Detection of human apolipoprotein E3, E2, and E4 genotypes by an allele-specific oligonucleotide-primed polymerase chain reaction assay: development and validation

A polymerase chain reaction (PCR) assay has been developed and validated by using allele-specific oligonucleotide (ASO) primers to specifically amplify E3, E2, and E4 polymorphic sequences of the human apolipoprotein E (apo E) genes. Degenerate ASOs containing one or two additional 3' mismatches provided greater specificity than did ASOs containing a single mid-sequence or 3' allele-specific mismatch with plasmid pEB4 or genomic DNA as template. Optimal specificity and efficiency of amplification did not correlate with primer annealing conditions, whether determined theoretically or via oligo-melting experiments. Pre-cycling denaturation times and high cycling denaturation temperatures were also required for optimal amplification, presumably because of the high G:C content (75-85%) of apo E gene sequences. Conditions permissive for amplification and discrimination with plasmid DNA did not transpose favorably to amplification from human genomic DNA from peripheral blood leukocytes; the latter required nested primer reactions. These data may be valuable in predicting PCR assay conditions for other G:C-rich sequences containing polymorphic sequence differences. The assay described is both more accurate and rapid (24 h) than previously described methods for phenotyping or genotyping human apo E from blood specimens.

Detection of human apolipoprotein E3, E2, and E4 genotypes by an allele-specific oligonucleotide-primed polymerase chain reaction assay: development and validation

A polymerase chain reaction (PCR) assay has been developed and validated by using allele-specific oligonucleotide (ASO) primers to specifically amplify E3, E2, and E4 polymorphic sequences of the human apolipoprotein E (apo E) genes. Degenerate ASOs containing one or two additional 3' mismatches provided greater specificity than did ASOs containing a single mid-sequence or 3' allele-specific mismatch with plasmid pEB4 or genomic DNA as template. Optimal specificity and efficiency of amplification did not correlate with primer annealing conditions, whether determined theoretically or via oligo-melting experiments. Pre-cycling denaturation times and high cycling denaturation temperatures were also required for optimal amplification, presumably because of the high G:C content (75-85%) of apo E gene sequences. Conditions permissive for amplification and discrimination with plasmid DNA did not transpose favorably to amplification from human genomic DNA from peripheral blood leukocytes; the latter required nested primer reactions. These data may be valuable in predicting PCR assay conditions for other G:C-rich sequences containing polymorphic sequence differences. The assay described is both more accurate and rapid (24 h) than previously described methods for phenotyping or genotyping human apo E from blood specimens.

DRB genotyping supports recessive inheritance of DR3-associated susceptibility to insulin-dependent diabetes mellitus

The mode of inheritance of HLA-associated susceptibility to insulin-dependent diabetes mellitus was investigated by the antigen genotype frequency among patients method in a white Caucasian population and a North Indian Asian population. DR genotypes were determined by DRB/DQB RFLP analysis. In white Caucasians, simple recessive and simple additive inheritance of a single HLA-associated disease susceptibility allele were rejected (P less than .025 and P less than 10(-6), respectively). The data were compatible with a three-allele model of disease susceptibility. In North Indian Asians, simple additive inheritance was rejected (P less than 10(-6)). The observed genotype frequencies were compatible with a single DR3-associated disease susceptibility allele which is inherited recessively. These data show that study of DR genotypes in populations of different ethnic origins may further the understanding of inherited susceptibility to insulin-dependent diabetes mellitus.

Pathogenesis of diabetic microangiopathy: an overview

Major susceptibility factors for diabetic microangiopathy include duration of disease and probably quality of metabolic control. The mechanism of development of microangiopathy is incompletely understood but appears to involve functional abnormalities within the microcirculation, enhanced glucose metabolism, hemostatic abnormality, and genetic susceptibility. This article reviews the factors believed to be involved in pathogenesis and attempts to draw these together by suggesting a sequence of pathogenic interactions that could result in the microvascular changes seen in susceptible target organs. Possibilities for therapeutic intervention based on these pathogenic mechanisms are discussed. A small pilot trial of an oral hypoglycemic agent, gliclazide, is reported, providing evidence for a specific action of this drug on thromboxane synthesis and platelet aggregation. This is independent of glycemic control and may in part be mediated by a fall in lipid peroxides.

HLA-DQA1 and -DQB1 alleles associated with genetic susceptibility to IDDM in a black population

Transracial analysis provides a method of distinguishing primary associations between insulin-dependent diabetes mellitus (IDDM) and HLA class II alleles from those secondary to linkage disequilibrium. Blacks show DR-DQ relationships that are different from other races and are a useful group in which to investigate HLA-D region associations with IDDM. In this study, the frequencies of HLA-DQA1 and -DQB1 alleles in Afro-Caribbean IDDM and control subjects were compared. Alleles were identified with sequence-specific oligonucleotide probing. The DQA1 allele A3 was positively associated with IDDM (relative risk [RR] = 25.3, corrected P [Pc] less than 7.0 x 10(-6). The DQB1 alleles DQw2 and DQw8 were also positively associated (RR = 4.7, Pc less than 6.5 x 10(-3) and RR = 12.3, Pc = 3.4 x 10(-3), respectively). The A1.2 and DQw6 alleles were negatively associated (RR = 0.16, Pc less than 3.5 x 10(-3) and RR = 0.15, Pc = 2.4 x 10(-2), respectively). These findings were compared to data from other races. The positive associations with A3 and DQw2 are consistent with all racial groups investigated. The negative association with DQw6 is present in all racial groups in which it is a common allele. These findings suggest that DQ alleles, and hence DQ molecules, may directly affect predisposition to IDDM.

Genetics of diabetes. Trans-racial gene mapping studies

A major component of inherited susceptibility to IDDM is associated with one or more loci in the MHC. Identification of the primary susceptibility genes has been complicated by the low frequency of recombination, i.e. linkage disequilibrium, within the MHC. It is difficult to distinguish whether a detected genetic association with the disease is primary, or secondary due to linkage disequilibrium with an allele at another locus which is directly predisposing. During the evolution of different races, however, recombination within the MHC has occurred and population-specific MHC haplotypes exist. Primary susceptibility allels should be associated with disease in all racial groups, regardless of genetic background. It is unlikely that disease associations secondary to linkage disequilibrium will be consistent in these groups. This chapter reviews the known associations of candidate class II susceptibility alleles with IDDM in the five largest racial groups; white Caucasians, Asian Indians, Negroids, Japanese and Chinese. These trans-racial studies suggest that the DQ molecule has a primary role in predisposition to IDDM. There are consistent findings of a positive association with the DQA1*0301 allele and negative associations with the DQB1*0602 and DQB1*0603 alleles. These two alleles differ by a single codon and so the encoded DQ beta chains are likely to have similar functions. DR4-associated susceptibility is associated with the DQA1*0301 allele in all races tested so far but this allele cannot be the only susceptibility factor on this haplotype. The identity of the DR3-associated susceptibility factor remains unclear but the DQB1*0201 allele is a candidate. If DQB1*0201 is involved, the existence of a protective factor on the neutral DR7-DQB1*0201 haplotypes is indicated. Analysis of DR9 associated susceptibility implicates a non-DR/DQ predisposing factor.

Some recent advances in non-communicable diseases in the tropics. 2. Diabetes mellitus in the tropics

Diabetes mellitus occurs in all parts of the world, but with striking differences in prevalence and mode of presentation. This article considers the epidemiology of diabetes world-wide and specifically the pattern of diabetes in the tropics which appears to differ from that seen in Europe and the USA. Detailed epidemiological studies will help both in understanding diabetes pathogenesis and in rational management of this very important and common disease.

Transferrinuria in type 2 diabetes: the effect of glycaemic control

Urinary excretion rates of transferrin, albumin, N-acetyl-beta-D-glucosaminidase (NAG) and alpha-1-microglobulin (A1M) were measured in type 2 (non-insulin-dependent) diabetic patients at diagnosis and after 6 and 12 weeks treatment. Initially 21 (53%) patients had elevated transferrin excretion rates. The proportion of patients with raised transferrin excretion rates fell to 30% at 6 weeks and 20% at 12 weeks with treatment of diabetes. At diagnosis 11 (28%) patients had elevated albumin excretion rates and 10 of these had elevated transferrin excretion rates. After 6 weeks treatment only six (15%) had elevated albumin excretion rates and by 12 weeks this number had fallen to four (10%). NAG and A1M levels also fell with treatment of diabetes. There were correlations between the transferrin excretion rate and albumin excretion rate (r = 0.86, P less than 0.0001), transferrin excretion rate and NAG (r = 0.46, P less than 0.0001), and transferrin excretion rate and A1M (r = 0.55, P less than 0.0001) at each visit. There were weaker correlations between the albumin excretion rate and A1M and NAG at each visit. The correlations between the transferrin excretion rate and markers of tubular function (NAG and A1M) suggest that tubular dysfunction may play a part in renal loss of transferrin in diabetes mellitus. There were no differences in transferrin excretion rates between patients with and without evidence of complications.

Disturbed handling of ascorbic acid in diabetic patients with and without microangiopathy during high dose ascorbate supplementation

Abnormalities of ascorbic acid metabolism have been reported in experimentally-induced diabetes and in diabetic patients. Ascorbate is a powerful antioxidant, a cofactor in collagen biosynthesis, and affects platelet activation, prostaglandin synthesis and the polyol pathway. This suggests a possible close interrelationship between ascorbic acid metabolism and pathways known to be influenced by diabetes. We determined serum ascorbic acid and its metabolite, dehydroascorbic acid, as indices of antioxidant status, and the ratio, dehydroascorbate/ascorbate, as an index of oxidative stress, in 20 matched diabetic patients with and 20 without microangiopathy and in 22 age-matched control subjects. Each study subject then took ascorbic acid, 1 g daily orally, for six weeks with repeat measurements taken at three and six weeks. At baseline, patients with microangiopathy had lower ascorbic acid concentrations than those without microangiopathy and control subjects (42.1 +/- 19.3 vs 55.6 +/- 20.0, p less than 0.01, vs 82.9 +/- 30.9 mumol/l, p less than 0.001) and elevated dehydroascorbate/ascorbate ratios (0.87 +/- 0.46 vs 0.61 +/- 0.26, p less than 0.01, vs 0.38 +/- 0.14, p less than 0.001). At three weeks, ascorbate concentrations rose in all groups (p less than 0.0001) and was maintained in control subjects (151.5 +/- 56.3 mumol/l), but fell in both diabetic groups by six weeks (p less than 0.01). Dehydroascorbate/ascorbate ratios fell in all groups at three weeks (p less than 0.0001) but rose again in the diabetic groups by six weeks (p less than 0.001) and was unchanged in the control subjects. Dehydroascorbate concentrations rose significantly from baseline in all groups by six weeks of ascorbic acid supplementation (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal blood pressure response to exercise in normoalbuminuric insulin dependent diabetic patients

Eight male normoproteinuric Type I (insulin dependent) diabetic patients and eight age- and sex-matched non-diabetic control subjects were studied for their response to exercise. Systolic blood pressure showed an exaggerated response to exercise in the diabetic group (median 123, range 98-151 mmHg, pre-exercise vs. 187, 163-217 mmHg, immediately post exercise P less than 0.01) compared to the control group (median 112 (100-145) pre-exercise, 153 (138-178) post exercise). Resting noradrenaline levels were lower in the diabetic (D) compared with the control (C) group (D: 1.66, 0.55-3.92 nmol/l vs. C: 2.96, 2.04-4.49 nmol/l, P less than 0.02). Levels rose during exercise by 79% (25-307%) and 43% (4-90%) respectively (NS). Resting urinary sodium was raised in the diabetic group and fell during exercise (P less than 0.05) (D: 146, 74-244 mumol/min, C: 108.5 (83.4-151.0) pre-exercise vs. D: 73, 48-264 mumol/min, C: 81.7 (23.0-92.0) post exercise). Resting atrial natriuretic peptide levels were lower in the diabetic group (D: 10.1, 4.3-16.9 pmol/l vs. C: 16.0, 9.5-22.9 pmol/l, P less than 0.02) and levels rose significantly in both groups during exercise (D: 25.9, 5.2-38.9 pmol/l vs. C: 28.6, 17.3-47.2 pmol/l, P less than 0.05). We conclude that exercise provokes an exaggerated rise in systolic blood pressure and decrease in urinary sodium excretion in normoalbuminuric diabetic patients. These findings may reflect increased sensitivity to the renin-angiotensin-aldosterone system. Reduced atrial natriuretic peptide levels may stimulate sodium retention and increased blood pressure in early diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Allele-specific gene probing supports the DQ molecule as a determinant of inherited susceptibility to type 1 (insulin-dependent) diabetes mellitus

Trans-racial analysis of disease associations has improved mapping of MHC-linked susceptibility to Type 1 (insulin-dependent) diabetes mellitus. In this study the contributions of the MHC class II DQA1 and DQB1 genes were investigated. Sequence-specific oligonucleotide gene probing in Type 1 diabetic and control subjects of North Indian origin supported the DQw1.18 allele of the DQB1 gene as a determinant of inherited protection against Type 1 diabetes (RR = 0.12, pc less than 0.05). The A3 allele of the DQA1 gene was positively associated with the disease, (RR = 3.6, pc less than 0.05), as was the DQw2 allele of the DQB1 gene (RR = 4.6, pc less than 0.01). Trans-racial comparison of these disease associations indicates that DQ alleles may directly determine an element of inherited susceptibility to Type 1 diabetes.

Clinical and neurophysiological studies of aldose reductase inhibitor ponalrestat in chronic symptomatic diabetic peripheral neuropathy

Increased flux through the polyol pathway mediated by the enzyme aldose reductase may be associated with the development of diabetic neuropathy. Fifty-four diabetic patients (median age 56 yr, range 25-65 yr) with chronic neuropathic symptoms were randomly allocated to placebo or aldose reductase inhibition (300 or 600 mg ponalrestat ICI 128436) groups for 24 wk. Patients with vibration perception thresholds (VPTs) greater than 35 V at the great toe or thermal difference thresholds (TTs) greater than 10 degrees C on the dorsum of the foot were excluded from the trial. No significant changes were observed in symptoms of pain, numbness, or paresthesia between ponalrestat and placebo groups, and there were no improvements in VPT or TT at several sites. Posterior tibial nerve conduction velocity changed from 35.3 +/- 4.9 m/s at baseline to 33.4 +/- 4.0 m/s at 24 wk (NS) with placebo compared with 37.6 +/- 5.6 vs. 37.2 +/- 8.7 m/s (NS) with 300 mg ponalrestat and 34.5 +/- 6.1 vs. 36.2 +/- 6.8 m/s (NS) with 600 mg ponalrestat. Further studies are indicated with intervention at an earlier stage in the evolution of neuropathy and for longer periods.

Transfer from animal insulins to semisynthetic human insulin: a study in four centres

The effects of transfer from animal insulin to semisynthetic human insulin on glycaemic control, insulin dose and anti-insulin antibodies were investigated in a total of 108 patients at four centres in a double-blind controlled study of eight months duration. Six months after transfer from porcine to human insulin there was a mean (+/- SE) increase in pre-breakfast blood glucose of 1.1 +/- 0.6 mmol l-1 (vs a reduction of 1.6 +/- 0.7 mmol l-1 in controls) (p less than 0.01), and a mean increase of pre-lunch blood glucose of 0.9 +/- 0.7 mmol l-1 (vs a reduction of 1.14 +/- 0.7 mmol l-1 in controls) (p less than 0.05). Six months after transfer from bovine to human insulin, there were no significant changes in blood glucose. Glycated haemoglobin showed no significant change six months after transfer from either bovine or porcine to human insulin. Hypoglycaemic symptoms, the total daily insulin dose, and the ratio of short- to intermediate-acting insulin did not change significantly after transfer from either bovine or porcine to human insulin. Transfer from bovine to human insulin resulted in a significant decline in anti-human insulin antibodies (mean (range): 50.5(14.8-125)% of initial levels), vs controls (113(43.4-234)% of initial levels; p = 0.034), and a non-significant decline in anti-bovine insulin antibodies (52.2(25.8-111)% vs 81.7(42.5-128)%; p = 0.082).

Is candidiasis the true cause of vulvovaginal irritation in women with diabetes mellitus?

Vulvovaginitis is common in diabetic women and is often treated with antifungal agents on the assumption that the causative organism is Candida albicans. In a survey of 100 consecutive diabetic women attending a diabetes clinic 36 had complained to their general practitioner about vulvovaginal irritation during the past three years and 26 were treated with antifungal agents without a vaginal examination or swabs being taken. In a separate study 27 post-menopausal women with non-insulin dependent diabetes and symptoms of vulvovaginitis were investigated. The organisms cultured were: Candida albicans (n = 6), beta haemolytic streptococci (n = 14), Gardnerella vaginalis (n = 2), Staphylococcus aureus (n = 2), Streptococcus milleri (n = 1), Streptococcus faecalis (n = 1), Klebsiella oxytoca (n = 1), no organisms (n = 3). Where a bacterial organism was isolated symptoms resolved in all but one case with appropriate antibiotic treatment. It is recommended that the practice of initiating antifungal treatment without taking high vaginal swabs should be reviewed and treatment should be given specifically rather than empirically.

Identification of susceptibility loci for type 1 (insulin-dependent) diabetes by trans-racial gene mapping

A major component of inherited susceptibility to Type 1 (insulin-dependent) diabetes mellitus has been mapped to the major histocompatibility complex. Certain gene alleles in this region determine susceptibility and resistance to the disease. Mapping of susceptibility is hindered by the limitations of conventional tissue typing techniques, and by strong linkage disequilibrium within this part of the genome. Recombinant DNA technology and trans-racial studies have been used to allow finer mapping of genetic predisposition to Type 1 diabetes. These techniques have localised alleles encoding susceptibility and resistance to the DQ region. Other alleles determining disease susceptibility remain poorly localised.

A predominantly adrenaline-secreting phaeochromocytoma

A 61-year-old woman who presented with diabetes, nausea, weight loss and sweating was found to have a phaeochromocytoma secreting adrenaline, with a small amount of N-methyladrenaline. There was no significant increase in noradrenaline secretion. She was normotensive, and developed profound hypotension in response to the alpha-adrenergic antagonist phenoxybenzamine. These features are unusual in phaeochromocytoma, but similar features occurred in the very few previous reported cases of pure adrenaline-secreting phaeochromocytoma. We conclude that it is important to identify such patients, so that they should not be given alpha-adrenergic antagonist drugs.

Free radicals and antioxidant systems in health and disease

Free radical (FR) mechanisms have both beneficial and deleterious actions in vivo. Intensive scientific interest in FRs over the last 20 years has led to a clearer understanding of their roles and helped to clarify the contribution of our intrinsic defence systems (antioxidants) in limiting FR-induced tissue damage. As more and more conditions are shown to have a FR aetiology it becomes imperative to develop newer therapies to prevent and treat FR-induced disease.

Analysis of MHC class II DNA polymorphisms in Negroid subjects

Study of the MHC class II region is complicated by strong linkage disequilibrium between DR and DQ. Comparison of DR-DQ haplotypes between different races partly resolves this problem. We present the results of an analysis of DRB, DQA and DQB restriction fragment length polymorphisms in serologically DR-typed subjects of Negroid origin. Clearly distinguishable DRB RFLPs were observed for DR1,2,5,7 and w8. DR4,9 and w10 were uncommon in this group. DR3 was associated with two extended haplotypes, one characterised by the DQw4 allele, the other by the DQw2 allele. A recently recognised DQB RFLP (DQB 2c) was associated with DR7 and also occurred on DR5 and DR9 haplotypes. Both DR5 and DRw6 were heterogeneous in their DR-DQ relationships. Negroid subjects exhibit DR-DQ relationships distinct from other races. These provide scope for further study of MHC class II associations with disease.

Impact of microangiopathy on chronic symptomatic peripheral neuropathy

The role of microvascular disease in the aetiology of diabetic peripheral neuropathy remains controversial. Muscle capillary basement membrane thickening (MCBMT) and increased albumin excretion rates (AER) are features of generalized diabetic microangiopathy and may relate to the severity of neuropathy. We have studied 19 patients with neuropathy of greater than 12 months duration and assessed relationships between the severity of neuropathy and MCBMT, AER, presence of retinopathy, age and duration of diabetes. Nine patients had retinopathy and 10 did not. The two groups of patients were well matched for age, type of diabetes and HbA1% but diabetic patients with retinopathy had significantly longer duration of diabetes (median duration 22 yr, range 3-42 yr compared with patients without retinopathy (6 yr range 1-20 yr p less than 0.05). The group with retinopathy had significantly greater median MCBMT 3,077 A (range 741-10,732 A) than their age matched non-diabetic controls 2,256 A (1,290-4,406 A p less than 0.02) or the 10 diabetic patients without retinopathy 1,599 A (805-5,152 A). The patients with retinopathy also had greater median AER 88 micrograms/min (range 8-200 micrograms/min) compared with patients without retinopathy 8 micrograms/min (2-63 micrograms/min p less than 0.05), and had significantly more severe neuropathic features on a 12 point neurophysiological ranking scale (p less than 0.05). This study showed an association between retinopathy and severity of neuropathy but there were no associations between severity of neuropathy or AER with MCBMT. Severe chronic peripheral neuropathy is associated with microangiopathic complications.