Polymorphism in the 5' flanking region of the human insulin gene: a genetic marker for non-insulin-dependent diabetes

Structural insights into i-motif DNA structures in sequences from the insulin-linked polymorphic region

The insulin-linked polymorphic region is a variable number of tandem repeats region of DNA in the promoter of the insulin gene that regulates transcription of insulin. This region is known to form the alternative DNA structures, i-motifs and G-quadruplexes. Individuals have different sequence variants of tandem repeats and although previous work investigated the effects of some variants on G-quadruplex formation, there is not a clear picture of the relationship between the sequence diversity, the DNA structures formed, and the functional effects on insulin gene expression. Here we show that different sequence variants of the insulin linked polymorphic region form different DNA structures in vitro. Additionally, reporter genes in cellulo indicate that insulin expression may change depending on which DNA structures form. We report the crystal structure and dynamics of an intramolecular i-motif, which reveal sequences within the loop regions forming additional stabilising interactions that are critical to formation of stable i-motif structures. The outcomes of this work reveal the detail in formation of stable i-motif DNA structures, with potential for rational based drug design for compounds to target i-motif DNA.

Prediction and prevention of type 1 diabetes: update on success of prediction and struggles at prevention

Type 1 diabetes mellitus (T1DM) is the archetypal example of a T cell-mediated autoimmune disease characterized by selective destruction of pancreatic β cells. The pathogenic equation for T1DM presents a complex interrelation of genetic and environmental factors, most of which have yet to be identified. On the basis of observed familial aggregation of T1DM, it is certain that there is a decided heritable genetic susceptibility for developing T1DM. The well-known association of T1DM with certain human histocompatibility leukocyte antigen (HLA) alleles of the major histocompatibility complex (MHC) was a major step toward understanding the role of inheritance in T1DM. Type 1 diabetes is a polygenic disease with a small number of genes having large effects (e.g., HLA) and a large number of genes having small effects. Risk of T1DM progression is conferred by specific HLA DR/DQ alleles [e.g., DRB1*03-DQB1*0201 (DR3/DQ2) or DRB1*04-DQB1*0302 (DR4/DQ8)]. In addition, the HLA allele DQB1*0602 is associated with dominant protection from T1DM in multiple populations. A concordance rate lower than 100% between monozygotic twins indicates a potential involvement of environmental factors on disease development. The detection of at least two islet autoantibodies in the blood is virtually pre-diagnostic for T1DM. The majority of children who carry these biomarkers, regardless of whether they have an a priori family history of the disease, will develop insulin-requiring diabetes. Facilitating pre-diagnosis is the timing of seroconversion which is most pronounced in the first 2 yr of life. Unfortunately the significant progress in improving prediction of T1DM has not yet been paralleled by safe and efficacious intervention strategies aimed at preventing the disease. Herein we summarize the chequered history of prediction and prevention of T1DM, describing successes and failures alike, and thereafter examine future trends in the exciting, partially explored field of T1DM prevention.

Exercise training, genetics and type 2 diabetes-related phenotypes

Type 2 diabetes mellitus (T2DM) is at virtually pandemic levels world-wide. Diabetes has been referred to as 'a geneticist's nightmare'. However, dramatic advances in our understanding of the genetics of T2DM have occurred in the past 5 years. While endurance exercise training and increased habitual physical activity levels have consistently been shown to improve or be associated with improved T2DM-related phenotypes, there is substantial interindividual variation in these responses. There is some evidence that T2DM-related phenotype responses to exercise training are heritable, indicating that they might have a genetic basis. Genome-wide linkage studies have not identified specific chromosomal loci that could account for these differences, and no genome-wide association studies have been performed relative to T2DM-related phenotype responses to exercise training. From candidate gene studies, there are relatively strong and replicated data supporting a role for the PPARγ Pro12Ala variant in the interindividual differences in T2DM-related phenotype responses to training. This is a potentially important candidate locus because it affects T2DM susceptibility, has high biological plausibility and is the target for the primary pharmaceutical method for treating T2DM. Is it time to conduct a hypothesis-driven large-scale exercise training intervention trial based on PPARγ Pro12Ala genotype with T2DM-related phenotypes as the primary outcome measures, while also assessing potential mechanistic changes in skeletal muscle and adipose tissue? Or would it be more appropriate to propose a smaller trial to address the specific skeletal muscle and adipose tissue mechanisms affected by the interaction between the PPARγ Pro12Ala genotype and exercise training?

Do genetic variations alter the effects of exercise training on cardiovascular disease and can we identify the candidate variants now or in the future?

Cardiovascular disease (CVD) and CVD risk factors are highly heritable, and numerous lines of evidence indicate they have a strong genetic basis. While there is nothing known about the interactive effects of genetics and exercise training on CVD itself, there is at least some literature addressing their interactive effect on CVD risk factors. There is some evidence indicating that CVD risk factor responses to exercise training are also heritable and, thus, may have a genetic basis. While roughly 100 studies have reported significant effects of genetic variants on CVD risk factor responses to exercise training, no definitive conclusions can be generated at the present time, because of the lack of consistent and replicated results and the small sample sizes evident in most studies. There is some evidence supporting “possible” candidate genes that may affect these responses to exercise training: APO E and CETP for plasma lipoprotein-lipid profiles; eNOS, ACE, EDN1, and GNB3 for blood pressure; PPARG for type 2 diabetes phenotypes; and FTO and BAR genes for obesity-related phenotypes. However, while genotyping technologies and statistical methods are advancing rapidly, the primary limitation in this field is the need to generate what in terms of exercise intervention studies would be almost incomprehensible sample sizes. Most recent diabetes, obesity, and blood pressure genetic studies have utilized populations of 10,000–250,000 subjects, which result in the necessary statistical power to detect the magnitude of effects that would probably be expected for the impact of an individual gene on CVD risk factor responses to exercise training. Thus at this time it is difficult to see how this field will advance in the future to the point where robust, consistent, and replicated data are available to address these issues. However, the results of recent large-scale genomewide association studies for baseline CVD risk factors may drive future hypothesis-driven exercise training intervention studies in smaller populations addressing the impact of specific genetic variants on well-defined physiological phenotypes.

Polymorphisms in candidate genes for type 2 diabetes mellitus in a Mexican population with metabolic syndrome findings

The metabolic or insulin resistance syndrome, characterized by hypertension, dyslipidemia, glucose intolerance and hyperinsulinemia, may have genetic determinants. The insulin gene (INS), insulin receptor gene (INSR) and insulin receptor substrate 1 gene (IRS1) have been proposed as candidate genes. We examined eight polymorphisms in these genes in 163 individuals from Yucatan, Mexico; this population has a high prevalence of obesity, type 2 diabetes mellitus and dyslipidemia. Subjects were evaluated for body mass index (BMI) and blood pressure. Blood samples were collected to determine glucose, insulin, triglycerides and cholesterol levels, as well as for DNA isolation. Restriction fragment length polymorphisms in INS, INSR and IRS1 were identified by polymerase chain reaction and digestion with selected restriction enzymes. Among the eight polymorphisms analyzed, the PstI polymorphism in INS was significantly associated with hypertriglyceridemia and with the presence of at least one abnormality related to the metabolic syndrome (P=0.007 and 0.004, respectively). The MaeIII polymorphism in INS was associated with fasting hyperinsulinemia (P=0.045). In multilocus analyses including both INS polymorphisms, significant associations were seen with hypertriglyceridemia (P=0.006), hypercholesterolemia (P=0.031) and with presence of at least one metabolic abnormality (P=0.009). None of the polymorphisms in INSR or IRS1 was associated with any of these traits. These findings suggest that the insulin gene may be an important determinant of metabolic syndrome, and particularly of dyslipidemia, in this population.

The insulin gene variable number tandem repeat class I/III polymorphism is in linkage disequilibrium with birth weight but not Type 2 diabetes in the Pima population

The insulin gene variable number tandem repeat (INS-VNTR) is proposed to exert pleiotropic genetic effects on birth weight and diabetes susceptibility. In our study, we examined the influence of a polymorphism in tight linkage disequilibrium with INS-VNTR (-23Hph1) on birth weight and type 2 diabetes in the Pima population. A parent-offspring "trio" design was used to assess parent-of-origin effects and population stratification. The presence of the -23Hph1 T-allele was associated with lower birth weight (n = 192; -140 g per copy of the T-allele; P = 0.04), even after adjustment for effects of population stratification (P = 0.03). The effects of paternally transmitted T-alleles were greater than those of maternally transmitted alleles (paternally transmitted: -250 g, P = 0.05; maternally transmitted: -111 g, P = 0.43), but this difference was not statistically significant (P = 0.50). The -23Hph1 T-allele was associated with an increased prevalence of type 2 diabetes (P = 0.009), which family-based association analysis suggested was attributable to population structure (P = 0.04) without significant evidence of linkage disequilibrium between diabetes prevalence and genotype (P = 0.86). Thus allelic variation of the INS gene is associated with lower birth weight and increased prevalence of type 2 diabetes. Significant linkage disequilibrium was found between -23Hph1 and birth weight but not type 2 diabetes, an observation that supports a potential functional role of INS polymorphisms in the regulation of birth weight.

The insulin gene in diabetes

Lack of insulin production or abnormalities affecting insulin secretion are key to the development of almost all forms of diabetes, including the common type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes and the more rare forms of maturity-onset diabetes of the young (MODY). Because insulin has such a central role in the pathogenesis of both forms of diabetes, the insulin gene (INS) has always been considered a candidate susceptibility gene. A number of studies have shown that the allelic variation and parent-of-origin effects affect the transmission and expression of the insulin gene in pancreatic beta-cells and extra-pancreatic tissues. These observations have led to the formulation of new hypotheses to explain the biological mechanisms by which functional differences in the expression of the insulin gene may contribute to diabetes susceptibility.

Non-insulin-dependent diabetes mellitus--a collision between thrifty genes and an affluent society

Non-insulin-dependent diabetes mellitus (NIDDM) is one of the most common non-communicable diseases in the world. It has become obvious that NIDDM is the result of a collision between thrifty genes and an affluent society. Genes predisposing to NIDDM might have been survival genes for our ancestors, helping them to store energy during long periods of starvation. When these genes are exposed to a sedentary lifestyle and high caloric intake typical to the Western world, they predispose to obesity and insulin resistance. NIDDM results when beta cells cannot compensate for insulin resistance by increasing insulin secretion. Therefore, at least two inherited defects can be expected in NIDDM, one causing obesity and insulin resistance and the other inability to increase insulin secretion. In reality there may be more inherited defects. It has become quite clear that diabetes cannot simply be divided into NIDDM and insulin-dependent diabetes mellitus (IDDM). The disease is more heterogeneous; unmasking this heterogeneity and identifying new subgroups of diabetes presents a challenge to modern molecular biology.

Human type 1 diabetes and the insulin gene: principles of mapping polygenes

We review the strategy used to identify a susceptibility locus (IDDM2) for type 1 (insulin dependent) diabetes mellitus. As type 1 diabetes is becoming the paradigm for dissecting multifactorial disease genetics, the approach described provides important general guidelines for positional cloning of human disease polygenes. Main topics include: (a) historical conspectus of the mapping and identification of IDDM2--a critical survey of the work leading up to the conclusion that IDDM2 most likely corresponds to allelic variation at the insulin gene minisatellite (VNTR) locus; (b) the nature of allelic (length and sequence) variation at the VNTR locus; (c) gene interactions and disease pathogenesis; (d) mechanism of action of the INS VNTR in type 1 diabetes--insulin gene expression, parent-of-origin effects (genomic imprinting); and (e) summary and future prospects--alleles of the insulin VNTR that are protective for type 1 diabetes appear to encode susceptibility to type 2 diabetes.

Genetics of non-insulin-dependent (type-II) diabetes mellitus

Both genetic and environmental factors contribute to the etiology of non-insulin-dependent diabetes. The genetic component is heterogeneous and in some patients is probably complex, involving multiple genes. Specific genetic defects have been identified for rate monogenic forms of NIDDM: maturity-onset diabetes of the young, or MODY (which is due to glucokinase mutations in about 40% of families), syndromes of extreme insulin resistance (which often involve the insulin receptor), and diabetes-deafness syndromes (with defects in mitochondrial genes). In contrast, the genes involved in common forms of NIDDM are still uncertain. Mutations have been extensively searched in genes regulating insulin signaling and secretion. Some evidence of involvement has been produced for insulin-receptor substrate-1, glycogen synthase, the glucagon receptor, a ras-related protein (Rad), histocompatibility antigens, PC-1, and fatty acid binding protein, but the contributions of these genes to NIDDM is probably small. Other candidate genes (e.g. insulin, insulin receptor, glucose transporters) have been excluded as major diabetogenes. New insights are expected in the near future from the systematic scanning of the genome for linkage with NIDDM.

Linkage analysis does not support a role for glucokinase gene in the aetiology of type 2 diabetes mellitus among north western Italians

The contribution of a 3' glucokinase gene polymorphism to the aetiology of type 2 diabetes mellitus was studied in 17 diabetic pedigrees from North-Western Italy; linkage methodology was used. A CA repeat sequence was employed as a marker and amplified by PCR. Three alleles were found: Z (195 bp), Z + 4 (199 bp) and Z + 10 (205 bp). Since in diabetic families linkage analysis gave values of LOD score between -0.000438 and 0.026, the association between GK polymorphism and type 2 diabetes could not be either excluded or accepted. Based on these data, we conclude that glucokinase polymorphism is not a major determinant of type 2 diabetes mellitus, at least in our population, but, consistent with LOD score obtained, in some pedigrees it could assume a minor role in the aetiology of this disease.

Pima Indians as a model to study the genetics of NIDDM

More than half the Pima Indians over 35 years of age have non-insulin dependent diabetes mellitus (NIDDM). They have been the focus of prospective epidemiologic and metabolic studies for over two decades and the data collected during these studies are now proving invaluable in efforts to find genetic markers for NIDDM in humans. The Pima Indian model of this disease affords two major advantages. The population is genetically homogeneous compared to Caucasian populations, and therefore the causes of NIDDM are less heterogeneous, simplifying genetic linkage studies. Equally important, based on results from metabolic studies, two pre-diabetic phenotypes have been identified in the Pimas: insulin resistance and a low metabolic rate. Use of these phenotypes in genetic linkage analyses should greatly improve chances of finding genetic markers for NIDDM since these phenotypes may be more closely related to the putative abnormal gene products, and actual disease genes, than is the hyperglycemia of the fully developed phenotype of NIDDM.

HLA-DR and the 5' insulin gene polymorphism in insulin-dependent diabetes

While the human leukocyte antigen (HLA) region provides the major susceptibility for insulin-dependent (type I) diabetes mellitus (IDDM), other (non-HLA) genes must also play a role. Population studies have shown an increased frequency of small insertions (class I alleles) 5' to the insulin gene in individuals with IDDM, suggesting that this region may account for part, if not all, of the non-HLA genetic predisposition. However, no data are available as to whether the relation of the insulin gene polymorphism is to a DR-defined subset of IDDM or with all of IDDM. To test the hypothesis that specific combinations of HLA and insulin gene polymorphism alleles may interact in providing susceptibility for IDDM, HLA-DR and 5' insulin gene insertion size have been determined in 300 individuals with IDDM. The frequency of class 1 insulin gene alleles in the entire sample is 0.79 and the frequency of class 3 alleles (large inserts) is 0.20. The frequencies of class 1 alleles were equal across all DR classes: 0.79 in the DR3/X IDDM subjects, 0.80 in the DR4/X, 0.79 in the DR3/4, and 0.78 in those with DRX/X. Additionally, the frequencies of class 1/1 homozygotes and 1/3 heterozygotes were similar between HLA-DR types. These results suggest that the HLA region and the region 5' to the insulin gene provide independent and nonsynergistic genetic risks for IDDM.

Non-HLA region genes in insulin dependent diabetes mellitus

The focus of this chapter is on the contribution of genes outside the HLA region to insulin dependent diabetes mellitus (IDDM) susceptibility. We review laboratory evidence for such genes from published studies and also present unpublished data from our recent research. The existence of genes predisposing to IDDM in the region of the insulin (INS) gene now appears established. Association analysis has demonstrated an increased frequency of class 1 alleles of the 5' INS polymorphism in diabetics compared with controls, and a new method of analysis (AFBAC) has shown that this association is not an artefact of population stratification. Interestingly, the effect of INS region susceptibility on IDDM cannot be detected by linkage analysis, suggesting that if a genetic marker locus is close to a disease susceptibility locus, association analysis may be a more sensitive method than linkage analysis for detecting the susceptibility locus. There is no convincing evidence that genes in the T cell receptor beta chain (TCRB) or alpha chain (TCRA) regions influence predisposition to IDDM, either directly, or indirectly through interaction with HLA region genes. However, we present new evidence for interaction between TCRB and immunoglobulin heavy chain (Gm) region genes in IDDM: diabetics who are positive for the IgG2 allotype G2m(23) have significantly different frequencies of a TCRB restriction fragment length polymorphism (RFLP) than those who are negative for the allotype. Gm region genes also appear to have indirect effects on IDDM susceptibility through interaction with HLA and INS region genes: DR3/4 and non-DR3/4 diabetics have significantly different frequencies of G2m(23), and INS1/1 and non-INS1/1 diabetics also have significantly different frequencies of this allotype. To our knowledge, there are no other studies of Gm-TCRB or Gm-INS interaction in IDDM susceptibility. Evidence for Gm-HLA interaction in IDDM has been published by several other groups of investigators, however the specific phenotypic interaction effects reported have differed. Nevertheless, pooled data from three studies of Gm/HLA haplotype segregation in affected sib pairs shows significantly increased sharing of Gm haplotypes in affected pairs who share both HLA haplotypes. The biological mechanisms underlying the direct (HLA, INS) and indirect (Gm-TCRB, Gm-HLA, Gm-INS) effects of these genetic regions on IDDM susceptibility remain to be elucidated.

Genetics of non-insulin dependent diabetes mellitus

It is probable that NIDDM has a multifactorial origin in which environmental factors hasten the progression of the disease in genetically predisposed individuals. The importance of the genetic contribution to NIDDM has been established by the study of certain inbred populations, the almost 100% concordance of disease in monozygotic twins and by familial clustering. However, progress in identifying specific genetic factors involved in NIDDM has been slow and no consistent evidence has emerged supporting a major aetiological role for any of the genes so far studied. This may be due in part to methodological problems encountered in the identification of such disease susceptibility genes.

Polymorphism in 5' flanking region of human insulin gene. Relationships with atherosclerosis, lipid levels, and age in three samples from Denmark

Variations in the DNA sequence flanking the 5' region of the human insulin gene (U- and L-alleles) were studied in relation to atherosclerosis, lipid levels, and age in three groups of atherosclerotic individuals and in nonatherosclerotic controls. The atherosclerotic groups comprised a postmyocardial infarction group with a mean age of 48 years, a group of individuals operated on for carotid stenosis with a mean age of 62 years, and a group of 85-year-olds with clinical coronary disease, peripheral arterial disease, or both. All 331 individuals were unrelated Caucasians of Danish ancestry. There were no significant differences (p greater than 0.05) in genotype distribution or allele frequencies between atherosclerotic and nonatherosclerotic individuals, but in the 85-year-olds, there was evidence (p less than 0.10) for a lower U-allele frequency in nonatherosclerotic women compared to atherosclerotic women. In nonatherosclerotic women, there was a significant decrease in U-allele frequency with age (60 to 85 years). This decrease does not prove conclusively, but is compatible with, the hypothesis that the U-allele predisposes to, or the L-allele protects against, atherosclerosis. The possible effect of the U-allele on the development of atherosclerosis does not seem to be mediated through conventional risk factors.

DNA length polymorphism 5' to the myelin basic protein gene is associated with multiple sclerosis

A site of DNA polymorphism linked to the myelin basic protein gene, identified as restriction fragment length polymorphism, was analyzed in a population-based study comparing patients with clinically definite multiple sclerosis (MS) and population-matched control subjects. A 0.9-kilobase (kb) genomic DNA fragment (EcoG) encompassing the first exon of the human myelin basic protein gene, located on the long arm of chromosome 18, identified ten alleles arising from a region of DNA, 1.5 kb 5' to the myelin basic protein gene first exon coding region. Produced by RsaI digests and ranging in length from 2.05 to 2.15 kb, these alleles vary in size by up to 100 base pairs due to insertion or deletion, or both, from a 1-kb length of repetitive DNA. Allele frequencies among 65 patients with MS were compared with those of 63 control subjects. Chi square for these data was significant (p less than 0.001), largely due to a preponderance in the patients with MS of alleles in the 2.14- to 2.15-kb range. Comparison of the numbers of patients with MS and control subjects bearing specific alleles showed that 45% of the patients carried at least one allele of 2.14 to 2.15 kb as opposed to 19% of control subjects (p less than 0.005). These data, while preliminary, suggest that patients with MS differ from population-matched control subjects with respect to DNA polymorphism linked to the myelin basic protein gene. Although no pathogenic relationship between this polymorphism and MS can be presupposed, this finding raises the possibility that the myelin basic protein gene or some other myelin basic protein-linked locus may be a factor in susceptibility to MS.

[Physiopathology of non-insulin-dependent diabetes: current data and therapeutic consequences]

Non insulin-dependent diabetes mellitus results from the combination in varying proportions of low plasma insulin levels (insulinopenia), peripheral resistance to insulin and increased hepatic glucose production. Abnormalities of insulin secretion can be demonstrated without and after stimulation. Insulin resistance mainly occurs in skeletal muscle and is primarily due to a "postreceptor" defect. A pancreatic peptide, amylin, may participate in insulin resistance. Hepatic glucose production correlates with high fasting plasma glucose concentrations. Whatever its initial mechanism, hyperglycaemia maintains low insulin secretion and insulin resistance by its toxicity. In the light of these data, the effects of weight loss in obese non insulin-dependent diabetics have become clearer. The action of biguanides on insulin sensitivity is confirmed. Sulphonylureas have a pancreatic and an extrapancreatic action. The normoglycaemia obtained by intermittent insulin therapy can break the vicious circle of glucose toxicity. The use of prolonged insulin therapy is discussed. Finally, new compounds with an original mode of action offer hopes for the future.

A lack of genetic linkage of renin gene restriction fragment length polymorphisms with human hypertension

Because renin is an important enzyme in blood pressure regulation, we studied the possibility that an alteration in the structure of the human renin gene is genetically linked to human essential hypertension or associated with levels of plasma renin activity or blood pressure. By using specific DNA probes, we have identified four polymorphisms in the human renin gene with the restriction enzymes Taq I, HindIII, Bgl I, and Bgl II. The gene location of all of these polymorphisms except for the Bgl II polymorphism has been determined, and their frequencies were initially estimated in a population of 50 random subjects. To test the clinical significance of these polymorphisms, we studied 68 persons from a large Utah pedigree with a high incidence of hypertension. Among nine relatives with hypertension, genetic linkage without recombination was ruled out by observing several obligate recombinants. We also found no significant association of the restriction fragment length polymorphisms with quantitative measurements of sitting or standing, systolic or diastolic blood pressures, or plasma renin activity in 59 untreated members of this pedigree. Although we found no genetic linkage in this set of study subjects, the characterization of the restriction fragment length polymorphisms for the renin gene may be useful in future studies of other selected pedigrees for the presence of one or more of these to be a genetic marker in hypertension.

Polymorphism in the 5'-flanking region of the insulin gene and its potential relation to cardiovascular disease risk: observations in a biracial community. The Bogalusa Heart Study

The gene frequencies of a polymorphism in the 5'-flanking region of the insulin gene and its relationship to cardiovascular disease risk were studied in a well defined population of children (mean age 5.5 years) from a biracial community. The BglII endonuclease was used for digestion of the DNA around this polymorphic region. The risk factors studied included parental and grandparental self-reported histories of myocardial infarction and diabetes mellitus, fasting glucose and insulin levels, lipoprotein, cholesterol, and triglyceride levels, and skinfold thicknesses and weight. Four alleles were observed at this locus, with the class 2 allele being significantly more common among blacks than whites. Among white children, the class 3 allele was associated with increased risk for grandparental diabetes mellitus. White children with 2 copies of the class 3 allele had significantly higher levels of glucose. Black children with a copy of the class 3 allele had significantly higher levels of insulin. This study indicates that the class 3 allele is potentially associated with risk for diabetes mellitus and coronary heart disease that can be observed in childhood.

Coronary artery disease, HDL cholesterol, and insulin-gene flanking sequences

The relationship between coronary artery disease, HDL cholesterol, and the hypervariable region flanking the human insulin gene was studied in Saudi Arabian non-diabetic subjects (n = 68) and in patients with Type 2 diabetes (n = 35). A locus of insulin-gene-linked DNA polymorphism with three average size classes of alleles was found: a small class 1, a rare medium size class 2, and a large class 3 allele. In the total group of subjects (n = 103), those with the class 3 allele had a lower plasma HDL cholesterol concentration than those without the class 3 allele (0.93 +/- 0.26 vs 1.12 +/- 0.30 mmol l-1, 2p less than 0.003). No difference in genotype and allelic frequency was found between patients with and without coronary artery disease in the combined group of subjects, with and without diabetes. Similarly the genotype distribution was not different between non-diabetic subjects and patients with Type 2 diabetes in the combined group of subjects, both with and without coronary artery disease. In conclusion, the study did not confirm a previous study showing an association between the class 3 allele and atherosclerosis in a Caucasian population. However, the class 3 allele was associated with a low plasma HDL cholesterol concentration.

The insulin gene and susceptibility to IDDM

The association between insulin-dependent diabetes mellitus (IDDM) and an allele of a restriction fragment length polymorphism (RFLP) 5' to the coding region of the insulin gene has raised the possibility that variation in the vicinity of the insulin gene confers susceptibility to IDDM. To test this hypothesis, the distribution of insulin gene sharing in affected sib pairs (ASPs) from the Genetic Analysis Workshop 5 (GAW5) families has been compared with that expected on the basis of random assortment. There is no deviation from random expectation in insulin gene sharing among 95 ASPs from families fully informative for the insulin gene. This is also true when insulin gene sharing is conditioned on HLA sharing, on the particular HLA DR types in ASPs, or on the parents' insulin allele classes. These results thus provide no evidence that variation at or near the insulin gene confers susceptibility to IDDM. However, we also used computer simulation to investigate how the insulin gene region could contribute susceptibility to IDDM without yielding evidence for distortion in insulin gene sharing in a sample comparable to that of GAW5. We found that various levels of insulin gene involvement in IDDM could generate a population association between the insulin gene RFLP and IDDM comparable to that reported in the literature, without producing significant distortion in insulin gene sharing of ASPs.

Polymorphism at the 5' end flanking region of the insulin gene is associated with reduced insulin secretion in healthy individuals

Sixty-four unrelated healthy subjects were studied for the detection of a DNA polymorphism at the 5' end of the insulin gene. No significant difference between the groups was found in blood glucose values at fasting and after an oral glucose load. A significant association was found between fasting (P less than 0.05) and after load plasma C-peptide levels (P less than 0.01) and the presence of a 1.6 Kb insertion at the 5' end of the insulin gene. A gene dose-dependent effect was noted, class 3/3 individuals having the lowest after-load C-peptide concentration and class 1/3 an intermediate level (F for the linear trend: P = 0.007). This might suggest that insulin gene polymorphism affects insulin secretion in healthy individuals. In order to confirm this, a subgroup of six class 3/3 and eight class 1/1 individuals subsequently underwent a hyperglycaemic clamp. The tissue sensitivity to insulin was similar in the two groups but glucose-stimulated insulin secretion was markedly impaired in homozygotes for the class 3 allele. In this group, insulin secretion was, on average, only one-third of that in class 1/1 individuals (P less than 0.02). Similarly impaired in class 3/3 persons was the glucose + arginine-stimulated insulin secretion (P less than 0.05). We conclude that the polymorphism at the 5' end of the insulin gene is associated with variations in insulin secretion in healthy humans.

The load of genetic and partially genetic diseases in man. II. Some selected common multifactorial diseases: estimates of population prevalence and of detriment in terms of years of lost and impaired life

This paper presents epidemiological data on the prevalence of 26 common (i.e., having a lifetime prevalence of more than 1 per 10(4) individuals in the population) multifactorial diseases in Hungary and estimates of detriment associated with them. The detriment is expressed using 3 indicators, namely years of lost life (LL), potentially impaired life (PIL) and actually impaired life (AIL). The total prevalence of these diseases in Hungary has been estimated to be about 6500 per 10(4) individuals in the population. This estimate is in agreement with published data for other parts of the world. On the basis of clinical severity, these diseases have been split into 3 groups, namely (1) very severe (schizophrenia, multiple sclerosis, epilepsy, acute myocardial infarction and related conditions, and systemic lupus erythematosus); (2) moderately severe and/or episodal or seasonal (15 entities including Graves' disease, diabetes mellitus, gout, affective psychoses, essential hypertension, peptic ulcers, asthma, etc.); and (3) less severe than those in the first 2 groups (varicose veins, allergic rhinitis, atopic dermatitis, Scheuermann disease and adolescent idiopathic scoliosis). The essential clinical and genetic aspects of these diseases are briefly discussed. With the exception of epilepsy, none of the diseases included in our list causes mortality between ages 0 and 19. However, they are among the leading causes of death between ages 20 and 69 and thereafter. A sizeable proportion of those with essential hypertension, diabetes mellitus, rheumatoid arthritis, etc. survive to 70 years and beyond, as do those with gout, glaucoma, allergic rhinitis, psoriasis, etc. Overall, about 16% of all deaths that occur in Hungary every year (all age groups) can be attributed to these diseases. The mean number of years of PIL covers a wide range (about 20-40, 12-70 and 40-60 for groups 1, 2 and 3, respectively), the overall mean being about 24 years. However, the nature and degree of impairment and the impact on the life quality of those afflicted differ for the different diseases. Likewise, the mean number of years of AIL (for which the interval between the mean age at premature retirement and mean age at death was used as a rough index) also spans a wide range from 16 to 45, and the overall mean is about 20 years. At the population level, the diseases considered in this paper cause about 2700 years of LL, 96,000 years of PIL and about 5800 years of AIL per 10(4) individuals in the population. Relative to Mendelian diseases as a whole, these multifactorial diseases are associated with much greater detriment (LL: 1.4 X; PIL: 30 X and AIL: 3.9 X).

Identification of a variant growth hormone haplotype in mice selected for high body weight

Restriction site analysis revealed a variant growth hormone gene haplotype fixed within growth-selected mice (High line-3; HL-3) exhibiting growth rates 1·5 times greater than those of unselected Foundation population (FP-3) mice. Relative to the FP-3 haplotype, the HL-3 haplotype exhibited restriction fragment length polymorphisms for each of seven different restriction enzymes. Three of the polymorphic sites lie within 1·1 kb of the 5′ end of the structural gene; a fourth polymorphism exists within the structural gene. The HL-3 haplotype was also fixed within an additional three growth-selected lines (including a replicate of HL-3). This identification of an association, between the natural variant of a growth regulating gene and a growth-related phenotype, is the prototype of experiments that could lead to the isolation of variant genes which enhance livestock production characters.

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.

Aetiology. Non-insulin-dependent diabetes

NIDDM appears to be a disease of complex aetiology. Although specific genetic markers for the disease have yet to be defined, there is clear evidence for genetic predisposition, with high concordance in monozygous twins. However, concordance is incomplete, and there are therefore additional, non-genetic, mechanisms which are responsible for increasing the risk of the disease in susceptible subjects. At the present time, the most plausible environmental precipitants appear to be the inter-related triad of obesity, low levels of habitual physical exercise and diet. The power of environmental determinants, and their interaction one with another, may also be subject to individual genetic determination, and may not act in a similar manner in all populations. Some non-Caucasian populations, which have undergone marked sociocultural change, are now extremely susceptible to NIDDM. This is probably the result of evolutionarily heightened genetic predisposition, compounded by strong environmental influence resulting from the recent changes in their human ecology. Since prevalence is strongly related to age, NIDDM also represents a growing problem to the world's industrialized societies, for many of which longevity is now the major demographic trend. Research into the aetiology of NIDDM must not only continue, it must also explore new directions, and attain greater scientific depth and sophistication, if it is to make a useful contribution to the eventual prevention and control of the disease.

DNA polymorphism and the study of disease associations

Recombinant DNA approaches to disease analysis may be as applicable to studies of disease association as they are to the analysis and diagnosis of single-gene defects. Population and/or family association analyses, using restriction fragment length polymorphisms around candidate genes as markers, have been employed to study conditions such as atherosclerosis and disease with an HLA-association. Progress made to date in disease-association studies using recombinant DNA methodology is reviewed, the rationale behind such studies is examined and associated problems and pitfalls discussed.

Restriction fragment length polymorphisms of the insulin gene hypervariable region in gestational onset diabetes mellitus

Restriction fragment length polymorphisms in the insulin gene hypervariable region are compared among 93 women with gestational onset diabetes mellitus and 146 women with normal glucose tolerance during pregnancy. No significant differences in gene or genotype frequencies were observed in the overall sample (p greater than 0.50). However, an increased frequency of one allele (class 1) was observed among nonoverweight patients with gestational onset diabetes mellitus with elevated fasting plasma glucose levels compared with age-, race-, and parity-matched control subjects (p = 0.061). These data suggest that gestational onset diabetes mellitus is a heterogeneous disorder with respect to both genotypic and phenotypic characteristics, and that restriction fragment length polymorphisms near the insulin gene may serve as a molecular marker for susceptibility to gestational onset diabetes mellitus only in some women.

A genetic analysis of type 2 (non-insulin-dependent) diabetes mellitus in Punjabi Sikhs and British Caucasoid patients

A genetic analysis of diabetic and non-diabetic Punjabi Sikhs (n = 164) was made for markers of non-insulin-dependent diabetes mellitus using insulin receptor, insulin, and HLA-D alpha chain gene probes. Additionally British Caucasoids (n = 163) were studied using the insulin receptor probe. Insulin receptor gene restriction fragment length polymorphisms were defined using Southern blot techniques and the restriction enzyme Bgl II and BAm Hl. In Punjabi Sikhs and British Caucasoids neither of the restriction fragment length polymorphisms distinguished non-insulin-dependent diabetes mellitus subjects from controls. In the Sikhs no association with non-insulin-dependent diabetes mellitus was seen with the hypervariable region of the insulin gene or with HLA-DR/DQ/DX alpha chain restriction fragment length polymorphisms. We therefore conclude that despite the high prevalence of non-insulin-dependent diabetes mellitus in Asians we were unable to find any genetic markers for this disease using the available cloned gene probes.

Functional hemizygosity in the human genome: direct estimate from twelve erythrocyte enzyme loci

Cord blood samples from 2020 unrelated newborns were screened for levels of enzyme activity for twelve enzymes. The level of enzymatic activity for 100 determinations were consistent with the existence of an enzyme-deficiency allele. The frequency of deficiency alleles in the Black population (0.0071) was four times higher (after removal of the G6PD*A- variant) than in the Caucasian sample (0.0016). These frequencies are approximately double the frequency of rare electrophoretic mobility variants at similar loci in the same population. Given the number of functionally important loci in the human genome, these enzyme deficiency variants could constitute a significant health burden.

Clonal analysis of human colorectal tumors

The clonal composition of human colorectal tumors was studied by means of restriction fragment length polymorphisms (RFLPs). First, X-linked RFLPs were used to examine the pattern of X chromosome inactivation in colorectal tumors of females. All 50 tumors examined showed monoclonal patterns of X chromosome inactivation; these tumors included 20 carcinomas as well as 30 adenomas of either familial or spontaneous type. Second, RFLPs of autosomes were used as clonal markers to detect the somatic loss or gain of specific chromosomal sequences in colorectal tumors. Among other changes, it was found that somatic loss of chromosome 17p sequences occurred in over 75 percent of the carcinomas examined, but such loss was rare in adenomas. These data support a monoclonal origin for colorectal neoplasms, and suggest that a gene on the short arm of chromosome 17 may be associated with progression from the benign to the malignant state.

DNA polymorphisms of apolipoprotein A-I/C-III and insulin genes in familial hypertriglyceridemia and coronary heart disease

Two DNA polymorphisms adjacent to the apolipoprotein A-I/C-III and insulin genes have been suggested to be associated with hypertriglyceridemia and increased risk of coronary heart disease. Using cloned apolipoprotein A-I and insulin gene probes, we determined the genotypes of 39 subjects from six different kindreds with familial clustering of hypertriglyceridemia, 20 additional unrelated subjects with hypertriglyceridemia, 39 patients with angiographically confirmed coronary heart disease (CHD) and 61 normolipemic control subjects. The S2 allele bearing an additional SstI restriction site in the apo A-I/C-III complex was found in 16% of healthy controls, 23% of patients with CHD and 62% (P less than 0.001 when compared to controls) of unrelated subjects with hypertriglyceridemia. Among CHD patients the S2 allele was present in 6 out of 14 hypertriglyceridemic patients but only 3 out of 25 normotriglyceridemic patients (P less than 0.05). The S2 allele was present in 64% of subjects from kindreds with hypertriglyceridemia but this allele did not determine the occurrence of hyperlipidemia. The frequencies of the large size or U allele of the polymorphic DNA region flanking the 5' end of the insulin gene in CHD patients (33%) and in controls (24%) were not significantly different. Neither of the polymorphisms studied was associated with changes in serum LDL or HDL cholesterol levels in patients with CHD or unrelated subjects with hypertriglyceridemia. The data suggest that, at least in the Finnish population, the S2 allele of the apolipoprotein A-I/C-III gene complex may serve as a genetic marker for hypertriglyceridemia, whereas both DNA polymorphisms studied are probably useless in determining individual risks of atherosclerosis.

Some trends in medical populations genetics

Five topics concerning medical population genetics have been selected for discussion: in the field of population cytogenetics, the frequency of chromosomal aberrations and the roles of mutation and selection in the maintenance of balanced rearrangements are studied; the long term genetic effects of treatment and prevention of genetic diseases are reviewed; the relationships between malaria and the sickle-cell trait are discussed; some recent works concerning human DNA polymorphisms in the field of population genetics are presented, and finally, some methods of genetic epidemiology are described.

A study into possible deviation from the Hardy-Weinberg equilibrium by the alleles of the hypervariable sequence in the region of the human insulin gene

A number of studies have reported on possible relationships between a hypervariable sequence near the 5' end of the insulin gene and some common diseases. Control populations within these studies appear to disobey the Hardy-Weinberg equilibrium. In this study we have ascertained the allele frequencies in 181 random individuals. The chi-squared statistic comparing this population with a theoretical Hardy-Weinberg population was 0.61. This makes it unlikely that in the general population the Hardy-Weinberg rule is disobeyed. Possible reasons for the discrepancy between our study and the studies of others are discussed.

Genetic aspects of arteriosclerosis

This review discusses the genetic factors in the development of arteriosclerosis and coronary heart disease (CHD). In several studies, multivariate analysis of prospective mortality/morbidity data and angiographic findings have indicated that a family history of CHD contributed to CHD risk independently of the established risk factors. In addition, ethnic groups that differ in the prevalence and incidence of CHD also markedly differ in blood groups and protein-enzymatic markers. These or other genetic differences may affect CHD rates. Data from fraternal and identical twins, the source of some early genetic CHD findings, are reviewed. Genetic disorders of lipoprotein metabolism and transport, such as familial hypercholesterolemia, as well as other monogenic disorders are discussed. The role of apoprotein E polymorphism i other monogenic disorders are discussed. The role of apoprotein E polymorphism in determining plasma LDL variability among individuals is considered. Recombinant DNA technology, molecular cloning, and the identification of restriction fragment length polymorphisms are new tools for investigators who assess DNA polymorphism. Recent advances in that domain include: DNA polymorphisms affecting blood levels of apo A-I and A-II, association of a DNA insertion on chromosome 19 with severe premature atherosclerosis, and information concerning linkage of the genes for various apolipoproteins. In addition, the evidence for a major genetic component in diabetes mellitus and research into the genetic aspects of hypertension are reviewed. The male/female ratio in pathologically and epidemiologically assessed atherosclerosis may provide clues to the role of genetics. Early structural changes in the coronary artery intima are compatible with the ethnic and gender predilection. A key question in understanding underlying mechanisms in atherosclerosis is why coronary arteries are occluded in individuals whose other arterial systems are largely unaffected. The review concludes with a discussion of the directions and implications of future genetic research in arteriosclerosis with an emphasis on uncovering genetically determined differences in arterial wall response to blood flow. Subpopulations with different genetic risks may be identified, in which case universal preventive strategies might be replaced with specific ones.

High frequency of class 3 allele in the human insulin gene in Japanese type 2 (non-insulin-dependent) diabetic patients with a family history of diabetes

The restriction fragment length polymorphism in the 5' flanking region of the human insulin gene was studied in 155 nonobese Japanese subjects. The subjects consisted of 36 Type 2 (non-insulin-dependent) diabetic patients with a family history of diabetes mellitus, 42 Type 2 diabetic patients without a family history of diabetes, 42 Type 1 (insulin-dependent) diabetic patients, and 35 healthy volunteers who served as control subjects. It was demonstrated that, in Japanese healthy subjects and diabetic patients, the incidence of the insertion into 5' flanking region of the insulin gene was found to be significantly lower (p less than 0.05) than those in Caucasians and other races already investigated. Even though the class 3 gene allelic frequency in Type 2 diabetic patients without a family history of diabetes (0.060) was not higher than that in healthy subjects (0.014), in nonobese Type 2 diabetic patients with a family history of diabetes the allelic frequency of the inserted class 3 gene (0.111) was found to be significantly higher (p less than 0.02) than that in control subjects. These data suggest that the insulin gene polymorphism relates to the aetiology of diabetes mellitus.

Diagnosis of genetic disease using recombinant DNA

Recombinant DNA technology promises to make an important contribution to the analysis and diagnosis of inherited human disease. Direct detection and analysis of various genetic defects at the DNA level are now possible using cloned gene or oligonucleotide probes. In addition, the use of restriction fragment length polymorphisms associated with linked DNA segments should permit not only the diagnosis of hitherto undetectable disease states but also the chromosomal localization of the loci responsible. The eventual isolation of disease loci should lead to a better understanding of the molecular basis of inherited disease.