Population based study of prevalence of islet cell autoantibodies in monozygotic and dizygotic Danish twin pairs with insulin dependent diabetes mellitus

The impact of disease characteristics on multiple sclerosis patients' quality of life

OBJECTIVES

The aim of this study was to assess the quality of life (QoL) of patients with multiple sclerosis (MS), and to investigate the effects of characteristics of MS such as disease course, severity, and relapses on patients' QoL.

METHODS

This was a cross-sectional study, in which 171 patients were enrolled. Health-related QoL was assessed using the Persian version of the Multiple Sclerosis Quality of Life-54 questionnaire. To measure patients' disability status, we used the Expanded Disability Status Scale. Other variables included in the study were disease course and relapses of the disease.

RESULTS

The average scores for patients' physical and mental QoL were 60.9±22.3 and 59.5±21.4, respectively. In a bivariate analysis, disease course, severity of the disease, and relapses were significantly associated with the physical and mental health composite scores. In a hierarchal regression analysis, disease course, severity of the disease, and relapses were responsible for 38 and 16% of the variance in physical and mental QoL, respectively. It was also observed that relapses were a strong predictor of both physical and mental QoL.

CONCLUSIONS

Our results showed that disease characteristics significantly affected both dimensions of QoL. It is therefore suggested that health care providers should be aware of these characteristics of MS to more successfully improve MS patients' QoL.

Risk factors and primary prevention trials for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease resulting in the designated immune destruction of insulin producing β-cells, usually diagnosed in youth, and associated with important psychological, familial, and social disorders. Once diagnosed, patients need lifelong insulin treatment and will experience multiple disease-associated complications. There is no cure for T1DM currently. The last decade has witnessed great progress in elucidating the causes and treatment of the disease based on numerous researches both in rodent models of spontaneous diabetes and in humans. This article summarises our current understanding of the pathogenesis of T1DM, the roles of the immune system, genes, environment and other factors in the continuing and rapid increase in T1DM incidence at younger ages in humans. In addition, we discuss the strategies for primary and secondary prevention trials of T1DM. The purpose of this review is to provide an overview of this disorder's pathogenesis, risk factors that cause the disease, as well as to bring forward an ideal approach to prevent and cure the disorder.

The Influence of Zygosity and Chorion Type on Fat Distribution in Young Adult Twins Consequences for Twin Studies

An adverse intra-uterine environment has been associated with abdominal fat distribution in singletons. Twins often have a low birth weight and a short gestation. Therefore, they may have an increased risk to develop abdominal obesity. Furthermore, monozygotic monochorionic twins (MZ MC) have a larger intra-pair birth weight difference compared to monozygotic dichorionic twins (MZ DC). If adult anthropometry is programmed in utero, this may affect the intra-pair correlations in adulthood and, consequently, also the results from the classic twin method to estimate genetic and environmental influences. In the present study, we compared the absolute values, the intra-pair differences, and the intra-pair correlations of body mass, height, BMI, and abdominal fat distribution of 424 MZ MC, MZ DC and dizygotic (DZ) twin pairs (aged 18–34 yrs). DZ, MZ DC and MZ MC twins did not differ for most anthropometric characteristics. Only MZ women tended (p = 0.03) to accumulate more abdominal fat compared to DZ twins. Overall, the contribution of zygosity and chorion type to adult anthropometry was rather low (≤ 1.7%). Although the intra-pair birth weight difference of MZ MC pairs (10.5% in men, 12.3% in women) was significantly larger compared to that of MZ DC pairs (6.9% and 9.2% resp.), the intra-pair differences in adult anthropometry were similar for both MZ twin types. Also the intra-pair correlations of MZ MC and MZ DC pairs were strikingly alike, suggesting no significant influence of the prenatal environment on adult concordance. In conclusion, the substantial difference in the prenatal environment of MZ MC and MZ DC twins did not result in a difference in intra-pair concordance of adult anthropometry and fat distribution. Therefore, we suggest that the chorion type of MZ twins does not bias the twin design and the estimation of the genetic contribution to adult anthropometry.

Rotavirus infections and development of type 1 diabetes: an evasive conundrum

Type 1 diabetes (T1D) is an organ-specific autoimmune disease caused by altered immune tolerance to specific proteins leading to a selective destruction of insulin-producing beta cells in genetically predisposed individuals. T1D is likely to be triggered by environmental factors, including virus infections in genetically predisposed individuals. Rotaviruses are the main cause of severe diarrhea among children worldwide, but they seem to have a role also in T1D induction. Epidemiological data may be consistent with a similar hypothesis. Mechanisms hypothesized include molecular mimicry, bystander activation (with or without epitope spreading), and viral persistence. In this review the authors analyze the factors accounting for rotavirus ability to prime islet autoimmunity and cause T1D. A thorough comprehension of their potential pathogenetic mechanisms may allow preventive strategies to be designed.

Glutathione-s-transferase M1 and T1 polymorphisms and associations with type 1 diabetes age-at-onset

Type 1 diabetes (T1D) is an autoimmune disease characterized by pancreatic beta cell destruction involving auto-reactive T-cells, pro-inflammatory cytokines, reactive oxygen species (ROS) and loss of insulin. Monozygotic twin studies show a 20-60% concordance with T1D indicating there may be an environmental component to the disease. Glutathione (GSH) is the major endogenous antioxidant produced by the cell. GSH participates directly in the neutralization of free radicals and plays a role in the immune response. Glutathione-s-transferases (GSTs) conjugate GSH to free-radicals or xenobiotics. GST activity depletes GSH levels and may either detoxify or enhance the toxicity of a compound. Glutathione-s-transferase mu 1 (GSTM1) and glutathione-s-transferase theta 1 (GSTT1) have polymorphic homozygous deletion (null) genotypes resulting in complete absence of enzyme activity. GSTM1 and GSTT1 null genotypes in Caucasian populations have frequencies of approximately 40-60% and 15-20%, respectively. GST null genotypes have been associated with susceptibility to cancer and protection against chronic pancreatitis. The aim of this study was to investigate associations with GSTM1 and GSTT1 polymorphisms in a group T1D patients and control subjects 0-35 years old who participated in the Combined Swedish Childhood Diabetes Registry and Diabetes Incidence Study (1986-1988). Results show that the presence of the GSTM1 and not the null genotype (OR, 2.13 95% CI, 1.23-3.70, p-value, 0.007, Bonferroni corrected p-value, 0.035) may be a susceptibility factor in T1D 14-20 years old. These results suggest that the GSTM1 null genotype is associated with T1D protection and T1D age-at-onset and that susceptibility to T1D may involve GST conjugation.

Enteroviruses and type 1 diabetes

The development of type 1 diabetes mellitus (T1DM) has been linked to exposure to environmental triggers, with Enteroviruses (EV) historically considered the prime suspects. Early serological studies suggested a link between EV infections and the development of T1DM and, though controversial, have been bolstered by more recent studies using more sensitive techniques such as direct detection of the EV genome by RT-PCR in peripheral blood. In this review, we consider the weight of evidence that EV can be considered a candidate trigger of T1DM, using three major criteria: (1) is EV infection associated with clinical T1DM, (2) can EV trigger the development of autoimmunity and (3) what would explain the putative association?

Prediabetes in children: natural history, diagnosis, and preventive strategies

The clinical manifestation of type 1 diabetes mellitus is preceded by an asymptomatic prodromal period called prediabetes or preclinical diabetes. It may last from a few months to several years, during which the autoimmune destruction of the insulin-producing beta-cells in the pancreas progresses. The genes on the human leukocyte antigen (HLA) and insulin gene region are major genetic determinants for genetic disease susceptibility, while dietary compounds and viral infections are the most likely environmental factors contributing to the etiopathogenesis. T cells are thought to be the effector cells for the beta-cell destruction, and glutamic acid decarboxylase, insulinoma-associated protein 2 and insulin represent the three major autoantigens. Autoantibodies are early detectable markers of an ongoing disease process and are used to diagnose prediabetes. Among first-degree relatives of patients with type 1 diabetes, the risk for clinical disease can be graded from <5% in those with one or no antibodies to >90% in individuals who carry the HLA-DQB1*02/0302 risk genotype and are positive for multiple autoantibodies. beta-Cell function may also be tested in autoantibody-positive individuals and low first-phase insulin response is highly predictive for rapid progression to the clinical disease. However, dynamic course and individual variation of the disease process complicates the disease prediction, and it is not known whether all individuals with signs of prediabetes will inevitably progress to clinical type 1 diabetes. Until clinically applicable prevention for the condition exists, the screening for the risk markers of type 1 diabetes should actively be undertaken only in the context of research projects. Several major national and international multicenter studies are ongoing to test the potential of various agents (e.g. insulin and nicotinamide) or early elimination of dietary compounds (e.g. cow's milk proteins) to delay or prevent the onset of clinical type 1 diabetes.

Genetic epidemiology of type 1 diabetes

Family and twin studies indicate that a substantial fraction of susceptibility to type 1 diabetes is attributable to genetic factors. These and other epidemiologic studies also implicate environmental factors as important triggers. Although the specific environmental factors that contribute to immune-mediated diabetes remain unknown, several of the relevant genetic factors have been identified using two main approaches: genome-wide linkage analysis and candidate gene association studies. This article reviews the epidemiology of type 1 diabetes, the relative merits of linkage and association studies, and the results achieved so far using these two approaches. Prospects for the future of type 1 diabetes genetics research are considered.

Autoimmunity and familial risk of type 1 diabetes

There is evidence that the process leading to type I diabetes may start in early infancy or already in utero. Even though diabetes-associated antibodies can be detected in up to half of the pregnancies of mothers with type I diabetes, pregnancy itself has no major effect on these antibodies. If such antibodies are present in the mother, they are transferred to the fetal circulation and are detectable in cord blood. Most of the transplacentally transferred antibodies disappear by 6 months of age, but may persist even longer. Antibodies present in cord blood may represent true induction of beta-cell autoimmunity, but such a phenomenon is extremely rare. The offspring of affected mothers have a 2% to 3% risk of type I diabetes, which is about one third of that in the offspring of affected fathers. A novel conceivable explanation is that exogenous insulin transplacentally transferred in immune complexes might lead to the induction of tolerance to insulin, which may be the primary autoantigen in type I diabetes. The possible protective or predisposing effect of diabetes-associated antibodies detectable at birth on progression to clinical type I diabetes later will be assessed in ongoing prospective birth cohort studies.

Impact of genetic and non-genetic factors in type 1 diabetes

Type 1 insulin-dependent diabetes is due to destruction of the insulin secreting cells of the islets of Langerhans. The disease is caused by non-genetic, probably environmental, factors operating in a genetically susceptible host to initiate a destructive immune process. These unknown environmental factors may operate over a limited period either in early or later and to a variable degree, playing a particularly substantial role in adults. The environment then induces an immune process associated with destruction of the islet beta cell that can be detected in early life and persists up to disease onset. Apart from an association with the insulin gene there is no evidence that genes associated with type 1 diabetes, including HLA and CTLA4 influence the targeting of the immune response to the insulin-secreting cells. The critical period of immune activation is probably short and the process leading to diabetes probably has a long prodrome but of variable duration that determines the age at presentation with clinical disease. The amplification both of this immune response and the destructive process is in part genetically determined, involving HLA genes. The clinical spectrum of the disease process associated with type 1 diabetes is wide, encompassing insulin-dependence, non-insulin dependence and even transient impaired glucose tolerance. Type 1 diabetes presenting in adults, in contrast to children, is predominantly determined by non-genetic factors with a reduced role for protective and susceptibility HLA alleles. Thus, the evidence is that genes involved in genetic susceptibility to type 1 diabetes operate predominantly in children not adults and in both amplify the immune response and the rate of disease progression.

Disease-associated autoantibodies as predictive markers of type 1 diabetes mellitus in siblings of affected children

The long latent preclinical period of type 1 diabetes mellitus (DM) makes it possible to identify individuals at increased risk for clinical DM before the beta-cell destructive process has reached the point of no return. A series of reports on the predictive value of DM-associated autoantibodies are available in first-degree relatives of patients with type 1 DM, but only a few of these studies target exclusively siblings and young siblings of affected children. When planning screening of siblings for DM risk, their age needs to be considered, as predictive characteristics of autoantibodies seem to vary in different age groups. Autoimmunity may be initiated early in life and therefore early screening for signs of beta-cell autoimmunity is crucial to avoid missing young children en route to overt DM and to be able to start intervention, when clinically applicable preventive modalities become available, before the disease process has advanced too far. Young age, positivity for at least two autoantibodies, high levels of autoantibodies and low first phase insulin response are highly predictive for progression to clinical disease in initially unaffected siblings of children with type 1 DM.

The antiviral 2',5'-oligoadenylate synthetase is persistently activated in type 1 diabetes

Type 1 diabetes results from autoimmune destruction of the pancreatic beta-cells. Although viruses have been implicated as etiologic factors, specific pathogenic mechanisms have not been identified. Recently, increased attention has focused on the role of the innate antiviral defense system in directing adaptive immune responses. In this context, the pathogenesis of type 1 diabetes may involve an aberrant response to endogenous or exogenous viruses or their products. The family of 2',5' oligoadenylate synthetases (2', 5' AS) are IFN-alpha-inducible, RNA-dependent effector molecules in the antiviral defense system. We show that lymphocytic 2',5' AS activity is significantly increased in type 1 diabetes, both in recent-onset and in long-standing type 1 diabetes, and in diabetic twins from monozygotic twin pairs. The activity of 2',5' AS was not elevated in patients with type 2 diabetes or multiple sclerosis thus excluding hyperglycemia or autoimmunity per se as inducing upregulation of enzyme activity. In recent-onset diabetic patients, lymphocyte levels of protein kinase p68 and MxA, two other IFN-alpha-inducible antiviral proteins, were similar to control levels. These data suggest that the increased 2',5' AS activity may reflect an aberrant response to viruses or RNA molecules originating from exogenous or endogenous sources.

Glucose-6-phosphate dehydrogenase deficiency-induced hemolysis in newly diagnosed diabetic monozygotic twins

A pair of monozygotic male twins are described who manifested hemolysis at the concurrent onset of diabetes type 1. Hemolysis appeared progressively following the correction of hyperglycemia and ketoacidosis (one twin). It was found to be related to unknown glucose 6-phosphate dehydrogenase (G-6-PD) deficiency. Other causes of hemolysis such as drugs or bacterial infection were excluded. The fall in glucose availability after the correction of hyperglycemia is proposed as a possible explanation for hemolysis.

Radicals and oxidative stress in diabetes

Recent evidence is reviewed indicating increased oxidative damage in Type 1 and Type 2 diabetes mellitus as well as deficits in antioxidant defence enzymes and vitamins. Mechanisms are considered whereby hyperglycaemia can increase oxidative stress, and change the redox potential of glutathione and whereby reactive oxygen species can cause hyperglycaemia. It is argued that oxygen, antioxidant defences, and cellular redox status should now be regarded as central players in diabetes and the metabolic syndrome.

No association between birth weight and Type 1 diabetes mellitus--a twin-control study

AIMS

To investigate, by means of a twin-control study, whether there is a relationship between birth weight and Type 1 diabetes mellitus.

METHODS

In the youngest part (n = 20 888 pairs) of the Danish Twin Register, 95 twin pairs (26 monozygotic and 69 dizygotic) with Type 1 diabetes were identified. Information about birth weight and birth length, prematurity, maternal age and parity was obtained from midwives' records and from the Danish Medical Birth Registry and analysed using Student's two-sided t-test, Chi-square test and logistic regression.

RESULTS

Birth data were available for 83 diabetic and 51 healthy twin individuals, altogether 67 twin pairs (20 monozygotic and 47 dizygotic). Mean birth weight was 2537 g and 2565 g (NS) in monozygotic and dizygotic pairs and the corresponding length at birth 47.6 cm and 48.2 cm (NS). In pairs discordant for diabetes, the mean birth weight was 2538 g in twins with diabetes and 2549 g in twins without diabetes (NS). Logistic regression in discordant pairs showed no relationship between diabetes status and birth weight, birth length, birth order, sex or prematurity. Logistic regression in concordant vs. discordant pairs showed no effect of mean birth weight and birth length, maternal age, parity or weeks of prematurity.

CONCLUSIONS

There is no association between Type 1 diabetes mellitus and birth weight in this study. Furthermore, variables related to birth weight and length cannot explain why some pairs are concordant while other remain discordant.

Type 1 Diabetes

Type 1 (insulin-dependent) diabetes occurs worldwide and can appear at any age. The genetic susceptibility is strongly associated with HLA-DQ and DR on chromosome 6, but genetic factors on other chromosomes such as the insulin gene on chromosome 11 and the cytotoxic T-lymphocyte antigen gene on chromosome 2 may modulate disease risk. Numerous studies further support the view that environmental factors are important. Gestational infections may contribute to initiation, whereas later infections may accelerate islet β-cell autoimmunity. The pathogenesis is strongly related to autoimmunity against the islet β cells. Markers of autoimmunity include autoantibodies against glutamic acid decarboxylase, insulin, and islet cell antigen-2, a tyrosine phosphatase-like protein. Molecular techniques are used to establish reproducible and precise autoantibody assays, which have been subject to worldwide standardization. The diagnostic sensitivity (40–80%) and specificity (99%) of all three autoantibodies for type 1 diabetes are high, and double or triple positivity among first-degree relatives predicts disease. Combined genetic and antibody testing improved prediction in the general population despite the transient nature of these autoantibodies. Classification of diabetes has also been improved by autoantibody testing and may be used in type 2 diabetes to predict secondary failure and insulin requirement. Islet autoantibodies do not seem to be related to late complications but rather to metabolic control, perhaps because the presence of islet cell autoantibodies marks different residual β-cell function. Combined genetic and autoantibody screening permit rational approaches to identify subjects for secondary and tertiary intervention trials.

Coding of occupation for the ``young cohort'' of the Danish twin register

Objectives: Information on health-related outcomes and exposures is available in user-friendly computerized format for the ``young cohort'' of the Danish Twin Register born 1953-82. We incorporated occupation information within the database to facilitate future job-related studies. Methods: Occupation information for the 29,430 twins responding to a mailed questionnaire in 1995 was coded according to DISCO-88. The subjects were classified in three ways depending on the information available: directly from the 2,196 job titles listed in the DISCO-88 handbook, according to a set of predetermined rules, or by consensus if ambiguous information was provided. Two percent (2%) of the sample was recoded independently by two investigators to demonstrate coding consistency. Results: Occupation could be directly coded using job titles for 61% of the sample; 15% were coded according to a set of rules or by consensus; 24% could not be coded. The recoded sample was 99% in agreement with the original coding. Conclusion: Occupation information has been incorporated within the extensive health-related database for the ``young cohort'' of the Danish Twin Register. This resource is available to researchers for future studies concerning occupation, health, and heredity using (1) the existing data (2) via linkage to other Danish databases, or (3) by contacting selected subjects directly.

Genetic determination of islet cell autoimmunity in monozygotic twin, dizygotic twin, and non-twin siblings of patients with type 1 diabetes: prospective twin study

OBJECTIVE

To test the hypothesis that non-diabetic dizygotic and monozygotic twin siblings of patients with type 1 diabetes have a similar high prevalence of islet cell autoantibodies, thus suggesting that islet cell autoimmunity is mainly environmentally determined.

DESIGN

Prospective twin study.

SETTING

Two specialist centres for diabetes in the United States.

PARTICIPANTS

Non-diabetic monozygotic twin (n=53), dizygotic twin (n=30), and non-twin (n=149) siblings of patients with type 1 diabetes; 101 controls.

MAIN OUTCOME MEASURES

Analysis of progression to diabetes and expression of anti-islet autoantibodies.

RESULTS

Monozygotic twin siblings had a higher risk of progression to diabetes (12/53) than dizygotic twin siblings (0/30; P<0.005). At the last follow up 22 (41.5%) monozygotic twin siblings expressed autoantibodies compared with 6 (20%) dizygotic twin siblings (P<0.05), 16 (10.7%) non-twin siblings (P<0.0001), and 6 (5.9%) controls (P<0.0001). Monozygotic twin siblings expressed multiple (>/=2) antibodies more often than dizygotic twin siblings (10/38 v 1/23; P<0.05). By life table analysis the probability of developing positive autoantibodies was higher among the monozygotic twin siblings bearing the diabetes associated HLA DQ8/DQ2 genotype than in those without this genotype (64.2% (95% confidence interval 32.5% to 96%) v 23.5% (7% to 40%) at 10 years of discordance; P<0.05).

CONCLUSION

Monozygotic and dizygotic twins differ in progression to diabetes and expression of islet cell autoantibodies. Dizygotic twin siblings are similar to non-twin siblings. These two observations suggest that genetic factors play an important part in determination of islet cell autoimmunity, thus rejecting the hypothesis. In addition, there is a high penetrance of islet cell autoimmunity in DQ8/DQ2 monozygotic twin siblings.

New insights into the epidemiology of type 1 diabetes in Mediterranean countries

In Mediterranean countries, the incidence (per 100,000 per year) of Type 1 diabetes in children aged under 15 years shows wide variation from country to country, ranging from 2.45 in Macedonia to 34.4 in Sardinia. By interacting with environmental factors such as diet, toxins or viral infections, the HLA plus non-HLA genes of susceptibility or resistance to Type 1 diabetes so far identified are the strongest determinants of the disease as far as incidence, age at onset and sex ratio are concerned. The distribution of these genes in the Mediterranean region is still not completely known. Sardinians are the most suitable population for studying such phenomena for three main reasons: their genetic features have been repeatedly analysed in depth; their incidence rate of Type 1 diabetes is by far the highest in the Mediterranean area; and considerable colonies of Sardinian emigrants settled in neighbouring low-incidence Italian regions. Studies on Spaniards and Jews have also contributed to a better understanding of the respective roles of genetic and environmental factors. From a body of research on the Mediterranean populations, it can be concluded that great genetic heterogeneity accounts for the wide variation in incidence of Type 1 diabetes, while rather ubiquitious environmental factors trigger the disease in genetically predisposed individuals.

Progression to type 1 diabetes is associated with a change in the immunoglobulin isotype profile of autoantibodies to glutamic acid decarboxylase (GAD65). Childhood Diabetes in Finland Study Group

To investigate whether type 1 diabetes in man is associated with a preferential Th1/Th2 response, and whether autoantibodies to one of the main autoantigens would reflect such a response, we characterized the immunoglobulin isotype profile to the 65-kDa isoform of glutamic acid decarboxylase (GAD65) in siblings to IDDM patients. Samples obtained from affected subjects before and at clinical onset of IDDM, from unaffected individuals at high risk and at low risk and from healthy controls were studied. The immunoglobulin isotype profile in the siblings at low risk reflected a more immature, i.e., IgM and Th2 like, i.e., IgE response compared to the progressors and siblings at high risk, with significantly higher median levels of IgM and IgE. The rank order of anti-GAD65 immunoglobulin isotypes was similar in the siblings before and at clinical onset of IDDM, IgG1 > IgG4 > IgM > IgE > IgA > IgG3 > IgG2, but markedly different in the individuals at low risk, IgG1 > IgM > IgE > IgG4 > IgG3 > IgA > IgG2. Based on these observations, we suggest that progression to clinical onset of IDDM is associated with a maturation and a decrease in the Th2 immune response against GAD65; findings which could have implications for future intervention and prediction strategies.

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (&epsi;4) and decrease (&epsi;2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

Disease-associated autoimmunity and prevention of insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is a chronic autoimmune disease with a subclinical prodromal period characterized by selective destruction of insulin-producing beta cells in the pancreatic islets. This process is assumed to be T-cell mediated, but the emergence of disease-associated autoantibodies into the peripheral circulation is usually the first noticeable sign of beta-cell autoimmunity in human IDDM. Recent observations have suggested that beta-cell autoimmunity may be induced in any individual at any time. There are also data indicating that such autoimmunity may have been initiated prenatally in some individuals. Only a proportion of those with signs of islet cell autoimmunity progress to clinical disease, and harmless beta-cell autoimmunity reflected by positivity for a single autoantibody specificity seems to appear without any relation to genetic IDDM susceptibility. One can hypothesize that in most subjects HLA-conferred protection against IDDM prevents the beta-cell process from progressing to a stage of destructive insulitis that may lead to clinical disease. Environmental factors may trigger initial beta-cell damage and subsequently accelerate the destructive process. Non-HLA genes may also be involved in the regulation of the progression rate. Prospective observations of prediabetic individuals have revealed that IDDM-associated autoantibodies tend to appear sequentially, and that those who progress to clinical disease mount a strong humoral immune response to most known disease-associated antigens. This indicates that the immune response associated with beta-cell destruction is not purely T-helper 1 biased. Antigen-specific immunotherapy may in the future offer effective measures to intervene in preclinical IDDM to prevent end-stage insulitis. Substantially more data have to be generated, however, on the mechanisms, efficacy and safety of such therapy before it is possible to judge its clinical applicability.