Epidemiology of childhood IDDM in Northern Ireland 1989-1994: low incidence in areas with highest population density and most household crowding. Northern Ireland Diabetes Study Group

Secular trends, disease maps and ecological analyses of the incidence of childhood onset Type 1 diabetes in Northern Ireland, 1989-2003

AIMS

To investigate secular trends in the incidence of Type 1 diabetes in Northern Ireland over the period 1989-2003. To highlight geographical variations in the incidence of Type 1 diabetes by producing disease maps and to compare incidence rates by relevant area characteristics.

METHODS

New cases of Type 1 diabetes in children aged 0-14 years in Northern Ireland were prospectively registered from 1989 to 2003. Standardized incidence rates were calculated and secular trends investigated. Bayesian methodology was used to produce maps of disease incidence using small geographical areas (582 electoral wards). Ecological analyses were conducted using Poisson regression to investigate incidence rates by area characteristics at a finer geographical subdivision (5022 census output areas).

RESULTS

In Northern Ireland during 1989-2003, there were 1433 new cases, giving a directly standardized incidence rate of 24.7 per 100,000 person-years. This incidence rate increased by a mean of 4.2% per annum. Disease maps highlighted higher incidence rates in the predominately rural north-east of the province and lower incidence rates in the urban areas around Belfast in the east and Derry in the north-west of the province. Ecological analysis identified higher incidence in rural areas (P < 0.001), areas with low migration rates (P = 0.002), affluent areas (P < 0.0001), sparsely populated areas (P = 0.0001) and remote areas (P = 0.005). CONCLUSIONS In Northern Ireland the incidence of Type 1 diabetes is increasing. The observed higher incidence in rural, affluent, sparsely populated and remote areas may reflect a reduced or delayed exposure to infections in these areas.

Putting the pieces of the puzzle together - a series of hypotheses on the etiology and pathogenesis of type 1 diabetes

This paper presents a series of 10 hypotheses on the etiology of type 1 diabetes. We begin with the hypothesis that wheat gluten is one of the elusive environmental triggers in type 1 diabetes. Habitual consumption of wheat gluten increases the intestinal synthesis of dipeptidyl peptidase IV. This enzyme helps to shape the repertoire of peptides released into the small intestine following the ingestion of wheat gluten by catalyzing the release of X-Pro dipeptides from the N-terminus of the proline-rich glutenins and gliadins in wheat gluten. The release of gluten-derived peptides causes the tight junctions of the small intestine to open through a zonulin-dependent mechanism, which allows these peptides to enter the lamina propria where they get presented as antigens by HLA-DQ, -DR and CD1d molecules. Binding of one or more gluten peptides by CD1d leads to abrogation of oral tolerance, and a marked increase in peripheral immune responses to wheat proteins. Furthermore, it is our contention, that in response to beta cell apoptosis during normal remodeling of the pancreas and CCL19/CCL21 expression within the pancreatic lymph nodes (PLNs), gluten-loaded dendritic cells migrate from the small intestine to the PLNs. These dendritic cells present gluten-derived antigens on the surface of the PLNs, which leads to migration of CD4(-)CD8(-) gammadelta and CD4(-)CD8(+) alphabeta T cells to the pancreas where they mediate Fas and perforin dependent cytotoxicity. We also hypothesize that at least one of the type 1 diabetes associated HLA-DR molecules that bind and present wheat-derived peptide(s) also bind and present an islet cell antigen(s), activating plasma cell synthesis of islet cell autoantibodies and irrevocable, complement-dependent destruction of islet cells. Our final two hypotheses state that type 1 diabetes morbidity is reduced in those areas of globe where genetically susceptible individuals get adequate amounts of vitamin D, in the diet and/or through exposure to sunlight, and in areas where people are exposed to bacterial, viral, or parasitic infections in early childhood.

No evidence for a major effect of two common polymorphisms of the catalase gene in type 1 diabetes susceptibility

BACKGROUND

Type 1 diabetes (T1D) is a multifactorial disease, the genetic analysis of which has yielded few true positive linkage and association results. Replication of association in independent, large-sample studies is essential to further identify the genes involved in T1D. Two single nucleotide polymorphisms (SNPs) in the catalase gene have been reported to be associated with T1D.

METHODS

Major effects of two SNPs, C1167T (rs769217) and C(-262)T (rs1001179), of the catalase gene on T1D susceptibility have been reported previously in Russians from Moscow. We genotyped C1167T and C(-262)T in large family (1642 families) and British case-control (3530 cases and 3930 controls) collections and tested for association with T1D.

RESULTS

We found no evidence of an association between T1D and C1167T or C(-262)T in either the family or case-control collections, or for the D11S2008 microsatellite polymorphism in families. However, we did find limited statistical evidence of an association at C1167T in USA families (P = 0.033; RR for 1167C = 1.23, 95% CI = 1.02-1.49) and C(-262)T in UK families (P = 0.046; RR for (-262)C = 0.86, 95% CI = 0.75-0.99).

CONCLUSION

We found no evidence for a major effect of C1167T or C(-262)T on T1D susceptibility in two large sample collections. Limited statistical evidence of an association at C1167T in USA families and C(-262)T in UK families was found, but these results are likely to be false positives. The previously reported association of these SNPs may also have been a false positive, or a population specific association in Russians from Moscow.

Higher incidence of childhood-onset type 1 diabetes mellitus in remote areas: a UK regional small-area analysis

AIMS/HYPOTHESIS

We investigated the association between the incidence of type 1 diabetes mellitus and remoteness (a proxy measure for exposure to infections) using recently developed techniques for statistical analysis of small-area data.

SUBJECTS, MATERIALS AND METHODS

New cases in children aged 0 to 14 years in Northern Ireland were prospectively registered from 1989 to 2003. Ecological analysis was conducted using small geographical units (582 electoral wards) and area characteristics including remoteness, deprivation and child population density. Analysis was conducted using Poisson regression models and Bayesian hierarchical models to allow for spatially correlated risks that were potentially caused by unmeasured explanatory variables.

RESULTS

In Northern Ireland between 1989 and 2003, there were 1,433 new cases of type 1 diabetes, giving a directly standardised incidence rate of 24.7 per 100,000 person-years. Areas in the most remote fifth of all areas had a significantly (p=0.0006) higher incidence of type 1 diabetes mellitus (incidence rate ratio=1.27 [95% CI 1.07, 1.50]) than those in the most accessible fifth of all areas. There was also a higher incidence rate in areas that were less deprived (p<0.0001) and less densely populated (p=0.002). After adjustment for deprivation and additional adjustment for child population density the association between diabetes and remoteness remained significant (p=0.01 and p=0.03, respectively).

CONCLUSIONS/INTERPRETATION

In Northern Ireland, there is evidence that remote areas experience higher rates of type 1 diabetes mellitus. This could reflect a reduced or delayed exposure to infections, particularly early in life, in these areas.

Space-time clustering analyses of type 1 diabetes among 0- to 29-year-olds in Yorkshire, UK

AIMS/HYPOTHESIS

Infections have been suggested to play a role in the aetiology of type 1 diabetes. The presence of space-time clustering is consistent with the notion of an environmental component in disease aetiology, possibly linked to infections. We tested for evidence of space-time clustering among children and young adults under 30 years of age using data from a population-based register in Yorkshire, UK.

SUBJECTS AND METHODS

Two data sets of children and young people diagnosed with type 1 diabetes were analysed: (1) children aged 0-14 years and resident in Yorkshire during 1978-2002; (2) those aged 15-29 years and resident in West Yorkshire during 1991-2002. Tests for space-time interactions between cases were applied. Addresses at diagnosis were geo-coded and used as the basis for the analyses.

RESULTS

The study analysed 3,019 type 1 diabetic patients in the 0-14 years age group and 989 patients in the 15-29 years group. Statistically significant space-time clustering based on place and time of diagnosis was detected both for the 10-14-year-olds (p=0.04) and for the 15-19-year-olds (p=0.01).

CONCLUSIONS/INTERPRETATION

Previous studies of clustering of type 1 diabetes have generally been restricted to childhood. Our results from a data set that includes teenagers and young adults show that space-time clustering was limited to young people aged 10-19 years. This finding is consistent with an aetiology involving late exposure to infection. However, the question of whether this is directly diabetogenic or unmasks latent diabetes cannot be addressed by this methodology.

Analysis of polymorphisms in 16 genes in type 1 diabetes that have been associated with other immune-mediated diseases

Background

The identification of the HLA class II, insulin (INS), CTLA-4 and PTPN22 genes as determinants of type 1 diabetes (T1D) susceptibility indicates that fine tuning of the immune system is centrally involved in disease development. Some genes have been shown to affect several immune-mediated diseases. Therefore, we tested the hypothesis that alleles of susceptibility genes previously associated with other immune-mediated diseases might perturb immune homeostasis, and hence also associate with predisposition to T1D.

Methods

We resequenced and genotyped tag single nucleotide polymorphisms (SNPs) from two genes, CRP and FCER1B, and genotyped 27 disease-associated polymorphisms from thirteen gene regions, namely FCRL3, CFH, SLC9A3R1, PADI4, RUNX1, SPINK5, IL1RN, IL1RA, CARD15, IBD5-locus (including SLC22A4), LAG3, ADAM33 and NFKB1. These genes have been associated previously with susceptibility to a range of immune-mediated diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Graves' disease (GD), psoriasis, psoriatic arthritis (PA), atopy, asthma, Crohn disease and multiple sclerosis (MS). Our T1D collections are divided into three sample subsets, consisting of set 1 families (up to 754 families), set 2 families (up to 743 families), and a case-control collection (ranging from 1,500 to 4,400 cases and 1,500 to 4,600 controls). Each SNP was genotyped in one or more of these subsets. Our study typically had approximately 80% statistical power for a minor allele frequency (MAF) >5% and odds ratios (OR) of 1.5 with the type 1 error rate, α = 0.05.

Results

We found no evidence of association with T1D at most of the loci studied 0.02 <P < 1.0. Only a SNP in ADAM33, rs2787094, was any evidence of association obtained, P = 0.0004 in set 1 families (relative risk (RR) = 0.78), but further support was not observed in the 4,326 cases and 4,610 controls, P = 0.57 (OR = 1.02).

Conclusion

Polymorphisms in a variety of genes previously associated with immune-mediated disease susceptibility and/or having effects on gene function and the immune system, are unlikely to be affecting T1D susceptibility in a major way, even though some of the genes tested encode proteins of immune pathways that are believed to be central to the development of T1D. We cannot, however, rule out effect sizes smaller than OR 1.5.

Absence of breast-feeding is associated with the risk of type 1 diabetes: a case-control study in a population with rapidly increasing incidence

There are indications that the effect of environmental factors on the risk of type 1 diabetes mellitus (T1DM) is increasing over time. This can be documented by the rapid increase of T1DM incidence in genetically stable populations. Our aim was to study an association of T1DM with the variable factors of the perinatal period and of early infancy, using data from children born over a period of changing exposure to some of the studied factors. A case-control dataset was analysed, consisting of 868 diabetic children and 1,466 anonymous controls, mostly schoolmates of the children with T1DM. The data were collected using structured questionnaires completed by parents. After performing univariate analyses, the associations were analysed using multiple logistic regression adjusted for potential confounders, including the year of birth. The risk of T1DM decreased with increasing duration of breast-feeding, while no breast-feeding was associated with an increased T1DM risk, OR=1.93 [95% CI: 1.33-2.80], breast-feeding for more than 12 months was protective, OR=0.42 [95% CI: 0.22-0.81], both being relative to the reference category of breast-feeding for 1-3 months. A short duration of day-care attendance (none or less than 1 year) was weakly associated with the risk of T1DM, OR=1.65 [95% CI: 1.05-2.62]. No association was detected between T1DM and signs of prenatal infections, perinatal stress factors, birth size and weight, indicators of crowding or the presence of a domestic pet in the household. Short breast-feeding period and short attendance to day care is associated with the risk of T1DM in Czech children.

Infections and autoimmune diseases

The high percentage of disease-discordant pairs of monozygotic twins demonstrates the central role of environmental factors in the etiology of autoimmune diseases. Efforts were first focussed on the search for triggering factors. The study of animal models has clearly shown that infections may trigger autoimmune diseases, as in the case of Coxsackie B4 virus in type I diabetes and the encephalomyocarditis virus in autoimmune myositis, two models in which viruses are thought to act by increasing immunogenicity of autoantigens secondary to local inflammation. The induction of a Guillain-Barré syndrome in rabbits after immunization with a peptide derived from Campylobacter jejuni is explained by mimicry between C. jejuni antigens and peripheral nerve axonal antigens. Other models involve chemical modification of autoantigens, as in the case of iodine-induced autoimmune thyroiditis. These mechanisms have so far only limited clinical counterparts (rheumatic fever, Guillain-Barré syndrome and drug-induced lupus or myasthenia gravis) but one may assume that unknown viruses may be at the origin of a number of chronic autoimmune diseases, such as type I diabetes and multiple sclerosis) as illustrated by the convergent data incriminating IFN-alpha in the pathophysiology of type I diabetes and systemic lupus erythematosus. Perhaps the difficulties met in identifying the etiologic viruses are due to the long lag time between the initial causal infection and onset of clinical disease. More surprisingly, infections may also protect from autoimmune diseases. Western countries are being confronted with a disturbing increase in the incidence of most immune disorders, including autoimmune and allergic diseases, inflammatory bowel diseases, and some lymphocyte malignancies. Converging epidemiological evidence indicates that this increase is linked to improvement of the socio-economic level of these countries, posing the question of the causal relationship and more precisely the nature of the link. Epidemiological and clinical data support the hygiene hypothesis according to which the decrease of infections observed over the last three decades is the main cause of the incessant increase in immune disorders. The hypothesis does not exclude an etiological role for specific pathogens in a given immune disorder as might notably be the case in inflammatory bowel diseases. Even in this setting, infections could still have a non-specific protective role. Independently of the need for confirmation by epidemiological prospective studies, the hygiene hypothesis still poses numerous questions concerning the nature of protective infectious agents, the timing of their involvement with regard to the natural history of immune diseases and, most importantly, the mechanisms of protection. Four orders of mechanisms are being explored. Antigenic competition is the first hypothesis (immune responses against pathogens compete with autoimmune and allergic responses). This is probably an important mechanism but its modalities are still elusive in spite of considerable experimental data. Its discussion in the context of homeostatic regulation of lymphocyte pools has shed new light on this hypothesis with possible competition for self MHC peptide recognition and interleukin-7. Another hypothesis deals with immunoregulation. Infectious agents stimulate a large variety of regulatory cells (Th2, CD25+, Tr1, NKT, ...) whose effects extend to other specificities than those which triggered their differentiation (bystander suppression). Infectious agents may also intervene through components which are not recognized as antigens but bind to specific receptors on cells of the immune system. Major attention has recently been drawn to Toll receptors (expressed on macrophages and possibly on regulatory T cells) and TIM proteins present on Th cells, which may express the function of the virus receptor (as in the case of the Hepatitis A virus and Tim-1). Experimental data will be presented to support each of these hypotheses. In any event, the final proof of principle will be derived from therapeutic trials where the immune disorders in question will be prevented or better cured by products derived from protective infectious agents. Numerous experimental data are already available in several models. Preliminary results have also been reported in atopic dermatitis using bacterial extracts and probiotics.

Relationship between the incidence of type 1 diabetes and maternal enterovirus antibodies: time trends and geographical variation

AIMS/HYPOTHESIS

We have previously observed an inverse correlation between the incidence of type 1 diabetes and enterovirus infections in the background population. The aim of this study was to analyse whether maternal enterovirus antibody status, which reflects both the frequency of enterovirus infections and the protection conferred by the mother on the offspring, also correlates with the incidence of type 1 diabetes.

METHODS

Maternal enterovirus antibodies were analysed from serum samples taken from pregnant women between 1983 and 2001 in Finland and Sweden using enzyme immunoassay and neutralisation assays. Comparable samples were also taken between 1999 and 2001 in countries with a lower incidence of diabetes (Estonia, Germany, Hungary, Israel, Lithuania, Russia).

RESULTS

A clear decrease was observed in maternal enterovirus antibody levels over the past 20 years (p<0.0001). The frequency of enterovirus antibodies was higher in countries with a low or intermediate incidence of type 1 diabetes compared with high-incidence countries (p<0.0001).

CONCLUSIONS/INTERPRETATION

These findings are in line with our previous observations supporting the hypothesis that a low frequency of enterovirus infection in the background population increases the susceptibility of young children to the diabetogenic effect of enteroviruses.

Detecting small-area similarities in the epidemiology of childhood acute lymphoblastic leukemia and diabetes mellitus, type 1: a Bayesian approach

Childhood acute lymphoblastic leukemia and diabetes mellitus, type 1, have common epidemiologic and etiologic features, including correlated international incidence and associations with infections. The authors examined whether the diseases' similar large-scale distributions are reflected in small geographic areas while also examining the influence of sociodemographic characteristics. Details of 299 children (0-14 years) with acute lymphoblastic leukemia and 1,551 children with diabetes diagnosed between 1986 and 1998 were extracted from two registers in Yorkshire, United Kingdom. Standardized incidence ratios across 532 electoral wards were compared using Poisson regression, confirming significant associations between population mixing and the geographic heterogeneity of both conditions. Bayesian methods analysis of spatial correlation between diseases by modeling a bivariate outcome based on their standardized incidence ratios was applied; spatial and heterogeneity components were included within a hierarchical random effects model. A positive correlation between diseases of 0.33 (95% credible interval: -0.20, 0.74) was observed, and this was reduced after control for population mixing (r = 0.18), population density (r = 0.14), and deprivation (r = 0.06). The Bayesian approach showed a modest but nonsignificant joint spatial correlation between diseases, only partially suggesting that the risk of both was associated within some electoral wards. With Bayesian methodology, population mixing remained significantly associated with both diseases. The links between diabetes and acute lymphoblastic leukemia observed for large regions are weaker for small areas. More powerful replications are needed for confirmation of these findings.

A Full Flora, but not Monocolonization by Escherichia coli or Lactobacilli, Supports Tolerogenic Processing of a Fed Antigen

Fed protein undergoes processing and coupling to major histocompatibility complex (MHC) II molecules during passage through the intestinal epithelium, generating a tolerogenic form of the antigen in serum. Transfer of this factor to naïve animals induces tolerance in the recipient. In this study, we investigate what impact colonization with Gram-positive (Lactobacillus plantarum) or Gram-negative (Escherichia coli) bacteria has on tolerogenic processing in the gut. Germ-free (GF), monocolonized or conventional mice were fed ovalbumin (OVA), and their serum was collected and transferred to naïve conventional recipients that were tested for delayed-type hypersensitivity against OVA after parenteral immunization. A transferable tolerogenic factor was produced by conventional mice, but not by mice that were germ free or monocolonized with either E. coli or L. plantarum. Conventional, but neither GF nor monocolonized mice showed upregulation of MHCII expression in the epithelium of small intestine. The results suggest that a complex intestinal microflora is needed to support oral tolerance development.

Diabetes care provision and glycaemic control in Northern Ireland: a UK regional audit

AIMS

To assess the care received, compared to national guidelines, and to investigate factors associated with glycaemic control in children and adolescents with type 1 diabetes attending clinics in Northern Ireland.

METHODS

An audit of the care provided to all patients attending 11 paediatric diabetes clinics commenced in 2002. A research nurse interviewed 914 patients completing a questionnaire recording characteristics, social circumstances, and aspects of diabetes management, including the monitoring of complications and access to members of the diabetes team. Glycaemic control was measured by glycosylated haemoglobin (HbA1c), determined at a DCCT aligned central laboratory.

RESULTS

The average HbA1c concentration was 8.8% (SD 1.5%), with 20% of patients achieving recommended HbA1c levels of less than 7.5%. In the year prior to the audit, 76% of patients were reviewed by a diabetes specialist nurse and 42% were tested for microalbuminuria. After adjustment for confounding factors, better glycaemic control was identified, particularly in patients who had attended exactly four diabetes clinics in the previous year, were members of the patient association Diabetes UK, and lived with both natural parents.

CONCLUSIONS

In Northern Ireland only a minority of patients achieved recommended HbA1c levels. Furthermore, children and adolescents with diabetes were reviewed by fewer specialists and were less intensively monitored for microvascular complications than recommended. There was evidence of better control in children who were members of Diabetes UK, suggesting that parental attitude and involvement could lead to benefits.

Interleukin 18 promoter polymorphisms are not strongly associated with type I diabetes in a UK population

Interleukin 18 (IL18) is a proinflammatory cytokine whose levels are increased in the subclinical stage of insulin-dependent (type I) diabetes mellitus. Previous case-control studies have reported associations between IL18 -607C>A and -137G>C promoter polymorphisms and type I diabetes. We performed case-control and family-based association studies employing Pyrosequencing to assess if these IL18 polymorphisms are also associated with the development of type I diabetes in the Northern Ireland population. The chi2 analysis of genotype and allele frequencies for the IL18 polymorphisms in cases (n=433) vs controls (n=426) revealed no significant differences (P>0.05). Assessment of allele transmission distortion from informative parents to affected offspring also failed to confirm previously reported associations. Stratification of these analyses for age-at-onset and HLA-DR type did not reveal any significance associations. In conclusion, our data do not support the strong positive associations of IL18 promoter polymorphisms with type I diabetes reported in previous smaller studies.

Younger age at diagnosis of type 1 diabetes mellitus in children of immigrated families born in Italy

The aim of this study was to evaluate the age of immigrants' children at diagnosis of Type 1 diabetes (T1DM) according to their country of birth. Immigration from developing countries to a westernised area causes rapid changes in the environmental conditions, and we investigated whether the location of birth, either inside or outside Italy, is associated with age at diagnosis of diabetes. Out of a prevalent hospital-based cohort of 5718 T1DM children cared for in 2002 in 47 Italian Pediatric Diabetes Units, we recruited 195 children (M: 97) of immigrants from developing countries--119 were born in Italy and 76 outside the European Union. Children with only one immigrant parent (no. 42) were also included. Age at diagnosis of T1DM, and other variables were compared with those of Italian children. Children of immigrated families born in Italy developed T1DM at a median age of 4.0 yr (IQR 2.2-6.9), whereas those born in developing countries and that had immigrated to Italy after birth developed T1DM at a median age of 7.9 yr (IQR 5.1-10.7, p < 0.001). Among the children born in Italy, 77 had parents who were both immigrants and the children's median age at diagnosis was 3.8 yr (IQR 2.1-6.3); 42 had only one immigrant parent and, when it was the father (no. = 23), median age was even younger (2.9 yr, IQR 2.0-8.2). Ten children had immigrated in their first yr of life and their median age was 9.1 yr (IQR 5.0-10.6). The median age of the Italian children was 6.6 yr (IQR 3.6-9.5). Results show that the outbreak of T1DM is earlier in immigrants' children born in Italy than in original countries.

Replication of an association between the lymphoid tyrosine phosphatase locus (LYP/PTPN22) with type 1 diabetes, and evidence for its role as a general autoimmunity locus

In the genetic analysis of common, multifactorial diseases, such as type 1 diabetes, true positive irrefutable linkage and association results have been rare to date. Recently, it has been reported that a single nucleotide polymorphism (SNP), 1858C>T, in the gene PTPN22, encoding Arg620Trp in the lymphoid protein tyrosine phosphatase (LYP), which has been shown to be a negative regulator of T-cell activation, is associated with an increased risk of type 1 diabetes. Here, we have replicated these findings in 1,388 type 1 diabetic families and in a collection of 1,599 case and 1,718 control subjects, confirming the association of the PTPN22 locus with type 1 diabetes (family-based relative risk (RR) 1.67 [95% CI 1.46-1.91], and case-control odds ratio (OR) 1.78 [95% CI 1.54-2.06]; overall P = 6.02 x 10(-27)). We also report evidence for an association of Trp(620) with another autoimmune disorder, Graves' disease, in 1,734 case and control subjects (P = 6.24 x 10(-4); OR 1.43 [95% CI 1.17-1.76]). Taken together, these results indicate a more general association of the PTPN22 locus with autoimmune disease.

Schistosoma mansoni infection modulates the immune response against allergic and auto-immune diseases

Chronic Schistosoma mansoni infection leads to a type 2-immune response with increased production of interleukin (IL-10). Evidence indicates chronic exposure to S. mansoni down regulates the type 1 immune response and prevents the onset of Th1-mediated diseases such as multiple sclerosis, diabetes mellitus and Crohn's disease. Furthermore, our own studies have revealed that chronic exposure to S. mansoni also down regulates atopic disease, Th2-mediated diseases. Our studies show an inverse association between the skin prick test reactivity and infection with S. mansoni and show the severity of asthma is reduced in subjects living in an endemic area of S. mansoni. Moreover, we hypothesize the mechanisms involved in the modulation of inflammatory response in atopic individuals, is likely dependent on IL-10 production, an anti-inflammatory cytokine elevated during helminth infections. Patients with asthma and helminth infections produced less IL-5 than patients with asthma without helminth infections, and this down regulation could, in part, be mediated by IL-10. In conclusion, helminthic infections, through induction of regulatory mechanisms, such as IL-10 production, are able to modulate the inflammatory immune response involved in the pathology of auto-immune and allergic disease.

Household crowding index: a correlate of socioeconomic status and inter-pregnancy spacing in an urban setting

OBJECTIVES

This paper examines the effect of household crowding on inter-pregnancy spacing and its association with socioeconomic indicators, among parous mothers delivered in an urban environment.

DESIGN

Cross sectional survey.

METHODS

Sociodemographic data were obtained on 2466 parous women delivering at eight hospitals in Greater Beirut over a one year period. Statistical methodology comprised Pearson chi(2) test and logistic regression analysis.

MAIN RESULTS

A significant inverse relation was observed between household crowding and socioeconomic status, defined as education and occupation of women and their spouses. Inter-pregnancy spacing increased with higher levels of crowding. Further analysis suggested that this positive association was confounded by maternal demographic characteristics.

CONCLUSIONS

These data have shown that household crowding, a correlate of low parental socioeconomic status, is associated with longer birth intervals. This association, however, seems to be largely explained by maternal age and parity.

Association analysis of the lymphocyte-specific protein tyrosine kinase (LCK) gene in type 1 diabetes

Prior data associating the expression of lymphocyte-specific protein tyrosine kinase (LCK) with type 1 diabetes, its critical function in lymphocytes, and the linkage of the region to diabetes in the nonobese diabetic (NOD) mouse model make LCK a premier candidate for a susceptibility gene. Resequencing of LCK in 32 individuals detected seven single nucleotide polymorphisms (SNPs) with allele frequencies >3%, including four common SNPs previously reported. These and six other SNPs from dbSNP were genotyped in a two-stage strategy using 2,430 families and were all shown not to be significantly associated with type 1 diabetes. We conclude that a major role for the common LCK polymorphisms in type 1 diabetes is unlikely. However, we cannot rule out the possibility of there being a causal variant outside the exonic, intronic, and untranslated regions studied.

Type 1 diabetes mellitus in childhood: a matched case control study in Lancashire and Cumbria, UK

AIMS

The aim of the study was to identify environmental risk factors for insulin-dependent diabetes mellitus (Type 1 DM) in childhood.

METHODS

A matched case-control study of Type 1 DM conducted in Lancashire and Cumbria, UK, using a structured interview. Cases (n=196, participation rate 83%) were children under 16 years of age diagnosed prior to October 1998 and attending diabetic clinics. Controls (n=381) were healthy children from the community matched by gender and by age (within a few days of birth). The data were analysed by logistic regression using the technique of Breslow and Day for matched case control studies.

RESULTS

The multivariate regression model showed that the following factors were significantly associated with the risk of developing Type 1 DM (odds ratio, 95% confidence intervals): sharing a room with a sibling (0.458, 0.290-0.721), social contact with other children when aged 6-11 months (0.439, 0.256-0.752), consumption of sugary food (0.080, 0.024-0.261), parental insulin dependent diabetes mellitus (10.651, 3.086-36.761), maternal thyroid disease (4.861, 1.681-14.058), consuming more than one pint of milk per day prior to school entry (0.498, 0.310-0.802), maternal smoking during pregnancy (0.373, 0.218-0.636), a father with no academic qualifications (0.504, 0.278-0.913), maternal age at time of birth (0.900, 0.854-0.948), maternal infections in pregnancy (2.453, 1.011-5.948), other maternal illnesses or conditions in pregnancy (2.007, 1.139-3.535), belonging to an Asian family (0.104, 0.028-0.394), and regular contact with pets and other animals (0.552, 0.309-0.987).

CONCLUSION

Many of the results are consistent with the hygiene hypothesis which links improved living standards with decreased exposure to microorganisms and increased risk of immune mediated disease in childhood. These findings challenge the idea that improved hygiene acts exclusively through a Th2 mechanism leading to atopic disease as Type 1 DM is mediated by a Th1 reaction. The association with maternal smoking could be due to recall bias but a causal link cannot be excluded with confidence.

Geographical mapping of type 1 diabetes in children and adolescents in south east Sweden

STUDY OBJECTIVE

As earlier studies have shown space-time clusters at onset of type 1 diabetes in the south east region of Sweden we investigated if there also has been any geographical clusters of diabetes in this region.

DESIGN

The place of residence (coordinates) at the time of diagnosis were geocoded in a geographical information system (GIS). All children diagnosed with type 1 diabetes up to 16 years of age at diagnosis between 1977-1995 were included. The population at risk was obtained directly from the population registry for the respective years and geographical area levels.

SETTING

South east region of Sweden containing 5 counties, 49 municipalities, and 525 parishes.

MAIN RESULTS

A significant geographical variation in incidence rate were found between the municipalities (p<0.001) but not between the counties. The variation became somewhat weaker when excluding the six largest municipalities (p<0.02). In municipalities with increased risk (>35.1/100 000) the major contribution comes from children in age group 6-10 years of age at diagnosis. There were no obvious differences between the age groups in municipalities with decreased risk (<20.1/100 000). Boys and girls had about the same degree of geographical variation.

CONCLUSIONS

Apart from chance, the most probable explanation for the geographical variation in the risk for children and adolescents to develop type 1 diabetes between the municipalities in the region is that local environmental factors play a part in the process leading to the disease.

Nationwide, prospective registration of type 1 diabetes in children aged <15 years in norway 1989-1998: no increase but significant regional variation in incidence

OBJECTIVE

An increasing incidence rate of childhood-onset type 1 diabetes has been described in several countries, particularly among the youngest children, and the Nordic countries have consistently been shown to have the highest incidence rates. An increasing incidence had previously been reported in Norway for 1973-1982, together with regional variation within the country. The aim of this study was to test whether there has been an increasing incidence of type 1 diabetes and a continued regional variation among children aged <15 years in Norway during 1989-1998.

RESEARCH DESIGN AND METHODS

As a part of the activities of the National Childhood Diabetes Registry of Norway and the EURODIAB study, a 10-year prospective, nationwide case registration of type 1 diabetes was done among children aged <15 years.

RESULTS

A total of 1867 new case subjects (1009 boys and 858 girls) were identified. The total incidence rate was 22.4 per 100000 person-years (95% CI 21.5-23.5). The incidence was 13.1, 26.3, and 28.8 per 100000 in the age-groups 0-4.9, 5-9.9, and 10-14.9 years, respectively. No increase or decrease over time was detected in any of the age-groups during the 10-year period. We found significant variation between the 19 counties, which only partly reflected the pattern previously described for 1973-1982.

CONCLUSIONS

We found a significant regional variation within Norway. After a previous period of increase, the incidence has been stable in all age-groups <15 years during 1989-1998.

Analysis of the type 2 diabetes-associated single nucleotide polymorphisms in the genes IRS1, KCNJ11, and PPARG2 in type 1 diabetes

It has been proposed that type 1 and 2 diabetes might share common pathophysiological pathways and, to some extent, genetic background. However, to date there has been no convincing data to establish a molecular genetic link between them. We have genotyped three single nucleotide polymorphisms associated with type 2 diabetes in a large type 1 diabetic family collection of European descent: Gly972Arg in the insulin receptor substrate 1 (IRS1) gene, Glu23Lys in the potassium inwardly-rectifying channel gene (KCNJ11), and Pro12Ala in the peroxisome proliferative-activated receptor gamma2 gene (PPARG2). We were unable to confirm a recently published association of the IRS1 Gly972Arg variant with type 1 diabetes. Moreover, KCNJ11 Glu23Lys showed no association with type 1 diabetes (P > 0.05). However, the PPARG2 Pro12Ala variant showed evidence of association (RR 1.15, 95% CI 1.04-1.28, P = 0.008). Additional studies need to be conducted to confirm this result.

The belgrade childhood diabetes study: association of infections and vaccinations on diabetes in childhood

PURPOSE

The aim of this study was to investigate whether individual infections or combination of infections or vaccination affect the risk of developing diabetes in childhood.

METHODS

A case-control study was conducted in Belgrade during the period between 1994 and 1997. A total of 105 recent onset diabetics were compared with 210 controls chosen among children with skin disease (the first control group). Cases and controls were individually matched by age (+/-1 year), sex, and place of residence. Eighty-six diabetic children were also compared with their brothers/sisters (the second control group).

RESULTS

After adjustment for confounding variables, independent association with diabetes was found for infections during the 6 months preceding the onset of the disease, when cases were compared with both the first control group (OR=4.23, 95% CI, 1.95-9.17, p<0.001) and the second control group (OR=4.68, 95% CI, 2.09-10.47, p<0.001), and for regular vaccination when cases were compared with the first control group (OR=0.08, 95% CI, 0.01-0.50, p=0.03).

CONCLUSION

The results obtained support the hypotheses that infections play a role in the development of type 1 diabetes and that regular vaccination has a preventive effect.

The incidence of type 1 diabetes among children in Finland—rural–urban difference

The aim of the study was to investigate the incidence of type 1 diabetes among children aged 14 years or under according to the level of urbanization of the place of residence of children at the time of diagnosis in Finland during 1987 to 1996. The analysis was carried out using a Bayesian approach and GIS. The incidence was the highest in the rural heartland areas while the increase in incidence was sharpest in urban areas. The level of urbanization seems to explain only a part of the spatial variation in the incidence in Finland. It is possible that some environmental risk factors for type 1 diabetes have been more prevalent in rural heartland areas than in the rest of the country. These factors might have increased in urban environments in Finland particularly during the first half of 1990s.

Space-time clustering at birth and at diagnosis of type 1 diabetes mellitus in relation to early clinical manifestation

OBJECTIVE

To investigate whether space-time clustering at diagnosis of type 1 diabetes mellitus (DM1) is related to clinical manifestations and to see whether there is a time-space clustering at birth of children who later develop DM1.

PATIENTS

Using the method by Knox, clustering was analysed in all 1,144 children diagnosed between 1977 and 1994 in south-east Sweden.

RESULTS

The strongest significance was obtained for the cut-off value of 5 km and 7 months (p<0.01). Using this cut-off, children with a short duration of symptoms before diagnosis had the same degree of clustering as children with a longer duration. Children diagnosed during autumn and winter tended to have a higher degree of clustering than children diagnosed during spring and summer. We found no significant clustering regarding birthplace and birth month.

CONCLUSION

This study is consistent with the existence of space-time clustering at diagnosis. The most plausible explanation is that infections elicit several cases of DM1 in children in whom the disease process has already begun.

Association of the T-cell regulatory gene CTLA4 with susceptibility to autoimmune disease

Genes and mechanisms involved in common complex diseases, such as the autoimmune disorders that affect approximately 5% of the population, remain obscure. Here we identify polymorphisms of the cytotoxic T lymphocyte antigen 4 gene (CTLA4)--which encodes a vital negative regulatory molecule of the immune system--as candidates for primary determinants of risk of the common autoimmune disorders Graves' disease, autoimmune hypothyroidism and type 1 diabetes. In humans, disease susceptibility was mapped to a non-coding 6.1 kb 3' region of CTLA4, the common allelic variation of which was correlated with lower messenger RNA levels of the soluble alternative splice form of CTLA4. In the mouse model of type 1 diabetes, susceptibility was also associated with variation in CTLA-4 gene splicing with reduced production of a splice form encoding a molecule lacking the CD80/CD86 ligand-binding domain. Genetic mapping of variants conferring a small disease risk can identify pathways in complex disorders, as exemplified by our discovery of inherited, quantitative alterations of CTLA4 contributing to autoimmune tissue destruction.

Small area variation in childhood diabetes mellitus in Austria: links to population density, 1989 to 1999

We analyzed the associations of environmental factors with the regional distribution of Type 1 diabetes mellitus in Austria. All newly diagnosed cases (n=1449) from 1989 to 1999 were allocated to districts using the postal code. Nitrate content of the water was measured by the Austrian Federal Environmental Agency. Data on infant mortality, population density, and percentage of employment by industry were derived from Statistics Austria. An inverse effect was seen between the proportion of children younger than 15 years of age and the risk ratio (P<.01). Infant mortality, population density, and percentage of persons with employment in industry were not of significant influence. The mean nitrate level was positively associated (P=.07). In regions with a higher percentage of children younger than 15 years of age, fewer children developed diabetes, which is in agreement with the observation that early social mixing is a protective factor. Nitrate levels may have a confounding effect.

Incidence of type 1 diabetes in Lithuanians aged 0-39 years varies by the urban-rural setting, and the time change differs for men and women during 1991-2000

OBJECTIVE

Type 1 diabetes has been associated with factors related to welfare and social class. During the past decade, Lithuania has experienced a transition period, leading to dramatic changes in the socioeconomic structure of the society.

RESEARCH DESIGN AND METHODS

Incidence in the group aged 0-39 years by urban-rural setting (cities >100000 inhabitants, towns, and rural areas), period (1991-1995 and 1996-2000), age, and sex were studied using Poisson regression.

RESULTS

The age- and sex-standardized incidence per 100000 inhabitants per year was higher in men aged 0-39 years than in women (9.5 and 6.9, respectively, incidence rate ratio [IRR] = 1.39, P < 0.001). Incidence was lower in rural areas than in towns and cities (7.1, 9.0, and 8.8, respectively, P < 0.001). The urban-rural differences in incidence were most marked among children aged 0-9 years. From 1991-1995 to 1996-2000, the overall incidence increased from 8.7 to 10.5 (IRR = 1.22, P = 0.001) in men and from 6.2 to 7.8 (IRR = 1.25, P = 0.002) in women. For men, the increase over time occurred predominantly in the cities, from 8.4 to 11.8 (IRR = 1.40, P < 0.001), and in the older age-groups. In contrast, for women, the incidence increased more in small towns and rural areas, from 5.8 to 7.7 (IRR = 1.33, P = 0.003), and in the younger age-groups.

CONCLUSIONS

The incidence of type 1 diabetes in Lithuania differs depending on the urban-rural setting, and the pattern of change over time differs between the sexes, both by urban-rural setting and age-group. The findings support the theory that lifestyle-related factors connected to socioeconomic status are important for the occurrence of type 1 diabetes.

The IL12B 3' untranslated region DNA polymorphism is not associated with early-onset type 1 diabetes

A recent study employing Australian and UK type 1 diabetes families has demonstrated significant transmission bias to affected offspring of a polymorphism (1188A allele; termed allele 1) in the 3' untranslated region (3'UTR) of the interleukin 12B (IL12B) gene which encodes the IL-12p40 subunit of the pro-inflammatory cytokine IL-12. However, results from replication studies in other populations have been controversial. We performed both case-control (n=120 cases; n=330 controls) and family-based (n=307 families) association studies, using the transmission disequilibrium test, to investigate if allele 1 is associated with early-onset type 1 diabetes in Northern Ireland. No association was observed between allele 1 and type 1 diabetes in either case-control (80.8% vs 80.8%; P=0.98) or family-based (49.7% transmissions; P=0.94) studies. Our results do not support earlier reports of an association between allele 1 in the 3'UTR of the IL12B gene and type 1 diabetes.

Geography of child mortality clustering within African families

After decades of sustained child mortality reductions, infant and early childhood mortality levels in Africa remain high. This can partly be ascribed to the concentration of child mortality within particular families, communities or geographic localities. Strong mortality clustering is indicative of marked social inequality and of an unequal distribution of health and health-related resources and infrastructures. It also signifies a concentration of nutritional and sanitary behaviors harmful to the good health and longevity of children. Finally, it likely points to the existence of particular genetic problems in certain families, or environmental problems within specific communities. Using nationally representative family level data from all sub-regions of Africa, two important findings emerge from this study. First, levels of mortality have generally declined in all countries over time, and as mortality decreases, mortality clustering tends to follow the same trend. Second, bio-demographic covariates have a more important effect on familial mortality clustering risks than socio-economic ones.

Drinking water composition and childhood-onset Type 1 diabetes mellitus in Devon and Cornwall, England

AIMS

Previous studies have reported inconsistent results on the association between some compositions (e.g. nitrate) in domestic water and the risk of childhood-onset Type 1 diabetes mellitus. This study aimed to examine the relationship between nitrate, zinc and magnesium in drinking water and the risk of childhood-onset Type 1 diabetes mellitus.

METHODS

The study covers the Cornwall and the former Plymouth Health Authority Regions in the far south-west of England. Five hundred and seventeen children, aged 0-15 years, diagnosed with Type 1 diabetes mellitus between 1975 and 1996, were identified for inclusion in the study. Domestic water data (nitrate, Zn, Mg, Cu, Al, Ca, Fe and Mn) between 1993 and 1997 were provided by South-west Water Plc, UK, for each of the 40 Water Supply Zones in which the subjects had been resident at the time of diagnosis. The standardized incidence ratio (SIR) of the disease was calculated for each Water Supply Zone using the UK 1991 census population data. The relationship between the SIR of the disease and the water quality indicators in thirds (three strata of low, medium and high concentrations) was examined by chi2 test for trend and Poisson regression analysis.

RESULTS

The initial analyses by chi2 test for trend on the relation of SIRs and drinking water compositions suggested that copper, magnesium and nitrate might have some protective effects, but Poisson regression analyses showed that only zinc and magnesium were significant factors. The data suggest that the incidence rate of childhood diabetes is significantly lower when the concentrations of zinc and magnesium in the domestic drinking water are in the range 22.27-27.00 microg/l (incidence rate ratio (IRR), 0.76; 95% CI, 0.59-0.97) and greater than 2.61 mg/l (IRR, 0.72; 95% CI, 0.58-0.91), respectively.

CONCLUSIONS

Our findings suggest evidence of a possible association between zinc and magnesium in the domestic drinking water and childhood diabetes in the far south-west of England. However, these possible protective effects of zinc and magnesium in domestic drinking water warrant further confirmation.

Possible association between CTLA4 DNA polymorphisms and early onset type 1 diabetes in a UK population

Linkage and association has been reported between CTLA4 DNA markers and susceptibility to type 1 diabetes in some populations, but not others. We performed case-control and family-based association studies to assess if the CTLA4 A49G and intron 1 C/T polymorphisms were associated with development of early onset type 1 diabetes in the Northern Ireland population. The distribution of A49G and C/T alleles in cases (n = 144) was similar to those observed in controls (n = 307). In contrast, significant distortions in allele transmissions from informative parents to probands were observed for both the A49G (P = 0.02) and C/T (P = 0.01) polymorphisms employing 297 nuclear families. Our results suggest that the CTLA4 gene may play a minor role in the overall genetic predisposition to type 1 diabetes in this UK population.

Population mixing and childhood diabetes

BACKGROUND

Exposure to infections, particularly in early life, may modify the risk of developing childhood diabetes. Population mixing, based on the number and diversity of incoming migrants to an area can be used as a proxy measure for exposure to infections. We tested the hypothesis that incidence of childhood Type 1 diabetes is higher in areas of low population mixing.

METHODS

Children (<15 years) diagnosed with diabetes between 1986--1994 in Yorkshire, UK (n = 994) were analysed with demographic data and denominator populations from the 1991 UK Census. Population mixing was estimated separately for 'any age' (>1 year) and children (1--15 years) for each area, using the proportion of migrants and an index of diversity based on numbers and origins of migrants. Regression models calculated the effect of 'any age' and childhood population mixing on the incidence of diabetes, controlling for population density, ethnicity and proportion of migrants.

RESULTS

Areas with low levels of population mixing of children (bottom decile), were significantly associated with higher incidence of childhood diabetes for 0-14 years (incidence rate ratio [IRR] = 1.46, 95% CI : 1.01--2.11). When stratified by age different effects were observed for childhood population mixing with raised IRR for ages 5-9 (2.23, 95% CI : 1.20--4.11) and 10-14 (1.47, 95% CI : 0.89--2.42), and decreased IRR for 0--4-year-olds (0.56, 95% CI : 0.17--1.82).

CONCLUSION

The incidence of childhood diabetes is highest in areas where limited childhood population mixing occurs and the diversity of origins of incoming children is low; those over 4 years are at greatest risk. This is consistent with an infectious hypothesis where absence of stimulation to the developing immune system increases vulnerability to late infectious exposure, which may precipitate diabetes.

Family characteristics and life events before the onset of autoimmune type 1 diabetes in young adults: a nationwide study

OBJECTIVE

To elucidate whether family characteristics and stressful life events were associated with onset of autoimmune type 1 diabetes in young adults.

RESEARCH DESIGN AND METHODS

This investigation was based on a nationwide study (Diabetes Incidence Study in Sweden) of newly diagnosed patients aged 15-34 years. Patients clinically classified as type 1 diabetic with antibodies to islet cells and/or to GAD65 were compared with age- and sex-matched control subjects via questionnaire. The questionnaire covered diabetes heredity, social environment, educational level, and life events experienced during the 12 months before diagnosis.

RESULTS

The rate of response was 82% for the diabetic patients and 65% for the control subjects. Questionnaires from 349 diabetic patients and 979 control subjects were considered. Diabetes in relatives was more frequent in the patients (odds ratio [OR]2.6) who were born in Sweden and whose mothers were of Swedish origin. No major stress factors were detected in the diabetic patients; however, in comparison with the control subjects, the diabetic patients had experienced fewer conflicts with their parents and had less often broken contacts with friends.

CONCLUSIONS

Young adults with recent-onset type 1 diabetes were more exposed to heredity for diabetes, but no major prediabetic stress factors were detected. Our study does not directly support the concept that psychosocial stressful life events are involved in the development of autoimmune type 1 diabetes in young adults.

Protective role of infections and vaccinations on autoimmune diseases

Infectious agents may induce autoimmune disease through several mechanisms, notably antigen mimicry and inflammation of the target organ; conversely, infections may protect from autoimmune diseases. This paradoxical effect has been demonstrated for a number of bacteria, viruses and parasites on a variety of spontaneous or experimentally induced animal models of autoimmune diseases (e.g. experimental allergic encephalomyelitis, lupus mice, non-obese diabetic mice). The mechanisms of the protection are still ill-defined, and probably vary according to models. Stimulation of immunoregulatory CD4 T cells has been shown to play a central role in several major models. The role of superantigens is also important, like that of Toll-like receptors. Antigen competition is another major mechanism, itself open to several interpretations. Epidemiological data support a protective role of infections on human allergic and autoimmune diseases. These diseases are much more common in countries with high socio-economic development (typically Northern countries in Europe). The reason for this cannot be fully explained by genetic differences because migrating populations develop these diseases with the same incidence of the adoptive country rather than that of the country of origin. It is interesting that the frequency of these diseases has been increasing in developed countries over the last 20 years but not in undeveloped ones.

The epidemiology of childhood-onset type 1 diabetes mellitus in Romania. ONROCAD Study Group. National Romanian Organisation for the Care of Diabetic Children and Adolescents

The ONROCAD Study group was established to provide descriptive epidemiological information on type 1 diabetes mellitus (DM) in Romania. Data on all new patients with type 1 DM with onset before age 15 years during the four-year period 1992-1995 in Romania were submitted from all members of the ONROCAD Study Group, representing all doctors and clinics that manage children with DM in Romania. Age- and sex-specific incidence rates were estimated, using available demographic data. A total of 706 new patients with type 1 DM and onset 0-14 years was registered. The overall completeness of ascertainment was estimated at 93.5%. For all Romania, the incidence of childhood-onset type 1 DM was estimated at 3.57/100,000/year. The incidence in the three regions was statistically significantly different (p = 0.002), with high rates in Transylvania and low rates in Muntenia. Girls had a significantly higher incidence than boys for each of the age groups 0-4, 5-9 and 10-14 years. Between these age groups, the incidence increased significantly with age. The incidence of childhood-onset type 1 DM is among the lowest recorded in Europe. Significant, but unexplained, geographical variation exists within Romania. Searches for factors to explain this heterogeneity may provide clues to the etiology of childhood-onset type 1 DM.

Seasonality of birth in children (0-14 years) with type 1 diabetes mellitus in Slovenia

The aim of this study was to find out whether there is seasonality of month of birth of children with diabetes in Slovenia and if so whether it differs from that of the general population. A cohort of 849 children and adolescents (0-14 years) with type 1 diabetes mellitus born between 1956 and 1998 were included in the study. Monthly and seasonal patterns of birth of the patients with diabetes were compared with the pattern of normal live births (n = 1,345,921) and the pattern of disease onset. Statistical analysis was made using Student's t-test to compare the means between the four seasons of the year, and single cosinor analysis for a period of 12 months. The children and adolescents with diabetes had a statistically significant different seasonality of month of birth compared to that of the general population, and an opposite pattern from the seasonality of month of onset of disease. The observations made are in accordance with observations made recently in other countries and support the hypothesis that a virus infection transmitted by the mother to the fetus during the annual viral epidemic induces the autoimmune process in the pancreatic beta-cells in genetically susceptible individuals who will subsequently develop clinical diabetes during childhood.

Month of birth and subsequent development of type I diabetes (IDDM)

The aim of this study was to find out whether there is a seasonal pattern in the month of birth of children with IDDM in Israel and whether this pattern, if present, differs from that of total live births. One thousand and ninety-five out of 1,188 children and adolescents (0-17 years) who developed IDDM in Israel between 1980-1993 and whose month of birth was known were included in the study. Separate analysis was made for Jews (n = 987) who have a high incidence (10-18/105) and Arabs (n = 108) with a low incidence (2.9/105) of IDDM. The pattern of total live birth distribution in Israel over a 20-year period served as control. A significantly different seasonal pattern was found in the two IDDM populations. Whereas the Jews had the lowest number of births in winter (January-March) and the highest in spring (April-June), the Arabs presented an inverse pattern in the first months of the year. The distribution of births of the children who developed IDDM was different from that observed in total live births in the Jewish population. The findings in the Jewish population in Israel (a high incidence group) support the hypothesis that IDDM is triggered in some children by viral infections transmitted by the mother during pregnancy or in the early postnatal period. In the Arab population (a low incidence group) a protective (immune and/or genetic) mechanism may exist.

Viruses and other perinatal exposures as initiating events for beta-cell destruction

There is strong evidence that the aetiology of insulin-dependent diabetes mellitus (IDDM) is due to a complex interaction between genes and the environment and that the pathogenesis is autoimmune. In early perinatal life the immune system is induceable and exposures in this period may initiate autoimmunity. Recent findings of time and space clustering of birth dates for later diabetic cases together with the early observation of a very high prevalence of diabetes in cases with rubella embryopathy suggest that foetal virus exposure may be important. Recent findings from Sweden and Finland suggest that enterovirus exposure during foetal life may initiate autoimmunity which may lead to diabetes. Other immune events, such as maternal-foetal blood group incompatibility and pre-eclampsia in the mother have also been associated with IDDM risk. Other more unspecific events in the perinatal period, such as a short gestational age, caesarean section and neonatal respiratory disease, are also indicated to increase the risk. In addition, food components such as nitrosamine components, cow's milk protein and gliadin have been proposed to initiate the slowly progressing autoimmune beta-cell destruction. Most of these epidemiological findings are supported by experimental studies in the nonobese diabetic mice but their exact mechanisms of action are still unclear. It is concluded that new evidence is accumulating indicating that perinatal exposures may be important for the initiation of beta-cell destruction. As such risk factors may be targets for primary prevention strategies further studies are urgently warranted.