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S O'Rahilly

Publications and source records attributed to S O'Rahilly.

At least 145 records · Page 8Linked to original sources
PubMed1993

Insulin-mediated pseudoacromegaly: clinical and biochemical characterization of a syndrome of selective insulin resistance.

We have performed clinical, physiological, in vitro biochemical and genetic studies of a patient with severe insulin resistance associated with the phenotype of "pseudoacromegaly," defined as the presence of acromegaloid features in the absence of elevated levels of GH or insulin-like growth factor-I (IGF-I). Despite marked hyperinsulinemia, insulin and IGF-I binding to circulating blood cells and cultured skin fibroblasts was normal. Insulin and IGF-I-stimulated autophosphorylation of their respective receptors in cultured skin fibroblasts was also normal. However, neither insulin nor IGF-I were able to stimulate 2-deoxy D-glucose uptake by cultured skin fibroblasts. In contrast, the ability of insulin and IGF-I (or IGF-II) to stimulate amino acid uptake and thymidine incorporation into DNA was not impaired. This unique discordant signaling defect through both insulin and IGF-I receptors appeared not to be the consequence of altered expression or primary structure of the insulin receptor or the GLUT-4 glucose transporter, as assessed by several genetic and biochemical techniques. GLUT-4 expression in muscle was normal on Western blots, and SSCP screening of all 11 exons of the gene for nucleotide variation revealed no variations from normal. DNA sequencing and SSCP screening of exons 2-22 of the insulin receptor gene revealed only one variation predicted to alter the amino acid sequence (Val985-->Met). No functional differences between Met985 and wild-type human insulin receptors were evident in studies performed with Chinese hamster ovary cell transfectants that overexpress either receptor. This data combined with our previously published epidemiological data concerning the frequency of the Met985 allele, indicate that this variant insulin receptor is not responsible for the insulin resistant glucose uptake or the clinical syndrome of pseudoacromegaly. We conclude that: 1) The molecular lesion responsible for the selective biochemical defect in this individual appears to involve a signaling intermediate required for insulin and IGF-I regulation of glucose transport, and/or an effector mechanism operative in this process. 2) Cells derived from this patient may be a valuable tool in the search for such molecular mechanisms. 3) The Met985 allele is a relatively common variant which has no demonstrable adverse consequences for insulin receptor function. 4) Pseudoacromegaly can be viewed as the expected result of hyperinsulinemia driving the unopposed mitogenic and anabolic actions of insulin.

Acromegaly↗
PubMed1993

Availability of type II diabetic families for detection of diabetes susceptibility genes.

Type II diabetes is a familial disorder, as evidenced by the increased prevalence in monozygotic cotwins and first-degree relatives of affected subjects; however, its genetic etiology is largely unknown. Well-characterized pedigrees are an essential resource for the study of susceptibility genes for type II diabetes. This study describes a 5-yr search for type II diabetic families in Oxfordshire, U.K. We interviewed 950 type II diabetic subjects concerning the availability of first-degree relatives; 127 Caucasian families ascertained through a proband with type II diabetes were studied, and 589 first-degree relatives were characterized. Three large pedigrees with maturity-onset diabetes of the young, and 8 multiplex multigenerational type II diabetic pedigrees were identified. We identified 12 sib-pairs in which both siblings had type II diabetes; however, only 7 sib-pairs had both parents alive, and 2 of these had both parents affected. If one also considers one sib having diabetes and one sib having glucose intolerance as being an affected sib-pair, we identified 30 sib-pairs of which 7 had both parents affected and probably had bilineal inheritance. We identified 76 complete nuclear families with both parents and offspring available for study, but only 6 were of optimal structure for linkage analysis. In conclusion, multiplex pedigrees and type II diabetic sib-pairs with living parents are uncommon, and their ascertainment requires a substantial investment of resources. Large-scale collaborative multicenter initiatives would be needed to collect a large resource of family material for the study of susceptibility genes for type II diabetes.

Adult↗
PubMed1992

Linkage of type 2 diabetes to the glucokinase gene.

Maturity-onset diabetes of the young (MODY) is a subtype of type 2 diabetes that presents from the second decade and has an autosomal dominant mode of inheritance. We have investigated the glucokinase gene, a candidate gene for diabetes, in two MODY pedigrees. In a large 5-generation pedigree (BX) with 15 diabetic members, use of a microsatellite polymorphism revealed linkage of diabetes to the glucokinase locus on chromosome 7p. A peak lod score of 4.60 was obtained at a recombination fraction (theta) of zero. This finding suggests that a defective glucokinase gene contributes to the diabetes phenotype in this pedigree. This is not universal in MODY since linkage to the glucokinase locus was excluded in a second pedigree M (lod score = -7.36 at theta = 0). The affected members in pedigree BX were diagnosed either when young (in pregnancy or on screening) or when they presented symptomatically in middle and old age; most of them were treated by diet alone. Defects in the glucokinase gene may play an important part in the pathogenesis of type 2 diabetes.

Adolescent↗
PubMed1992

Multipoint linkage analysis of the short arm of chromosome 11 in non-insulin dependent diabetes including maturity onset diabetes of youth.

Members of three families with maturity onset diabetes of youth (MODY) and seven with "common" type 2 diabetes were typed for six DNA markers (H-RAS, INS, HBBC, PTH, CALC1, CAT) on the short arm of chromosome 11. Using conventional pairwise linkage analysis, close linkage in the MODY families was excluded for all six markers. By multipoint analysis and a genetic map of the short arm of chromosome 11, MODY was excluded from a region of at least 35 and up to 60 centiMorgans (cM) on the short arm of chromosome 11. Multipoint analysis in the type 2 families also excludes linkage to the INS, H-RAS region of at least 3 and up to 30 cM. This study using multipoint linkage analysis in non-insulin dependent diabetes provides strong evidence against a role for mutations in or around the insulin gene in the causation of MODY or type 2 diabetes in the families studied.

Chromosomes, Human, Pair 11↗
PubMed1992

Insulin receptor and insulin-responsive glucose transporter (GLUT 4) mutations and polymorphisms in a Welsh type 2 (non-insulin-dependent) diabetic population.

We have recently examined the exons encoding the insulin receptor tyrosine kinase domain and GLUT 4 in 30 subjects with Type 2 (non-insulin-dependent) diabetes mellitus using a molecular scanning approach. The variant sequences Val-Met985 and Lys-Glu1068 of the insulin receptor and Val-Ile383 of GLUT 4 were each separately found in three different diabetic subjects. In a study of a Welsh population, the GLUT 4(383) variant was found in three of 160 diabetic and none of the 80 control subjects. In this study, the same group of Welsh Type 2 diabetic and control subjects was analysed using allele-specific oligonucleotide hybridisation, single nucleotide primer extension and allele-specific restriction digestion to ascertain the frequency of the two insulin receptor mutations. The Val-Met985 mutation was found in none of the 160 Welsh Caucasian Type 2 diabetic subjects and two of 80 control subjects. The Lys-Glu1068 mutation removes a Sty 1 site and digestion of amplified exon 18 with Sty 1 confirmed the presence of the mutation in the heterozygous state in the original subject. None of the Welsh diabetic or control subjects had the Glu1068 mutation. The discovery of a very common silent polymorphism at codon 130 of GLUT 4 allowed examination of the association of this locus with Type 2 diabetes using allele-specific oligonucleotide hybridisation in a subset of the Welsh subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1992

Rapid and simultaneous detection of multiple mutations by pooled and multiplex single nucleotide primer extension: application to the study of insulin-responsive glucose transporter and insulin receptor mutations in non-insulin-dependent diabetes.

The application of molecular scanning techniques to the detection of potentially pathogenic mutations in candidate genes in patients with non-insulin-dependent diabetes has revealed a number of molecular variants of uncertain pathophysiologic significance. The determination of the significance of such variants requires large-scale population studies of the prevalence of the mutant in affected and control groups. Herein, we describe two adaptations of the technique of single nucleotide primer extension (SNuPE) which allow the simultaneous examination of large numbers of alleles at multiple loci. The usefulness of these adaptations is illustrated by their application to the simultaneous detection of three point mutations, two in the tyrosine kinase domain of the insulin receptor and one in the insulin-responsive glucose transporter (GLUT4) in a highly insulin-resistant NIDDM population. By pooling genomic or amplified DNA and performing the SNuPE reactions with three primers of different length we could readily examine 300 alleles on a single 20 lane gel. Using pooled SNuPE, we also examined a large British Caucasian control population for the prevalence of GLUT4 Ile383, a variant which has previously been reported only in NIDDM. GLUT4 Ile383 was detected in 2/42 of the highly insulin-resistant NIDDM subjects and 4/240 middle-aged blood donors. Family studies and examination of the expressed mutant transporter will be necessary to establish whether this mutation is of functional significance. Pooled and multiplex SNuPE are powerful techniques with wide applicability to population genetic studies of specific mutations.

Alleles↗
PubMed1991

Non-linkage of the islet amyloid polypeptide gene with type 2 (non-insulin-dependent) diabetes mellitus.

Type 2 (non-insulin-dependent) diabetes is associated with the deposition of islet amyloid. The major formative peptide, islet amyloid polypeptide, has recently been characterised and an abnormality of the structure or expression of this gene is a possible candidate for the inherited component of Type 2 diabetes. A restriction fragment length polymorphism of the gene has been identified with Pvu II. To study the relationship between the islet amyloid polypeptide gene and Type 2 diabetes, two distinct genetic approaches have been undertaken. Firstly, non-linkage has been demonstrated in four pedigrees, with four normoglycaemic first degree relatives having an allele associated with diabetes in other family members, and one affected relative not having the putatively associated allele. The LOD score taking age-related penetrance into account was -1.68, making linkage unlikely (p = 0.02). Secondly, in a population-based restriction fragment length polymorphism survey, no linkage disequilibrium of the alleles was found between a population of unrelated Caucasian subjects with Type 2 diabetes and a normal population. A mutation in or near the islet amyloid polypeptide gene is thus unlikely to be a common cause of Type 2 diabetes.

Amyloid↗
PubMed1991

Molecular scanning of insulin-responsive glucose transporter (GLUT4) gene in NIDDM subjects.

We investigated the prevalence of mutations in the gene encoding the major insulin-responsive facilitative glucose transporter (GLUT4) in patients with non-insulin-dependent diabetes mellitus (NIDDM). All 11 exons of the GLUT4 gene from 30 British white subjects with NIDDM were amplified using the polymerase chain reaction and screened for nucleotide sequence variation using the single-stranded conformation polymorphism (SSCP) method. No variation between the study subjects was detected in exons 1-3, 4b-8, and 10. Variant SSCP patterns were detected in exons 4a and 9. SSCP variation in exon 4a was revealed by direct nucleotide sequencing to be due to a common silent polymorphism (AAC----AAT at Asn130). One NIDDM patient demonstrated a variant SSCP pattern in exon 9. This was caused by a point mutation (GTC----ATC) at codon 383, which leads to the conservative substitution of isoleucine for valine in the putative fifth extracellular loop of the transporter. Allele-specific oligonucleotide hybridization was used to examine the frequency of this mutation in 240 Welsh white subjects (160 with NIDDM and 80 controls). The Val----Ile383 mutation was found in the heterozygous state in two diabetic subjects and no control subjects. We conclude that mutations of the GLUT4 coding sequence are very uncommon in this population of subjects with typical NIDDM. Determining whether the Ile383 GLUT4 variant present in 3 diabetic subjects contributes in any way to their disease will require further study.

Alleles↗
PubMed1991

Detection of mutations in insulin-receptor gene in NIDDM patients by analysis of single-stranded conformation polymorphisms.

We used the recently described technique of single-stranded conformation-polymorphism (SSCP) analysis to examine the insulin-receptor locus. First, the ability of the method to detect known mutations and polymorphisms in the insulin-receptor coding sequence was assessed. Regions of the insulin-receptor sequence containing 16 different nucleotide changes, 9 in patient genomic DNA and 7 as cloned cDNA in plasmids, were analyzed. All 9 patient genomic DNA mutants and 5 of 7 plasmid mutants exhibited variant SSCP patterns. To investigate the potential of the technique for screening many patients, the 5 exons that encode the tyrosine kinase domain of the insulin receptor were examined in 30 unrelated white subjects with non-insulin-dependent diabetes mellitus (NIDDM). Exons 17-21 were amplified from genomic DNA with polymerase chain reaction and subjected to SSCP analysis. Exons 19, 20, and 21 revealed no bands of aberrant migration, suggesting a high degree of conservation of these sequences. One diabetic subject had an SSCP variant in exon 18. Direct sequencing of this subject's genomic DNA revealed a heterozygous missense mutation (Lys1068----Glu1068). Five different SSCP patterns were detected in exon 17. Based on direct sequencing, these patterns were explained by combinations of three different nucleotide substitutions, two of which were common silent polymorphisms. One subject had a heterozygous missense mutation Val985---- Met985. Allele-specific oligonucleotide hybridization confirmed the presence of these mutations in the appropriate diabetic subjects and also detected the Val985 mutation in heterozygous form in 1 of 13 nondiabetic white subjects. SSCP analysis is a sensitive rapid method for screening for mutations in the insulin-receptor gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1990

Chromosome 11 allele loss in sporadic insulinoma.

DNA was extracted from tissue samples of three unrelated cases of insulinoma. Chromosome 11 allele loss was investigated using several chromosome 11 specific probes which detect restriction fragment length polymorphisms. In one case, which proved informative for many of the chromosome 11 markers, allele loss was shown on both 11p and 11q. This finding is of considerable interest as the allele loss closely corresponds to that recently reported in insulinomas occurring in the familial multiple endocrine neoplasia type 1 (MEN-1) syndrome.

Adenoma, Islet Cell↗
PubMed1990

Plasma proinsulin in first-degree relatives of type 2 diabetic subjects.

Glucose intolerant relatives of Type 2 diabetic subjects have impaired insulin secretory responses to glucose but their proinsulin secretion has not been assessed. Plasma intact proinsulin was measured in 101 normoglycaemic and glucose intolerant first-degree relatives of Type 2 diabetic subjects both fasting and one hour after an infusion of glucose of 5 mg glucose.kg ideal weight.min-1. Geometric mean (+/- SD) plasma proinsulin increased from 2.4 (+2.5-1.2) and increased to 4.5 (+4.2-2.1) pmol/l at 1 hour (p less than 0.001). Linear regression revealed no relationship of fasting or achieved proinsulin with sex or obesity and a non-significant trend towards increasing fasting and achieved proinsulin with age and fasting plasma glucose. Proinsulin was assessed as a ratio to the simultaneous plasma C-peptide to estimate the relative amounts of insulin and proinsulin secreted by the beta-cells. Analysis of partial correlation coefficients, controlling for age and obesity, showed that the Achieved Proinsulin/Achieved C-peptide ratio was related to both fasting (r = 0.27, p = 0.004) and achieved plasma glucose (r = 0.25, p = 0.008). Glucose intolerant relatives (n = 37) had a small but significant increase in relative proinsulin secretion compared with normoglycaemic relatives (n = 64) (Achieved Proinsulin/Achieved C-peptide 0.07 +/- 0.05 vs 0.04 +/- 0.02 p less than 0.01). This is in accord with abnormal beta cell function being an early feature of Type 2 diabetes but does not distinguish between a primary beta-cell abnormality and a secondary effect of mild hyperglycaemia.

Adult↗
PubMed1989

Analysis of the HepG2/erythrocyte glucose transporter locus in a family with type 2 (non-insulin-dependent) diabetes and obesity.

A recent report has shown an association between a specific Xba1 restriction fragment of the human HepG2-Erythrocyte glucose transporter gene and Type 2 (non-insulin dependent) diabetes. To further examine the significance of this finding we have studied Type 2 diabetic pedigrees for linkage between the Xba1 alleles of this glucose transporter gene and diabetes. One large pedigree, in which the diabetic phenotype was associated with obesity and insulin resistance, was informative. In this family the disease did not co-segregate with the glucose transporter locus. Formal linkage analysis was performed assuming autosomal dominant inheritance with age-dependent penetrance. At putative gene frequencies of 0.01 and 0.001 the logarithm of the odds for linkage versus non-linkage at a recombination fraction of 0.001 was -1.84 and -3.32 respectively (a value of less than -2 indicates definite non-linkage). Genetic variations in the HepG2-Erythrocyte glucose transporter gene are unlikely to be responsible for the development of diabetes in this pedigree.

Adult↗
PubMed1989

Analysis of the pro-opiomelanocortin gene in non-insulin dependent diabetic families.

Products of the pro-opiomelanocortin gene have been shown to have marked effects on insulin secretion. Selective antagonists of beta-endorphin have been reported to correct the impaired insulin secretory response to glucose seen in non-insulin dependent diabetes. Families with an autosomal dominant pattern of inheritance of diabetes were studied for possible linkage between diabetes and the pro-opiomelanocortin locus by examining the inheritance of a Rsa 1 restriction fragment length polymorphism. In two families with classical Type 2 diabetes there were recombinants between the disease and the pro-opiomelanocortin locus. In a family with maturity-onset diabetes of the young there were only two informative meoises, but there was a crossover between the disease and the pro-opiomelanocortin gene locus. Inherited defects in or near the pro-opiomelanocortin gene locus are unlikely to be directly involved in the aetiology of non-insulin dependent diabetes.

Alleles↗
PubMed1988

Impaired pulsatile secretion of insulin in relatives of patients with non-insulin-dependent diabetes.

In fasting nondiabetic subjects, insulin is secreted in regular pulses every 12 to 15 minutes, but patients with non-insulin-dependent diabetes lack regular oscillatory insulin secretion. To investigate whether abnormal insulin oscillations are an early feature of diabetes, we studied 10 minimally glucose-intolerant first-degree relatives of patients with non-insulin-dependent diabetes and 10 controls matched for age and obesity. We performed a time-series analysis of fasting plasma insulin levels in blood samples obtained at 1-minute intervals for 150 minutes. Fasting plasma glucose levels were higher in the relatives than in the controls (mean +/- SD, 5.4 +/- 0.7 vs. 4.4 +/- 0.3 mmol per liter). Autocorrelation of pooled data showed no regular oscillatory activity in the relatives but a 13-minute cycle in the controls (r = 0.23, P less than 0.001). Similarly, Fourier transform analysis showed no significant peak in the relatives but the expected significant peak at 13 to 14 minutes in the controls (P less than 0.05). First-phase (0 to 10 minutes) insulin secretory responses to glucose administered intravenously were not significantly impaired in the relatives (geometric mean, 188 pmol per liter [26.2 mU per liter]; range of SD, +103 to -67 pmol per liter [+14.4 to -9.3 mU per liter]), as compared with the controls (geometric mean, 231 pmol per liter [32.2 mU per liter]; range of SD, +131 to -83 pmol per liter [+18.2 to -11.6 mU per liter]). We conclude that abnormal oscillatory insulin secretion may be an early phenomenon in the development of non-insulin-dependent diabetes.

Adult↗
PubMed1988

Type 2 (non-insulin-dependent) diabetes mellitus. New genetics for old nightmares.

In the last five years, genetic markers for a large number of diseases have been localised using linkage analysis of DNA polymorphisms in affected families. The site of the genetic defect or defects leading to Type 2 (non-insulin-dependent) diabetes mellitus, a common illness with a major genetic component, remains unknown. This is due, at least in part, to the lack of large well-defined Type 2 diabetic pedigrees suitable for linkage analysis. There are several features of the disease which make large pedigrees difficult to find. The late age of onset of most probands means that informative older generations are often dead, while there is difficulty in detecting disease in younger generations. The diagnostic criteria for diabetes are, as yet, dependent on an arbitrary cut-off along a continuum of plasma glucose. The high prevalence of the disease may also produce problems as, in any given family, diabetogenic genes may be contributed by more than one parent. Varieties of the disease with a well-defined inheritance, such as maturity onset diabetes of youth, are more suitable for linkage analysis but might be due to defects at a different gene locus. Despite these difficulties, once large well-defined pedigrees have been found, linkage analysis using both candidate genes and random highly polymorphic markers is the strategy most likely to find genetic markers for the disease.

Diabetes Mellitus, Type 2↗