Molecular IDDM epidemiology: international studies. WHO DiaMond Molecular Epidemiology Sub-Project Group

The geoepidemiology of type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by absolute insulin deficiency resulting from the progressive immune-mediated destruction of pancreatic islet beta cells. It is thought to be triggered by as yet unidentified environmental factors in genetically susceptible individuals, the major genetic contribution coming from loci within the HLA complex, in particular HLA class II. The worldwide incidence of T1D varies by at least 100-fold, being highest in Finland and Sardinia (Italy) and lowest in Venezuela and China. The incidence has been increasing worldwide at an annual rate of approximately 3%. While genetic factors are thought to explain some of the geographic variability in T1D occurrence, they cannot account for its rapidly increasing frequency. Instead, the declining proportion of newly diagnosed children with high-risk genotypes suggests that environmental pressures are now able to trigger T1D in genotypes that previously would not have developed the disease during childhood. Although comparisons between countries and regions with low and high-incidence rates have suggested that higher socioeconomic status and degree of urbanization are among the environmental factors that play a role in the rising incidence of T1D, the findings are too inconsistent to allow firm conclusions. Morbidity and mortality as well as causes of death also show considerable geographic variation. While glycemic control has been identified as a major predictor of the micro- and macrovascular complications of T1D and shows considerable geographical variability, it does not appear to be the only factor involved in the regional differences in complication rates. The role of genetics in susceptibility to nephropathy, retinopathy and other diabetic complications largely remains to be explored.

Perinatal risk factors for childhood Type 1 diabetes in Western Australia--a population-based study (1980-2002)

AIMS

To investigate perinatal risk factors for childhood Type 1 diabetes in Western Australia, using a complete population-based cohort.

METHODS

Children born between 1980 and 2002 and diagnosed with Type 1 diabetes aged < 15 years (n = 940) up to 31 December 2003 were identified using a prospective population-based diabetes register with a case ascertainment rate of 99.8%. Perinatal data were obtained for all live births in Western Australia from 1980 to 2002 (n = 558 633) and record linkage performed to identify the records of cases.

RESULTS

The incidence of Type 1 diabetes increased by 13% for each 5-year increase in maternal age [adjusted incidence rate ratio (IRR) 1.13, 95% confidence interval (CI) 1.05, 1.21], by 13% for every 500-g increase in birth weight (adjusted IRR 1.13, 95% CI 1.04, 1.23). The incidence decreased with increasing birth order (adjusted IRR 0.89, 95% CI 0.82, 0.96) and increasing gestational age (adjusted IRR 0.84, 95% CI 0.77, 0.93). A higher incidence of Type 1 diabetes was associated with an urban vs. non-urban maternal address at the time of birth (adjusted IRR 1.38, 95% CI 1.18, 1.63), but no association was found with socio-economic status of the area.

CONCLUSIONS

A higher incidence of Type 1 diabetes was associated with increasing maternal age, higher birth weight, lower gestational age, lower birth order and urban place of residence at the time of birth.

Type 1 diabetes in Japan

Type 1 diabetes is a multifactorial disease which results from a T-cell-mediated autoimmune destruction of the pancreatic beta cells in genetically predisposed individuals. The risk for individuals of developing type 1 diabetes varies remarkably according to country of residence and race. Japan has one of the lowest incidence rates of type 1 diabetes in the world, and recognises at least three subtypes of the condition: acute-onset ('classical'), slow-onset, and fulminant type 1 diabetes. The incidence rate of type 1 diabetes in children aged 0-14 years in Japan increased over the period from 1973-1992, but remained constant over the last decade, averaging 2.37 cases per 100,000 persons per year; the incidence does not appear to have increased in older age groups. Although there are few reports regarding the incidence and prevalence of type 1 diabetes in adult-onset patients, it appears that the prevalence of type 1 diabetes in adults is more than twice that in childhood-onset patients and that two-thirds of them have a slow-onset form of type 1 diabetes. Differences and similarities in the association of MHC and non-MHC genes with type 1 diabetes are observed in Japan and in countries with Caucasoid populations. Highly susceptible class II HLA haplotypes identified in patients of Caucasoid origin are rarely seen in Japanese patients, whereas protective haplotypes are universal. Non-MHC genes associated with susceptibility to type 1 diabetes in both Japanese and Caucasoid patients include polymorphisms in the insulin gene, the cytotoxic T-lymphocyte antigen 4 (CTLA4) gene, the interleukin-18 (IL18) gene and the major histocompatibility complex class I chain-related gene A (MICA) gene. Fulminant type 1 diabetes is a unique subtype of type 1 diabetes that accounts for about 20% of acute-onset type 1 diabetes, and is seen mainly in adults. The challenge for the future is to investigate the underlying pathogenesis of beta cell destruction, including the genetic or environmental factors that may modify the form of onset for each subtype of Japanese type 1 diabetes.

HLA and autoimmune diseases: Type 1 diabetes (T1D) as an example

Autoimmune diseases need to be considered at a genetic and mechanistic level. T1D is an autoimmune, chronic, multifactorial and polygenic disease characterized by the destruction of the pancreatic beta-cells associated with long term dysfunction of several organs and tissues. Mechanisms of susceptibility include epi-genetic and post-transcriptional effects that regulate transmission and expression of the inherited genes. The HLA complex, constitutes the most relevant region contributing 50% of the inherited risk for T1D. An additional 17 genes with variable but small effects have been described. In non-Caucasians, the presence of E-DRbeta1-74 and/or D-DRbeta1-57 are relevant in predisposition. The "Diabetogenic haplotypes" in Mexicans were DRB1*0301-DQA1*0501-DQB1*0201 (OR = 21.4); DRB1*0405-DQA1-*0301-DQB1*0302 (OR = 44.5) and the same DQA1/DQB1 with DRB1*0404/*0401 conferring lower risk, increasing (OR = 61.3) with an early age at onset and a heterozygote DR3/DR4 genotype. In most populations, the absence of D-57 and the presence of R-52 are important to the susceptibility, but in Hispanics, all DR4s (including the protective DRB1*0403/*0407/*0411) are in linkage disequilibrium with DQA1/DQB1 susceptibility alleles. Thus, susceptibility alleles in Latin American Mestizos are of Mediterranean ancestry whereas protective alleles are of Amerindian origin. In this review, we discuss the complexity of T1D and some aspects of prevention/intervention based on immunogenetics.

Clinical skills: empowering people with diabetes to minimize complications

Diabetes mellitus is a lifelong condition. It represents a major cause of morbidity and mortality, often brought about by diabetic microvascular (retinopathy, nephropathy and neuropathy) and macrovascular (peripheral vascular disease, cardiovascular disease and stroke) complications. Although incurable, it is nevertheless possible for the person with diabetes to lead a normal life by adhering to a self-care management regimen. However, this complex, lifelong activity cannot be achieved in isolation. The role of the nurse, particularly as an educator and facilitator of learning, is therefore critical. This article aims to increase nurses' knowledge regarding the importance of ongoing education for the person with diabetes in order to minimize the development of microvascular and macrovascular complications. It also emphasizes the importance of including the individual in any decision-making process to ensure that empowerment is visible.

Incidence rate and spatio-temporal clustering of type 1 diabetes in Santiago, Chile, from 1997 to 1998

OBJECTIVE

To estimate the incidence rate of type 1 diabetes in the urban area of Santiago, Chile, from March 21, 1997 to March 20, 1998, and to assess the spatio-temporal clustering of cases during that period.

METHODS

All sixty-one incident cases were located temporally (day of diagnosis) and spatially (place of residence) in the area of study. Knox's method was used to assess spatio-temporal clustering of incident cases.

RESULTS

The overall incidence rate of type 1 diabetes was 4.11 cases per 100,000 children aged less than 15 years per year (95% confidence interval: 3.06 - 5.14). The incidence rate seems to have increased since the last estimate of the incidence calculated for the years 1986 - 1992 in the metropolitan region of Santiago. Different combinations of space-time intervals have been evaluated to assess spatio-temporal clustering. The smallest p-value was found for the combination of critical distances of 750 meters and 60 days (uncorrected p-value = 0.048).

CONCLUSIONS

Although these are preliminary results regarding space-time clustering in Santiago, exploratory analysis of the data method would suggest a possible aggregation of incident cases in space-time coordinates.

Prevalence of human leukocyte antigen DQA1 and DQB1 alleles in Kuwaiti Arab children with type 1 diabetes mellitus

The prevalence of human leukocyte antigen (HLA) DQB1 and DQA1 alleles has been determined in 78 Kuwaiti Arab children with insulin-dependent diabetes mellitus (IDDM) and in 57 normal healthy controls with similar ethnic background. The typing of HLA-DQ alleles was carried out using an allele-specific DNA-based polymerase chain reaction (PCR) SSP method. DR typing was also performed in 212 control subjects using PCR-SSP (sequence specific primer) method. A significantly higher frequency of DQB1*0201 allele was found in IDDM cases compared to the controls (p<0.001). There was no significant difference in the prevalence of DQB1 alleles *0302, *0501, and *0602 between IDDM cases and the controls. In contrast, DQB1 alleles *0301, *0402, *0502, *0602, and *0603 were represented at a somewhat higher frequency in controls compared to the IDDM cohort. The frequency of DQA1 allele *0301, which encode for an Arg at codon 52, was significantly higher in the IDDM patients compared to the controls (p<0.001). The frequency of DQA1 allele *0302 was also higher in IDDM cases than controls (p = 0.034) but the difference was less pronounced than DQA1*0301. Amongst the Arg52 alleles, no significant difference was detected in the frequency of *0401 between IDDM cases and the controls and the allele *0501 was detected only in controls. For non-Arg52 alleles *0103, *0104, and *0201, the differences in the two groups were not significant, with the exception of allele *0104 (p = 0.024). DR3 was the most common type in the Kuwaiti general population (28%) and DRB1*0301 was detected in 41% of the individuals with DR3 specificity. Analysis of HLA-DQBI/DQA1 haplotypes from IDDM cases and controls revealed a significantly high frequency of haplotype DQA1*0301/DQB1*0201 between Kuwaiti IDDM cases (49/78, 63%) and the controls (8/57, 14%).

Migrant populations and the incidence of type 1 diabetes mellitus: an overview of the literature with a focus on the Spanish-heritage countries in Latin America

Type 1 diabetes mellitus (DM) is a 'chronic' autoimmune disorder leading to the destruction of the pancreatic beta cell. The natural history of diabetes includes a long subclinical (prediabetes) period. The pathogenesis is multifactorial and characterized by the interaction of environmental factors, with predisposing genes, most of which are associated with the HLA DR DQ loci. The relatively recent development of worldwide incidence registries for Type 1 DM has allowed us to compare the epidemiological results obtained in most parts of the world. This approach is particularly valuable in analysing the effects of migration of populations from one area of the world where the incidence of Type 1 DM is different (usually lower) to a new geographic setting. Properly designed migrant studies may be valuable in uncovering whether the genetic background remains more important than the new 'exposure' as illustrated by the Sardinian migration to Lazio and Lombardy. The presence of some putative 'protective' environmental exposures or the absence of those prevalent in the country of origin may explain the usually lower Type 1 DM incidence observed in most countries (Chile, Peru, Mexico) sharing a 'Spanish caucasoid genetic pool', and even in relatively genetically homogeneous groups such as Japanese populations migrating to Hawaii. In fact, the disease is caused by both genetic and environmental factors and to convince the scientific community of this fact is a primary responsibility for epidemiologists.

Applicability of the case-parent design in the etiological research of Type 1 diabetes in Chile and other genetically mixed populations

In case-control studies, spurious associations between Human Leukocyte Antigen (HLA) alleles and Type 1 diabetes could arise as a result of population stratification, if there are ethnic differences between cases and non-related controls. The Chilean population has several unique features which make it ideal for the study of the effect of stratification by ethnicity on genetic epidemiological research. The incidence rates of Type 1 diabetes in Chilean Aboriginal populations are very low compared to Caucasian populations, while the frequency of the alleles in HLA loci also vary across ethnic groups. In order to avoid the confounding effect of ethnicity, one possible remedy would be the use of cases and their parents in place of non-related controls. The case-parent design offers an adequate framework for the study of the association between HLA polymorphisms and Type 1 diabetes in the Chilean population and can also be applicable to other genetically mixed populations especially in the Americas.

Amamentação ao seio, amamentação com leite de vaca e o diabetes mellitus tipo 1: examinando as evidências

A etiologia do diabetes mellitus tipo 1 (DM1) envolve tanto herança genética como a exposição a fatores ambientais. Evidências de estudos epidemiológicos e experimentais sugerem que a dieta pode ser importante na etiopatogenia dessa doença. Em 1984, Borch-Johnsen e col. sugeriram, com base nos resultados de um estudo caso-controle, que o leite materno seria um fator de proteção para o DM1; esse efeito se daria devido às propriedades anti-infecciosas desse tipo de leite, ou pelo fato de que a amamentação ao seio evitaria que as crianças pudessem ser precocemente expostas a outros agentes etiológicos contidos nos substitutos do leite materno. Esses mesmos achados foram poste-riormente encontrados em diversos estudos, mas o papel do leite materno no aparecimento do DM1 ainda permanece controverso. Em 1992, Karjalainen e col., ao compararem os soros de indivíduos com e sem DM1, observaram, entre os diabéticos, altas concentrações de anticorpos anti-albumina bovina. Os autores postularam a hipótese de que a albumina bovina poderia atuar como desencadeadora do processo destrutivo das células ß do pâncreas e, conseqüentemente, do diabetes. Resultados conflitantes foram observados nas publicações que se sucederam a essa. Neste artigo, resumem-se e discutem-se os achados de diferentes pesquisadores que investigaram a importância desses fatores dietéticos para o aparecimento do DM1.