given the modest costs and wide availability, hsCRP could translate rapidly into clinical practice, considerably improving diagnosis rates in monogenic diabetes.
Assuntos
Proteína C-Reativa/análise , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/genética , Fator 1-alfa Nuclear de Hepatócito/genética , Técnicas de Diagnóstico Molecular , Adulto , Idade de Início , Biomarcadores/sangue , Diabetes Mellitus Tipo 2/diagnóstico , Europa (Continente) , Glucoquinase/química , Glucoquinase/genética , Fator 1-alfa Nuclear de Hepatócito/química , Fator 4 Nuclear de Hepatócito/química , Fator 4 Nuclear de Hepatócito/genética , Heterozigoto , Humanos , Metanálise como Assunto , Pessoa de Meia-Idade , Mutação , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Adulto JovemRESUMO
Congenital pancreatic hypoplasia is a rare cause of neonatal diabetes. We report on a series of three patients with pancreatic agenesis and congenital heart defects. All had abdominal scan evidence of pancreatic agenesis. In addition, Patient 1 had a ventricular septal defect, patent ductus arteriosus and pulmonary artery stenosis; Patient 2 had a truncus arteriosus and Patient 3 had tetralogy of Fallot. Two of the three patients have developmental delay. All three patients were isolated cases within the family. Investigations included sequencing of GCK, ABCC8, IPF1, NEUROD1, PTF1A, HNF1B, INS, ISL1, NGN3, HHEX, G6PC2, TCF7L2, SOX4, FOXP3 (Patients 1 and 2), GATA4 and KCNJ11 genes (all three patients), but no mutations were found. Genetic investigation to exclude paternal UPD 6, methylation aberrations and duplications of 6q24 was also negative in all three. 22q11 deletion was excluded in all three patients. Array CGH in Patient (1) showed a approximately 250 kb, paternally inherited duplication of chromosome 12q [arr cgh 12q24.33 (B35:CHR12:131808577-132057649++) pat], not found in the other two patients. Permanent neonatal diabetes mellitus due to pancreatic hypoplasia with congenital heart defects has been reported before and may represent a distinct condition. We discuss this rare association and review previously reported literature.
Assuntos
Deficiências do Desenvolvimento/diagnóstico , Deficiências do Desenvolvimento/genética , Cardiopatias Congênitas/diagnóstico , Cardiopatias Congênitas/genética , Pâncreas/anormalidades , Pancreatopatias/complicações , Pré-Escolar , Deleção Cromossômica , Cromossomos Humanos Par 12 , Cromossomos Humanos Par 22 , Hibridização Genômica Comparativa , Análise Mutacional de DNA , Deficiências do Desenvolvimento/complicações , Ecocardiografia/métodos , Feminino , Cardiopatias Congênitas/complicações , Humanos , Imageamento por Ressonância Magnética/métodos , Masculino , Pancreatopatias/diagnósticoRESUMO
The transcription factor 7-like 2 (TCF7L2) rs7903146 T allele was associated with type 2 diabetes (T2D) in most populations worldwide. In individuals of European descent, the association with T2D was recently found to be modulated by obesity status. However, further studies are necessary to clarify if whether interaction exists among subjects of non-European descent. In the present study, we analyzed the association of rs7903146 with T2D in 90 nonobese (Body Mass Index [BMI] <25kg/m(2)), 171 overweight (25≤BMI<30kg/m(2)) et 98 obese (BMI≥30kg/m(2)) individuals from Tunisia. The T allele was nominally associated with T2D in nonobese subjects (Odds Ratio [OR]=3.24 [1.10-9.53], P=0.021) whereas no effect was detected in overweight (P=0.3) and obese (P=0.22) individuals. Consequently, the same risk allele decreased susceptibility to obesity in T2D subjects (OR=0.47 [0.23-0.94], P=0.029) but not in normoglycemic controls (P=0.44). When analyzed all together, no allelic association was observed with T2D (P=0.20) whereas an artefactual association with decreased obesity (0.59 [0.38-0.90], P=0.013) was detected. As in Europeans, TCF7L2 is therefore not a risk factor for obesity in Tunisians, but its effect on T2D risk is modulated by obesity. In conclusion, the TCF7L2 rs7903146 T allele is nominally associated with T2D susceptibility in nonobese individuals from Tunisia.
Assuntos
Diabetes Mellitus Tipo 2/genética , Polimorfismo de Nucleotídeo Único , Proteína 2 Semelhante ao Fator 7 de Transcrição/genética , Adulto , Idoso , Alelos , Glicemia/análise , Índice de Massa Corporal , Comorbidade , Diabetes Mellitus Tipo 2/epidemiologia , Feminino , Frequência do Gene , Genótipo , Humanos , Peso Corporal Ideal , Masculino , Pessoa de Meia-Idade , Obesidade/epidemiologia , Sobrepeso/epidemiologia , Prevalência , Fatores de Risco , Proteína 2 Semelhante ao Fator 7 de Transcrição/fisiologia , Tunísia/epidemiologiaRESUMO
Activating mutations in genes KCNJ11 and ABCC8, which form the ATP-sensitive K+channel (K(ATP) channel), have been shown to cause transient or permanent neonatal diabetes. We describe here a rather different phenotype: two cases of adult diabetic patients-considered and treated as insulin-dependent diabetic patients since adolescence-who, in fact, turned out to be heterozygous for an ABCC8 mutation and able to successfully discontinue insulin while taking sulphonylurea treatment.
Assuntos
Transportadores de Cassetes de Ligação de ATP/genética , Autoanticorpos/sangue , Diabetes Mellitus Tipo 1/genética , Diabetes Mellitus Tipo 1/imunologia , Mutação , Canais de Potássio Corretores do Fluxo de Internalização/genética , Receptores de Droga/genética , Adolescente , Adulto , Feminino , Fator 1-alfa Nuclear de Hepatócito/genética , Humanos , Recém-Nascido , Doenças do Recém-Nascido/genética , Masculino , Pessoa de Meia-Idade , Receptores de SulfonilureiasRESUMO
Transglutaminase 2 (TG2 or TGM2) is a multi-functional enzyme which catalyzes transamidation reactions or acts as a G-protein in intracellular signalling. Tgm2-/- Mice lacking TG2 activity are glucose intolerant and show impairment of insulin secretion, suggesting an important physiological role for TG2 in the pancreatic beta cell. We have previously described a TGM2 heterozygous missense mutation ((c.998A>G, p.N333S) in a 14 year-old patient with insulin-treated diabetes and in his diabetic father. The aim of this study was to further investigate the role of TG2 in early-onset type 2 diabetes. We analysed the TGM2 gene in 205 patients with clinically defined Maturity Onset Diabetes of the Young (MODY) or early-onset type 2 diabetes. We found two novel heterozygous mutations (c.989T>G, p.M330R; c.992T>A, p.I331N), which were not detected in 300 normoglycemic controls. All mutations were in residues which are located close to the catalytic site and impaired transamidating activity in vitro. Gene expression of TGM family genes and localization of TG2 in normal human pancreas indicated that TG2 is the only transglutaminase significantly expressed in human pancreatic islet cells. We conclude that reduced TG2 activity can contribute to disorders of glucose metabolism possibly via an impairment of insulin secretion.
Assuntos
Diabetes Mellitus Tipo 2/genética , Proteínas de Ligação ao GTP/genética , Mutação de Sentido Incorreto , Transglutaminases/genética , Adolescente , Adulto , Idade de Início , Animais , Células COS , Chlorocebus aethiops , Heterozigoto , Humanos , Imuno-Histoquímica , Proteína 2 Glutamina gama-GlutamiltransferaseAssuntos
Diabetes Mellitus/congênito , Diabetes Mellitus/genética , Fator de Transcrição GATA6/genética , Cardiopatias Congênitas/genética , Mutação/genética , Pancreatopatias/congênito , Adolescente , Linhagem da Célula , Códon/genética , Diabetes Mellitus/patologia , Feminino , Humanos , Lactente , Recém-Nascido , Células Secretoras de Insulina/patologia , Pâncreas/anormalidades , Pancreatopatias/genéticaRESUMO
Missense and nonsense mutations in the glucokinase gene have recently been shown to result in maturity-onset diabetes of the young (MODY), a subtype of non-insulin-dependent diabetes mellitus with early age of onset. Glucokinase catalyzes the formation of glucose-6-phosphate and is involved in the regulation of insulin secretion and integration of hepatic intermediary metabolism. Nucleotide sequence analysis of exon 4 and its flanking intronic regions of the glucokinase gene, in four hyperglycemic individuals of a MODY family, revealed a deletion of 15 base pairs, which removed the t of the gt in the donor splice site of intron 4, and the following 14 base pairs. This deletion resulted in two aberrant transcripts, which were analyzed by reverse transcription of RNA from lymphoblastoid cells obtained from a diabetic patient. In one of the abnormal transcripts, exon 5 is missing, while in the other, the activation of a cryptic splice site leads to the removal of the last eight codons of exon 4. This intronic deletion in a donor splice site seems to cause a more severe form of glucose intolerance, compared with point mutations described in glucokinase. This might be due to a more pronounced effect on insulin secretion.
Assuntos
Diabetes Mellitus Tipo 2/genética , Glucoquinase/genética , Adulto , Sequência de Bases , Diabetes Mellitus Tipo 2/metabolismo , Feminino , Humanos , Íntrons , Linfócitos/enzimologia , Masculino , Dados de Sequência Molecular , Oligodesoxirribonucleotídeos/química , Splicing de RNA , RNA Mensageiro/genética , Deleção de SequênciaRESUMO
Transient (TNDM) and Permanent (PNDM) Neonatal Diabetes Mellitus are rare conditions occurring in about 1: 300,000 live births. In TNDM growth retarded infants develop diabetes in the first few weeks of life only to go into remission in a few months with possible relapse to a permanent diabetes state usually around adolescence or as adults. We believe that pancreatic dysfunction in this condition is maintained throughout life with relapse initiated at times of metabolic stress such as puberty or pregnancy. In PNDM, insulin secretory failure occurs in the late fetal or early postnatal period. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular levels. Among those, the very recently elucidated mutations in KCNJ11 and ABCC8 gene, encoding the Kir6.2 and SUR1 subunit of the pancreatic K(ATP) channel involved in regulation of insulin secretion accounts for one third to a half of the PNDM cases. Patients with TNDM are more likely to have intrauterine growth retardation and less likely to develop ketoacidosis than patients with PNDM. In TNDM, patients are younger at the diagnosis of diabetes and have lower initial insulin requirements. Considerable overlap occurs between the two groups, so that TNDM cannot be distinguished from PNDM based on clinical features. Very early onset diabetes mellitus seems to be unrelated to autoimmunity in most instances. Recurrent diabetes is common in patients with "transient" neonatal diabetes mellitus and, consequently, prolonged follow-up is imperative. Molecular analysis of chromosome 6 anomalies, the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1 provide a tool to identify transient from permanent neonatal diabetes mellitus in the neonatal period. This analysis also has potentially important therapeutic consequences leading to transfer some patients, those with mutations in KCNJ11 and ABCC8 from insulin therapy to sulfonylureas. Realizing how difficult it is to take care of a child of this age with diabetes mellitus should prompt clinicians to transfer these children to specialized centers. Insulin therapy and high caloric intake are the basis of the treatment. Insulin pump may offer an interesting therapeutic tool in this age group in experienced hands.
Assuntos
Diabetes Mellitus/etiologia , Transportadores de Cassetes de Ligação de ATP/genética , Cromossomos Humanos Par 6/genética , Diabetes Mellitus/diagnóstico , Diabetes Mellitus/terapia , Retardo do Crescimento Fetal , Aconselhamento Genético , Humanos , Hipoglicemiantes/uso terapêutico , Recém-Nascido , Insulina/uso terapêutico , Sistemas de Infusão de Insulina , Mutação , Canais de Potássio/genética , Canais de Potássio Corretores do Fluxo de Internalização/genética , Prognóstico , Receptores de Droga/genética , Receptores de SulfonilureiasRESUMO
Mutations in the glucokinase gene are a major cause of maturity-onset diabetes of the young. To evaluate the contribution of this gene to the development of late-onset NIDDM, linkage analyses between DNA polymorphisms at the glucokinase locus and NIDDM were performed in 79 multigenerational French families. In addition, all exons and the islet promoter region of glucokinase gene from 1 affected member from each family as well as from 17 unrelated women with previous gestational diabetes were amplified by polymerase chain reaction and screened for mutations by single-strand conformational polymorphism and DNA sequencing. Linkage of glucokinase and NIDDM was significantly rejected under all models tested. However, in 1 family, the lod score was 2.30, and we found a nucleotide substitution at the position -30 in the islet promoter region that cosegregated with diabetes. The proband of this family was a gestational diabetic individual. No other mutation in glucokinase was found in the 79 NIDDM families. We identified a missense mutation (TGG257-->CGG257) in exon 7 of glucokinase gene from 1 of 17 women with gestational diabetes, which was present in all diabetic members of her family. This family is likely to be a cryptic maturity-onset diabetes of the young, as 4 younger members, carrying this mutation, were subsequently found to be hyperglycemic. In conclusion, no evidence was obtained to incriminate glucokinase as a major gene for late age of onset NIDDM. Diabetic families with mutations in glucokinase must be carefully investigated, to differentiate cryptic maturity-onset diabetes of the young from late-onset NIDDM. Furthermore, pregnancy reveals diabetes in women carrying a glucokinase defect.
Assuntos
Diabetes Mellitus Tipo 2/genética , Ligação Genética , Glucoquinase/genética , Mutação , Adolescente , Adulto , Idoso , Sequência de Bases , Criança , DNA de Cadeia Simples/genética , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Dados de Sequência Molecular , Linhagem , Reação em Cadeia da Polimerase , Polimorfismo Genético , Gravidez , Gravidez em Diabéticas/genéticaRESUMO
Maturity-onset diabetes of the young (MODY) is a model for genetic studies of non-insulin-dependent diabetes mellitus. We have identified 15 MODY families in which diabetes is not the result of mutations in the glucokinase gene. This cohort of families will be useful for identifying other diabetes-susceptibility genes. Nine other candidate genes potentially implicated in insulin secretion or insulin action have been tested for linkage with MODY in these families, including glucokinase regulatory protein, hexokinase II, insulin receptor substrate 1, fatty acid-binding protein 2, glucagon-like peptide-1 receptor, apolipoprotein C-II, glycogen synthase, adenosine deaminase (a marker for the MODY gene on chromosome 20), and phosphoenolpyruvate carboxykinase. None of these loci showed evidence for linkage with MODY, implying that mutations in these genes do not make a major genetic contribution to the development of MODY. In addition to these linkage analyses, one or two affected subjects from each family were screened for the presence of the A to G mutation at nucleotide 3,243 of the mitochondrial tRNA(Leu(UUR)) gene. This mutation was not found in any of these subjects. Finally, we report the localization of the gene encoding the regulatory protein of glucokinase to chromosome 2, band p22.3 and the identification of a restriction fragment length polymorphism at this locus.
Assuntos
Diabetes Mellitus Tipo 2/genética , Adolescente , Adulto , Fatores Etários , Idoso , Sequência de Bases , Criança , Pré-Escolar , Mapeamento Cromossômico , Cromossomos Humanos Par 2 , Feminino , Ligação Genética , Glucoquinase/antagonistas & inibidores , Glucoquinase/genética , Humanos , Escore Lod , Masculino , Pessoa de Meia-Idade , Dados de Sequência Molecular , Mutação , Linhagem , Polimorfismo de Fragmento de Restrição , Proteínas/genética , RNA/genética , RNA Mitocondrial , RNA de Transferência de Leucina/genéticaRESUMO
The islet-1 (Isl-1) gene encodes a protein that binds to the enhancer region of the insulin gene. Isl-1 is a member of the LIM/homeodomain family of transcription factors. Because insulin deficiency, either relative or absolute, is a cardinal feature of non-insulin-dependent diabetes mellitus (NIDDM), this study addressed the question of whether mutations in genes that regulate insulin production could be involved. Rat Isl-1 was the first insulin enhancer binding protein to be isolated, and, in this study, the rat gene was used to isolate a partial human islet Isl-1 cDNA and subsequently to isolate genomic clones. A simple sequence repeat was found in the Isl-1 gene, and polymerase chain reaction amplification of this region of genomic DNA revealed 12 alleles in St. Louis African-Americans (het = 0.87), 14 alleles in black Nigerians (het = 0.89), 8 alleles in Japanese (het = 0.69), and 8 alleles in Caucasians (het = 0.81). Genetic linkage analysis uniquely placed Isl-1 on chromosome 5q (D5S395[12.8 cM]Isl-1 [11.6 cM]D5S407). The simple sequence repeat polymorphism at the Isl-1 locus was used to evaluate mutations in this gene as a possible contributor to the pathogenesis of NIDDM. Allelic frequencies did not differ between patients with NIDDM (n = 165) and nondiabetic control subjects (n = 163) in two black populations (St. Louis African-Americans and Nigerians). Linkage analyses in 15 nonglucokinase maturity-onset diabetes of the young pedigrees indicated that linkage could be rejected (LOD score < -3.0) over a distance of 15 cM.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Cromossomos Humanos Par 5 , Proteínas de Ligação a DNA/biossíntese , Diabetes Mellitus Tipo 2/genética , Elementos Facilitadores Genéticos , Genes Homeobox , Proteínas de Homeodomínio , Insulina/biossíntese , Proteínas do Tecido Nervoso , Fatores de Transcrição/biossíntese , Alelos , Povo Asiático/genética , Sequência de Bases , População Negra/genética , Mapeamento Cromossômico , Sequência Consenso , DNA/genética , Primers do DNA , Proteínas de Ligação a DNA/genética , Frequência do Gene , Ligação Genética , Marcadores Genéticos , Glucoquinase/genética , Humanos , Japão , Proteínas com Homeodomínio LIM , Escore Lod , Missouri , Dados de Sequência Molecular , Mutação , Nigéria , Linhagem , Reação em Cadeia da Polimerase/métodos , Polimorfismo Genético , Recombinação Genética , Sequências Repetitivas de Ácido Nucleico , Mapeamento por Restrição , Fatores de Transcrição/genética , População Branca/genéticaRESUMO
Activins are members of the transforming growth factor-beta superfamily. They have a wide range of biological effects on cell growth and differentiation. For transmembrane signaling, activins bind directly to activin receptor type 2A (ACVR2A) or 2B (ACVR2B). Transgenic and knock-out mice for the ACVR2B gene display various endocrine pancreas-related abnormalities, including islet hypoplasia and glucose intolerance, demonstrating the crucial role of ACVR2B in the regulation of pancreas development. We have thus examined the contribution of this factor to the development of mature-onset diabetes of the young (MODY) and type 2 diabetes. No evidence of linkage at the ACVR2B locus has been detected in MODY families with unknown etiology for diabetes or found in affected sib pairs from families with type 2 diabetes. Mutation screening of the coding sequence in MODY probands and in a family with severe type 2 diabetes, including a case of pancreatic agenesis, showed single nucleotide polymorphisms that did not cosegregate with MODY and were not associated with type 2 diabetes. Our results indicate that ACVR2B does not represent a common cause of either MODY or type 2 diabetes in the French Caucasian population.
Assuntos
Diabetes Mellitus Tipo 2/genética , Mutação , Receptores de Fatores de Crescimento/genética , Receptores de Activinas Tipo II , Éxons , França , Ligação Genética , Marcadores Genéticos , Genótipo , Humanos , Escore Lod , Linhagem , FenótipoRESUMO
The aim of our study was to investigate the relative prevalence of the different forms of diabetes in young adults and their respective clinical characteristics. Included were 51 nonobese patients (BMI < 27 kg/m2) with diabetes diagnosed before age 40, excluding typical IDDM. Each patient was subjected to screening for glucokinase gene (MODY2) and mitochondrial DNA (at nucleotide 3243) mutations, to HLA class II genotyping, and screening for the presence of islet cell antibodies (ICAs) and anti-GAD antibodies. Informative families were analyzed for linkage of diabetes to chromosome 12q (MODY3). Based on clinical criteria, patients were subdivided into MODY (n = 19) and non-MODY (n = 32). In the MODY group, we identified three patients with MODY2, one with the 3243 mitochondrial mutation, and another with autoimmune diabetes. One of the five MODY families available for linkage study was shown to have MODY3. In the non-MODY group, we found five patients with autoimmune diabetes and one with MODY2. No clinical parameter was helpful to classify patients in one of these subclasses of diabetes; however, the glucagon-stimulated C-peptide was useful to discriminate between MODY2 patients and the others. In conclusion, young and lean non-insulin-dependent diabetic patients constitute a very heterogeneous group, although they present similar clinical characteristics. The clinical distinction of MODY and non-MODY patients allows correct classification in, at most, 75% of the patients and thus is not sufficient to predict clinical course. However, immunological and genetic parameters allowed us to classify only 25% of the patients in specific diagnostic classes.
Assuntos
Cromossomos Humanos Par 12/genética , Diabetes Mellitus/classificação , Diabetes Mellitus/diagnóstico , Glucoquinase/genética , Mutação/genética , Adulto , Autoanticorpos/sangue , Estudos de Coortes , Diabetes Mellitus/genética , Diabetes Mellitus/imunologia , Família , Feminino , Ligação Genética , Marcadores Genéticos , Glutamato Descarboxilase/imunologia , Haplótipos/genética , Humanos , Ilhotas Pancreáticas/imunologia , Escore Lod , Masculino , Pessoa de Meia-Idade , Linhagem , Fenótipo , RNA de Transferência de Leucina/genéticaRESUMO
Mutations in genes encoding hepatocyte nuclear factor (HNF) are responsible for three of the five subtypes of maturity-onset diabetes of the young (MODY). This observation and molecular studies indicate that the HNF network is required for normal function of pancreatic beta-cells. This suggests that transcription factors involved in this complex network are candidates for genetic defects in MODY. Because the HNF-3beta gene is implicated in this network, we screened it for mutations in 21 probands of French ancestry with clinical diagnosis of MODY and early-onset type 2 diabetes. All of the five known MODY genes, HNF-4alpha, glucokinase, HNF-1alpha, HNF-1beta, and IPF1, were previously excluded as being the cause of diabetes in these families. By direct sequencing, we identified two transitions, an A-to-G at position -213 and a C-to-T at position -63 in the promoter and exon 1, respectively, of the HNF-3beta gene. A G-to-C transversion at position +32 in the intron 1 and three transitions, C-to-T at position 291, A-to-G at position 837, and G-to-A at position 1188 in the exon 3, resulting in noncoding mutations Ala97Ala, Gly279Gly, and Gln396Gln, respectively, were also identified. The allele frequencies were not significantly different between a control group and MODY probands. Familial segregation studies and linkage analysis showed that genetic variation in the HNF-3beta gene is unlikely to be the cause of early-onset type 2 diabetes in these Caucasian families.
Assuntos
Proteínas de Ligação a DNA/genética , Diabetes Mellitus Tipo 2/genética , Variação Genética/genética , Proteínas Nucleares/genética , Fatores de Transcrição , População Branca/genética , Adulto , Idade de Início , Sequência de Bases/genética , Diabetes Mellitus Tipo 2/epidemiologia , Feminino , França , Ligação Genética , Fator 3-beta Nuclear de Hepatócito , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
Non-insulin-dependent diabetes mellitus (NIDDM) is a clinically and genetically heterogeneous disorder. Maturity-onset diabetes of the young (MODY), an autosomal dominant form of NIDDM, has been used as a model for genetic studies of NIDDM. We recently reported linkage between markers on chromosome 12q and diabetes in 25% of our French MODY families. To evaluate if this gene is also implicated in late-onset NIDDM, we performed linkage studies between two markers of the MODY region and diabetes in 172 families with late-onset NIDDM. Both parametric and nonparametric methods were used in a total of 600 affected sib-pairs. Linkage was rejected in this population by all methods, implying that the MODY gene on chromosome 12q is not a major gene for late-onset NIDDM in this population. However, we cannot exclude a modifying role in a polygenic disorder or an important role in some families.
Assuntos
Mapeamento Cromossômico , Cromossomos Humanos Par 12 , Diabetes Mellitus Tipo 2/genética , Ligação Genética , Adulto , Fatores Etários , Idade de Início , Sequência de Bases , Primers do DNA , Diabetes Mellitus Tipo 2/fisiopatologia , Feminino , Genes Dominantes , Humanos , Masculino , Pessoa de Meia-Idade , Dados de Sequência Molecular , Pais , Reação em Cadeia da Polimerase , Caracteres SexuaisRESUMO
Mutations of the hepatocyte nuclear factor (HNF)-1alpha gene cause impaired insulin secretion and hyperglycemia in patients with maturity-onset diabetes of the young (MODY)3. Whether these mutations also affect glucose metabolism in tissues other than the beta-cell has not yet been documented. We therefore assessed, in five MODY3 patients and a dozen healthy control subjects, insulin secretion, oxidative and nonoxidative glucose disposal, and glucose production during a two-step hyperglycemic clamp and a euglycemic hyperinsulinemic (0.4 mU x kg(-1) x min(-1)) clamp. Compared with healthy control subjects, MODY3 patients had higher fasting plasma glucose (+100%) but similar rates of fasting glucose production and oxidation. Both the early and late phases of insulin secretion were virtually abolished during the hyperglycemic clamp, and glucose production was suppressed by only 43% in MODY3 patients vs. 100% in healthy control subjects. The rate of glucose infusion required to produce a 5 mmol/l increase above basal glycemia was reduced by 30%, net nonoxidative glucose disposal (which is equal to net glycogen deposition) was inhibited by 39%, and net carbohydrate oxidation during hyperglycemia was 25% lower in MODY3 patients compared with control subjects. Insulin-stimulated glucose utilization and oxidation measured during the hyperinsulinemic clamp (at approximately 200 pmol/l insulin) were identical in MODY3 patients and in healthy control subjects, indicating that peripheral insulin sensitivity was not altered. Suppression of endogenous glucose production was, however, mildly impaired. It is concluded that MODY3 patients have severely depressed glucose-induced insulin secretion. The development of hyperglycemia in these patients appears to be caused by a decreased stimulation of glucose utilization, oxidation, and nonoxidative glucose disposal as well as by a blunted suppression of endogenous glucose output. These phenomena are essentially secondary to insulinopenia, whereas insulin sensitivity remains intact.
Assuntos
Glicemia/metabolismo , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/metabolismo , Glucose/metabolismo , Mutação , Proteínas Nucleares , Fatores de Transcrição/genética , Adulto , Glicemia/efeitos dos fármacos , Proteínas de Ligação a DNA/genética , Ácidos Graxos não Esterificados/sangue , Feminino , Glucagon/sangue , Glucose/biossíntese , Técnica Clamp de Glucose , Fator 1 Nuclear de Hepatócito , Fator 1-alfa Nuclear de Hepatócito , Fator 1-beta Nuclear de Hepatócito , Humanos , Infusões Intravenosas , Insulina/administração & dosagem , Insulina/sangue , Insulina/farmacologia , Cinética , Masculino , Pessoa de Meia-Idade , Valores de Referência , Fatores de TempoRESUMO
Islet-1 (Isl-1) is a unique transcription factor that binds to the enhancer region of the insulin gene. To evaluate this gene in non-insulin-dependent diabetes mellitus (NIDDM), a full-length human Isl-1 cDNA was isolated and the genomic structure was characterized. The cDNA [2,395 bp plus additional poly(A) residues] contained an open reading frame from an initiator methionine at nucleotide 240 to an opal stop codon at nucleotide 1,286 (GenBank accession number UO7559), encoding a predicted protein of 349 amino acids (39 kDa). From their ends, 23 additional clones were sequenced, revealing 15 incomplete cDNAs and 8 intron-containing partially processed precursors. As determined by Northern blotting and reverse transcriptase-polymerase chain reaction analysis, Isl-1 was most abundantly expressed as a 2.4-kb mRNA in human islets, with a restricted pattern of expression in other adult human tissues. Analysis of genomic clones revealed that Isl-1 is encoded by six exons, varying in size from 168 bp (exon 5) to 1,230 bp (exon 6). Exons 2 and 3 each encode a LIM domain, while the homeodomain is completely contained within exon 4.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Proteínas de Ligação a DNA/genética , Diabetes Mellitus Tipo 2/genética , Genes Homeobox/genética , Proteínas de Homeodomínio , Proteínas do Tecido Nervoso , Sequência de Aminoácidos , Animais , Sequência de Bases , Northern Blotting , Mapeamento Cromossômico , Clonagem Molecular , Primers do DNA/genética , Éxons/genética , Genes , Humanos , Íntrons/genética , Proteínas com Homeodomínio LIM , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Ratos , Salmão/genética , Fatores de TranscriçãoRESUMO
In the search for diabetes genes, the combined approaches of positional cloning with random markers and subsequent evaluation of candidate genes mapping to areas of interest will be increasingly used. For islet candidate genes of unknown function, expressed trinucleotide (triplet) repeats represent a unique subset. It is unlikely that abnormal expansion of expressed islet triplet repeats would be a major cause of diabetes, yet the triplet repeats are frequently polymorphic and can thus be used to map the genes in the human genome. In this study, a human islet cDNA library was screened with (CGG)7 and (CAG)7, and 23 triplet repeats were isolated. Sequencing revealed four known and six novel islet genes containing 4-15 triplet repeats. The four known cDNAs included ferritin, the major iron-binding protein in cells; HSGSA2R, a full-length clone of the alpha-subunit of the G-regulatory protein; HUMSATB1A, a DNA-binding protein expressed predominantly in thymus; and HUMPPA-PRO, a ribosomal protein. The triplet repeats in ferritin and HUMPPAPRO were found to be monomorphic. Characterization of the six unique novel expressed islet triplet cDNAs revealed that they were 0.6-1.5 kb in size, contained 4-15 triplet repeats, and were expressed in islets and all other tissues examined. Four of the novel clones, CGG-isl 10, CGG-isl 11, CAG-isl 6, and CAG-isl 7, were mapped to human chromosomes 19, 16, 12, and 3, respectively, via somatic cell hybrids. One islet cDNA, CAG-isl 7, contained a repeat that was highly polymorphic, with 14 alleles (4-18 triplets) in African-Americans (heterozygosity = 0.86) and 6 alleles (heterozygosity = 0.77) in whites. Northern analysis indicated that the mRNA was abundant in pancreatic islets. A putative full-length clone contained an open reading frame encoding 213 amino acids with a variable number of alanines (4-18) within the COOH-terminal. The gene was uniquely mapped with odds > 1,000:1 on chromosome 3p in Centre d'Etude du Polymorphisme Humain pedigrees. There were no differences in CAG-isl 7 allele frequencies between African-American patients with NIDDM (n = 108) and control subjects (n = 116), nor was expansion above 18 repeats noted. Linkage analysis in 14 nonglucokinase maturity-onset diabetes of the young pedigrees showed a cumulative logarithm of odds score of -33.19 at theta = 0.00. Abnormal expansion was not observed in 20 IDDM patients with one NIDDM parent. While these data suggest no major role for CAG-isl 7 in diabetes, at least four of the six novel islet triplet genes are coexpressed in pancreatic islets and neural tissue, and these genes can now be considered as candidates for diabetes and/or neuropsychiatric diseases.