Search PubMed⌕ Search

Biomedical subjects

P Froguel

Publications and source records attributed to P Froguel.

At least 181 records · Page 10Linked to original sources
PubMed1993

Familial hyperglycemia due to mutations in glucokinase. Definition of a subtype of diabetes mellitus.

BACKGROUND AND METHODS: Non-insulin-dependent diabetes mellitus (NIDDM) is a genetically heterogeneous disorder. Maturity-onset diabetes of the young, a form of NIDDM with an early age of onset and autosomal dominant inheritance, can result from mutations in glucokinase, a key enzyme of glucose metabolism in beta cells and the liver. We studied 32 French families with maturity-onset diabetes of the young as well as 21 families with late-onset NIDDM to determine the frequency and clinical features of mutations of glucokinase. Fasting plasma glucose concentrations and oral glucose-tolerance tests were used to determine metabolic status. DNA was isolated from lymphocytes, and DNA polymorphisms in the glucokinase gene were tested for linkage with diabetes. Individual exons of the glucokinase gene from one affected member in each family were amplified by the polymerase chain reaction and screened for mutations by analysis of the conformation-dependent polymorphisms of single-stranded DNA and by DNA sequencing. RESULTS: We found substantial evidence of linkage between the glucokinase locus and maturity-onset diabetes of the young but not between this locus and late-onset NIDDM: Sixteen mutations were identified in 18 of the 32 families with maturity-onset diabetes of the young, but none were found in families with late-onset NIDDM: They included 10 mutations that resulted in an amino acid substitution, 3 that resulted in the synthesis of a truncated protein, and 3 that affected RNA processing. The affected subjects with glucokinase mutations usually had mild hyperglycemia that began during childhood, whereas in subjects with maturity-onset diabetes of the young not due to glucokinase mutations, hyperglycemia usually appeared after puberty. CONCLUSIONS: Mutations in glucokinase are the primary cause of hyperglycemia in a substantial fraction of French patients with maturity-onset diabetes of the young and result in a relatively mild form of NIDDM that can be diagnosed in childhood.

Adult↗
PubMed1993

Glucokinase mutations associated with non-insulin-dependent (type 2) diabetes mellitus have decreased enzymatic activity: implications for structure/function relationships.

The glycolytic enzyme glucokinase plays an important role in the regulation of insulin secretion and recent studies have shown that mutations in the human glucokinase gene are a common cause of an autosomal dominant form of non-insulin-dependent (type 2) diabetes mellitus (NIDDM) that has an onset often during childhood. The majority of the mutations that have been identified are missense mutations that result in the synthesis of a glucokinase molecule with an altered amino acid sequence. To characterize the effect of these mutations on the catalytic properties of human beta-cell glucokinase, we have expressed native and mutant forms of this protein in Escherichia coli. All of the missense mutations show changes in enzyme activity including a decrease in Vmax and/or increase in Km for glucose. Using a model for the three-dimensional structure of human glucokinase based on the crystal structure of the related enzyme yeast hexokinase B, the mutations map primarily to two regions of the protein. One group of mutations is located in the active site cleft separating the two domains of the enzyme as well as in surface loops leading into this cleft. These mutations usually result in large reductions in enzyme activity. The second group of mutations is located far from the active site in a region that is predicted to undergo a substrate-induced conformational change that results in closure of the active site cleft. These mutations show a small approximately 2-fold reduction in Vmax and a 5- to 10-fold increase in Km for glucose. The characterization of mutations in glucokinase that are associated with a distinct and readily recognizable form of NIDDM has led to the identification of key amino acids involved in glucokinase catalysis and localized functionally important regions of the glucokinase molecule.

Amino Acid Sequence↗
PubMed1993

Susceptibility to insulin dependent diabetes mellitus maps to a 4.1 kb segment of DNA spanning the insulin gene and associated VNTR.

Recent studies have demonstrated that a locus at 11p15.5 confers susceptibility to insulin dependent diabetes mellitus (IDDM). This locus has been shown to lie within a 19 kb region. We present a detailed sequence comparison of the predominant haplotypes found in this region in a population of French Caucasian IDDM patients and controls. Identification of polymorphisms both associated and unassociated with IDDM has allowed us to define further the region of association to 4.1 kb. Ten polymorphisms within this region are in strong linkage disequilibrium with each other and extend across the insulin gene locus and the variable number tandem repeat (VNTR) situated immediately 5' to the insulin gene. These represent a set of candidate disease polymorphisms one or more of which may account for the susceptibility to IDDM.

Base Sequence↗
PubMed1993

Lipoprotein(a) in diabetic patients and normoglycemic relatives in familial NIDDM.

OBJECTIVE: To compare lipoprotein(a) levels in diabetic patients and normoglycemic relatives in familial NIDDM and to assess whether Lp(a) is a risk factor for myocardial infarction in this population. RESEARCH DESIGN AND METHODS: We compared 577 patients and 261 normoglycemic relatives from 189 NIDDM multiplex families with 49 unrelated healthy individuals. Of the 577, 23 patients with previously documented myocardial infarction were further analyzed as a separate group. RESULTS: Lp(a) concentrations in diabetic patients, normoglycemic relatives, and the control group were not significantly different. Variance of Lp(a) in a given individual could not be accounted for by any clinical or biological parameter, but was strongly related to the mean Lp(a) value in his or her family. Diabetic patients with previous myocardial infarction (and their relatives) had significantly higher levels of Lp(a) than patients without coronary heart disease complaints. CONCLUSIONS: Lp(a) concentration in familial NIDDM was not related to the degree of glucose intolerance, but presented a strong familial aggregation. High Lp(a) levels seem to be an independent risk factor for myocardial infarction in this NIDDM cohort.

Adult↗
PubMed1992

Primary pancreatic beta-cell secretory defect caused by mutations in glucokinase gene in kindreds of maturity onset diabetes of the young.

Maturity-onset diabetes of the young (MODY), characterised by non-insulin-dependent diabetes mellitus (NIDDM) with an early age of onset, is a genetically heterogeneous disorder. In most MODY kindreds described in France, chronic hyperglycaemia is caused by mutations in the gene encoding pancreatic beta-cell and liver glucokinase (GCK). We here report the beta-cell secretory profiles of nine patients from four GCK-linked MODY kindreds. First-phase insulin secretion assessed by an intravenous glucose test was comparable in patients and seven controls. However, beta-cell secretory response to continuous glucose stimulus during a hyperglycaemic glucose clamp was significantly reduced: mean plasma insulin values of 12 (SD 7) vs 40 (11) mU/l (p = 0.0001) and mean plasma C-peptide values 1.20 (0.30) vs 2.61 (0.37) (p = 0.0001). This secretory profile is different from those for NIDDM with late age of onset or MODY not linked to GCK. Fasting plasma insulin and C-peptide in patients were inappropriately low in relation to concomitant plasma glucose level. Furthermore, during a hyperinsulinaemic euglycaemic clamp, endogenous insulin secretion at euglycaemia (5 mmol/l) was suppressed in patients but not in controls. These results suggest that mutant GCK may lead to chronic hyperglycaemia by raising the threshold of circulating glucose level which induces insulin secretion. These data provide the first demonstration of a primary pancreatic secretory defect associated with a form of NIDDM.

Adolescent↗
PubMed1992

Human glucokinase gene: isolation, characterization, and identification of two missense mutations linked to early-onset non-insulin-dependent (type 2) diabetes mellitus.

DNA polymorphisms in the glucokinase gene have recently been shown to be tightly linked to early-onset non-insulin-dependent diabetes mellitus in approximately 80% of French families with this form of diabetes. We previously identified a nonsense mutation in exon 7 in one of these families and showed that it was the likely cause of glucose intolerance in this dominantly inherited disorder. Here we report the isolation and partial sequence of the human glucokinase gene and the identification of two missense mutations in exon 7, Thr-228----Met and Gly-261----Arg, that cosegregate with early-onset non-insulin-dependent diabetes mellitus. To assess the molecular mechanism by which mutations at these two sites may affect glucokinase activity, the crystal structure of the related yeast hexokinase B was used as a simple model for human beta-cell glucokinase. Computer-assisted modeling suggests that mutation of Thr-228 affects affinity for ATP and mutation of Gly-261 may alter glucose binding. The identification of mutations in glucokinase, a protein that plays an important role in hepatic and beta-cell glucose metabolism, indicates that early-onset non-insulin-dependent diabetes mellitus may be primarily a disorder of carbohydrate metabolism.

Adult↗
PubMed1992

Close linkage of glucokinase locus on chromosome 7p to early-onset non-insulin-dependent diabetes mellitus.

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem, affecting 5% of the world population. Genetic factors are important in NIDDM, but the mechanisms leading to glucose intolerance are unknown. Genetic linkage has been investigated in multigeneration families to localize, and ultimately identify, the gene(s) predisposing to NIDDM. Here we report linkage between the glucokinase locus on chromosome 7p and diabetes in 16 French families with maturity-onset diabetes of the young, a form of NIDDM characterized by monogenic autosomal dominant transmission and early age of onset. Statistical evidence of genetic heterogeneity was significant, with an estimated 45-95% of the 16 families showing linkage to glucokinase. Because glucokinase is a key enzyme of blood glucose homeostasis, these results are evidence that a gene involved in glucose metabolism could be implicated in the pathogenesis of NIDDM.

Adenosine Deaminase↗
PubMed1991

Insulin-IGF2 region on chromosome 11p encodes a gene implicated in HLA-DR4-dependent diabetes susceptibility.

A class of alleles at the VNTR (variable number of tandem repeat) locus in the 5' region of the insulin gene (INS) on chromosome 11p is associated with increased risk of insulin-dependent diabetes mellitus (IDDM), but family studies have failed to demonstrate linkage. INS is thought to contribute to IDDM susceptibility but this view has been difficult to reconcile with the lack of linkage evidence. We thus investigated polymorphisms of INS and neighbouring loci in random diabetics, IDDM multiplex families and controls. HLA-DR4-positive diabetics showed an increased risk associated with common variants at polymorphic sites in a 19-kilobase segment spanned by the 5' INS VNTR and the third intron of the gene for insulin-like growth factor II (IGF2). As INS is the major candidate gene from this region, diabetic and control sequence were compared to identify all INS polymorphisms that could contribute to disease susceptibility. In multiplex families the IDDM-associated alleles were transmitted preferentially to HLA-DR4-positive diabetic offspring from heterozygous parents. The effect was strongest in paternal meioses, suggesting a possible role for maternal imprinting. Our results strongly support the existence of a gene or genes affecting HLA-DR4 IDDM susceptibility which is located in a 19-kilobase region of INS-IGF2. Our results also suggest new ways to map susceptibility loci in other common diseases.

Base Sequence↗
PubMed1989

Determination of peritoneal glucose kinetics in rats: implications for the peritoneal implantation of closed-loop insulin delivery systems.

Peritoneal glucose kinetics were evaluated in the anaesthetized rat, to assess whether the peritoneal cavity would be a suitable site for the implantation of membrane-protected islets of Langerhans (bioartificial pancreas) or the glucose sensor of an artificial B cell. Glucose was measured in peritoneal fluid samples aspirated by needle puncture. Basal peritoneal and blood glucose concentrations were identical in 16 h fasted (n = 4) and non fasted (n = 3) animals. After 10 min of an i.v. glucose infusion (n = 15) the increment in peritoneal glucose concentration was 63 +/- 3% of the increment in blood glucose concentration and both values were significantly correlated (r = 0.92; p less than 0.001). After 10 min of glucose clamping (12.6 +/- 0.8 mmol/l), the increment in peritoneal glucose concentration was 69 +/- 3% (n = 5; p less than 0.05) of the increment in blood glucose concentration. In three additional experiments it was 93 +/- 3% of the increment in blood glucose concentration (NS), after 30 min of glucose clamping (8.0 +/- 0.5 mmol/l). Peritoneal glucose concentration monitored by a glucose sensor: (a) followed blood glucose sluggishly during a glucose clamp (n = 5), confirming the data shown above, (b) followed blood glucose with a 5 min delay and reached the same plateau after the intravenous injection of 1U insulin (n = 3; NS). We conclude that peritoneal glucose reflects blood glucose at basal state and during variations of glycaemia, nevertheless, presenting heterogeneous kinetics. These kinetics might be appropriate for a bioartificial pancreas but not for an in vivo calibration procedure, of a peritoneally implanted glucose sensor.

Animals↗
PubMed1989

Study and development of multilayer needle-type enzyme-based glucose microsensors.

Glucose oxidase (GOD) was covalently coupled to a cellulose acetate (CA) layer, using bovine serum albumin (BSA) and parabenzoquinone (PBQ) linkages. Prior to GOD coupling this CA layer was deposited on the platinum tip of a needle-type sensor and covered with an outer layer of polyurethane (PU). Such microsensors were found to be active, their GOD load reaching 1.6 to 3.0 micrograms mm-2 and their glucose response reaching 1 to 3 microA M-1 mm-2, even when the upper limit of their linear range reached 10-30 mM. Due to the multilayer structure and composition of these microsensors, small anions such as ascorbate were partially discriminated from neutral molecules such as hydrogen peroxide. When implanted subcutaneously in anaesthetized rats, sensor responses correlated correctly with blood glucose concentration but presented sensitivity coefficients significantly different to those determined in vitro: a 2 point calibration procedure was found necessary for in vivo experiments.

Animals↗
PubMed1989

Amino acid exchange between plasma and erythrocytes in vivo in humans.

To study amino acid exchange between plasma and erythrocytes in vivo, 4-h primed, continuous intravenous infusions of L-[1-13C]leucine, [15N]glycine, and L-[15N]alanine were administered to five healthy young men in the postabsorptive state. Stable isotope enrichments and amino acid levels were determined by gas chromatography-mass spectrometry in both plasma and whole blood and estimated (using hematocrit) in erythrocytes. A high concentration gradient across the erythrocyte membrane was consistently found for glycine (552 +/- 268 microM in erythrocytes vs. 155 +/- 35 microM in plasma), but not for leucine or alanine. A steady-state isotopic enrichment was observed in whole blood as well as plasma for each amino acid in every subject. Steady-state [13C]leucine enrichment in erythrocytes did not differ from plasma enrichment at steady state, the ratio of erythrocyte to plasma enrichment being 1.03 +/- 0.20 (95% confidence limits = 0.78-1.28); in contrast, this ratio reached only 0.23 +/- 0.04 and 0.59 +/- 0.09 (confidence limits 0.18-0.28 and 0.48-0.70) for [15N]glycine and [15N]alanine at steady state, respectively. These results suggest that most of erythrocyte leucine is exchangeable with plasma, whereas only a fraction of erythrocyte glycine and alanine is involved in exchange with plasma in vivo.

Adult↗