Screening for the IDDM high-risk genotype. A rapid microtitre plate method using serum as source of DNA

Environmental trigger(s) of type 1 diabetes: why so difficult to identify?

Type 1 diabetes (T1D) is one of the most common chronic diseases with childhood onset, and the disease has increased two- to fivefold over the past half century by as yet unknown means. T1D occurs when the body's immune system turns against itself so that, in a very specific and targeted way, it destroys the pancreatic β-cells. T1D results from poorly defined interactions between susceptibility genes and environmental determinants. In contrast to the rapid progress in finding T1D genes, identification and confirmation of environmental determinants remain a formidable challenge. This review article will focus on factors which have to be evaluated and decision to take before starting a new prospective cohort study. Considering all the large ongoing prospective studies, new and more conclusive data than that obtained so far should instead come from international collaboration on the ongoing cohort studies.

HLA class I sequence-based typing using DNA recovered from frozen plasma

We describe a rapid, reliable and cost-effective method for intermediate-to-high-resolution sequence-based HLA class I typing using frozen plasma as a source of genomic DNA. The plasma samples investigated had a median age of 8.5 years. Total nucleic acids were isolated from matched frozen PBMC (~2.5 million) and plasma (500 μl) samples from a panel of 25 individuals using commercial silica-based kits. Extractions yielded median [IQR] nucleic acid concentrations of 85.7 [47.0-130.0]ng/μl and 2.2 [1.7-2.6]ng/μl from PBMC and plasma, respectively. Following extraction, ~1000 base pair regions spanning exons 2 and 3 of HLA-A, -B and -C were amplified independently via nested PCR using universal, locus-specific primers and sequenced directly. Chromatogram analysis was performed using commercial DNA sequence analysis software and allele interpretation was performed using a free web-based tool. HLA-A, -B and -C amplification rates were 100% and chromatograms were of uniformly high quality with clearly distinguishable mixed bases regardless of DNA source. Concordance between PBMC and plasma-derived HLA types was 100% at the allele and protein levels. At the nucleotide level, a single partially discordant base (resulting from a failure to call both peaks in a mixed base) was observed out of >46,975 bases sequenced (>99.9% concordance). This protocol has previously been used to perform HLA class I typing from a variety of genomic DNA sources including PBMC, whole blood, granulocyte pellets and serum, from specimens up to 30 years old. This method provides comparable specificity to conventional sequence-based approaches and could be applied in situations where cell samples are unavailable or DNA quantities are limiting.

Islet autoantibody development during follow-up of high-risk children from the general Norwegian population from three months of age: design and early results from the MIDIA study

We describe the design of the MIDIA study and present serial islet autoantibody data from 3 months of age in the 526 first enrolled children from the general population carrying the type 1 diabetes high-risk HLA-DRB1*0401-DQA1*03-DQB1*0302/DRB1*0301-DQA1*05-DQB1*02 genotype. Blood samples were obtained from children at ages 3, 6, 9 and 12 months and annually thereafter to a median age of 12 months. Autoantibodies to insulin, glutamic acid decarboxylase and insulinoma-associated antigen-2 were measured with radiobinding assays. About 25,000 general population newborns were genotyped, and among 526 children with the high-risk HLA genotype, 2104 samples were assayed. Fourteen children were positive in at least two consecutive samples, including 12 who were positive for > or =2 autoantibodies at least once, of which five developed type 1 diabetes at median age 15.3 months. Seven of 14 persistently positive children seroconverted before 9 months, including two before 6 months of age. The estimated cumulative probability of multiple autoantibody positivity at 5 years was 7.3% (95% confidence interval: 3.5-12.4%). Thus, persistent islet autoimmunity is not uncommon in the first year of life in children from the general population carrying the high-risk HLA genotype, and may develop as early as at 6 months of age.

Spatiotemporal trends and age-period-cohort modeling of the incidence of type 1 diabetes among children aged <15 years in Norway 1973-1982 and 1989-2003

OBJECTIVE

We have investigated age-period-cohort effects and spatial and temporal trends for the incidence of type 1 diabetes among 0- to 14-year-old children in Norway.

RESEARCH DESIGN AND METHODS

We included children with the diagnosis of type 1 diabetes in Norway during 1973-1982 and 1989-2003. We studied age, calendar period, and birth cohort effects using Poisson regression, including Holford's method of parameterization, to model the dependencies between age, period, and cohort effects. To study spatiotemporal clustering of cases, we used spatial scan statistics.

RESULTS

The overall incidence rate for the study population <15 years of age was 22.7 cases per 100,000 (95% CI 22.1-23.4), showing an average annual increase of 1.2% (95% CI 0.7-1.5%) during the study period. One specific area with 30% increased incidence rates was identified in the southern part of Norway during 1976-1980 (P = 0.001). Also, children born during 1964-1966 in a specific region in the southern part of Norway as well as children born during 1987-1989 in a region in northern Norway showed 2.0 and 2.6 times, respectively, higher incidence rates compared with the rest of the country (both P = 0.001).

CONCLUSIONS

The incidence of type 1 diabetes among children increased during the study period. Birth cohort effects were identified using the spatiotemporal scan statistic but not using age, period, and birth cohort modeling. Such effects, within the relatively homogenous Norwegian population, suggest the influence of nongenetic etiological factors.

High prevalence of human enterovirus a infections in natural circulation of human enteroviruses

Human enterovirus (HEV) infections can be asymptomatic or cause only mild illness; recent evidence may implicate HEV infection in type 1 diabetes mellitus and myocarditis. Here, we report the molecular characterization of HEV obtained in serial monthly collections from healthy Norwegian infants. A total of 1,255 fecal samples were collected from 113 healthy infants beginning at age 3 months and continuing to 28 months. The samples were analyzed for HEV nucleic acid by real-time PCR. Fifty-eight children (51.3%) had HEV infections. One hundred forty-five positive samples were typed directly by nucleotide sequencing of the VP1 region. HEV-A was detected most frequently, with an overall prevalence of 6.8%. HEV-B was present in 4.8% of the samples and HEV-C in only 0.2% of the samples. No poliovirus or HEV-D group viruses were detected. Twenty-two different serotypes were detected in the study period: the most common were EV71 (14.5%), CAV6 (10.5%), CAV4 (8.9%), E18 (8.9%), and CBV3 (7.3%). These findings suggest that the prevalence of HEV infections in general, and HEV-A infections in particular, has been underestimated in epidemiological studies based on virus culture.

Longitudinal observation of enterovirus and adenovirus in stool samples from Norwegian infants with the highest genetic risk of type 1 diabetes

BACKGROUND

Enterovirus and adenovirus are common in infancy, causing mostly asymptomatic infections. However, even an asymptomatic infection may be associated with increased risk of development of certain chronic non-infectious diseases, as has been suggested for enterovirus and type 1 diabetes. Data on occurrence and course of the infections in infancy are therefore important for designing effective approaches towards study of the association.

OBJECTIVES

To estimate the frequency of enterovirus and adenovirus infections in Norwegian infants, to evaluate the duration of the infections, to investigate their association with symptoms, and to establish a robust procedure that will be used to study the association between these viruses and the development of auto-immunity leading to type 1 diabetes.

STUDY DESIGN

Parents of infants, recruited for a study on environmental triggers of type 1 diabetes, submitted monthly samples of infant faeces, as well as information on symptoms of infection. The samples were analysed for enterovirus and adenovirus using quantitative real-time PCR, and enterovirus-positive samples were sequenced.

RESULTS

Enteroviruses were found in 142/1,255 (11.3%), and adenoviruses in 138/1,255 (11.0%) of stool samples. Approximately half of the infants were exposed to these viruses at least once during the first year of observation (period 3-14 months of age). The presence of adenovirus was associated with fever and with symptoms of cold but not with diarrhoea and vomiting. The enterovirus positivity was not associated with any symptoms.

CONCLUSIONS

The prevalence of enterovirus and adenovirus in longitudinally obtained faecal samples from infants is sufficiently high to enable studies of their association with chronic diseases. The present protocol for evaluating exposure to these viruses is well suited for large-scale efforts aimed at assessing possible long-term consequences, particularly in relation to type 1 diabetes.

Genetics for targeting disease prevention: diabetes

This article provides an overview of current thinking regarding genetics and diabetes (type 1, type 2, and gestational diabetes mellitus),including a selective look at a few implicated gene variants. This article explores how this information might be applied in current and future clinical practice to (1) predict who is at risk for diabetes and its complications, (2) identify and intervene to prevent or delay the development of diabetes in persons at risk, (3) identify patients with diabetes in an early stage and intervene to prevent later complications,and (4) individualize therapy for patients with diabetes to improve outcomes. The article concludes with some general thoughts about genetics and diabetes prevention in the future.

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.

HLA class II typing in newborns reveals a low frequency of the DRB1*04 allele and a high frequency of DRB1*11 allele in three regions of continental Italy

As part of a longitudinal study aimed at defining the natural history of prediabetic autoimmunity and predicting the risk of future cases of type 1 diabetes, 3607 newborns from three regions of continental Italy (Lombardia, Liguria, and Lazio) were subjected to genetic testing to determine human leukocyte antigen-DRB1 (HLA-DRB1) and -DQB1 allele and phenotype frequencies. Polymerase chain reaction and immobilized sequence-specific oligonucleotide probe assays were used to identify ten DRB1 allele lineages and three DQB1 alleles. No major inter-regional differences emerged in the allelic distribution indicating homogeneous distribution of the HLA DRB1-DQB1 alleles among the three regions analyzed. Comparison of our data with those published for other Caucasian populations reveals that these three regions are characterized by a very low frequency of DRB1*04 (8%) and a high frequency of DRB1*11 (25%). The phenotype frequencies of HLA-DQB1*0302 and DQB1*0602 observed are also lower than those reported for other populations. Furthermore, the DRB1*04-DQB1*0302 haplotype was relatively infrequent in our population (5.3% of the newborns tested). These findings furnish a genetic "portrait" of the populations of the analyzed regions that will be useful not only for investigation of the genetic risk of type 1 diabetes mellitus in Italy but also for studies of other autoimmune diseases related to HLA genotypes.

High-risk genotype for type 1 diabetes: a new simple microtiter plate-based ELOSA assay

The main contribution to genetic susceptibility for type 1 diabetes (T1D) is conferred by the HLA class II genes, with a major involvement of the DQB1*02 and 0302 alleles. The aim of our study was to develop a simple and rapid method suitable for identifying individuals with an HLA-associated T1D risk using whole blood as a source of DNA and reverse hybridization on microtiter plates (ELOSA). DNA was extracted from whole blood using various extraction methods. The PCR-amplified second exon of the DQB1 gene was hybridized at 37 degrees C for 1 hr to a set of 11 capture probes immobilized on a microtiter plate (eight-well strip per test) and corresponding to T1D susceptibility (S), protection (P), or neutral (N) alleles. Colorimetric analysis was then performed using specific oligonucleotides coupled to horseradish peroxidase and OrthoPhenyl Peroxidase (OPD) substrate. DNA samples corresponding to French (Rhône-Alpes area) T1D patients (n = 128) have been genotyped with the HLA-T1D prototype. A strong correlation is observed between susceptible genotypes and the disease, because 92.2% of the T1D individuals screened have at least one susceptible allele (DQB1*02 or *0302), thereby strengthening interest in analyzing DQB1 alleles as HLA-linked T1D markers in our Rhône-Alpes area population. Interestingly, clear T1D-associated genotyping results have been observed when using DNA samples extracted from dried blood spots, making it possible to envisage such genotyping in geographically dispersed affected families, for large-scale newborn screening, and for the inclusion of high-risk patients in clinical trials aimed at preventing the disease.

[Association of class II HLA antigens and insulin-dependent diabetes mellitus in the population of Vojvodina]

INTRODUCTION

Class II HLA antigens were investigated in a group of 28 patients with insulin-dependent diabetes mellitus (IDDM) and 218 healthy unrelated persons (control group) from Vojvodina.

MATERIAL AND METHODS

We used a modified two-colour immunofluorescence method (serologic technique) to determine the phenotype of DR and DQ locus HlA antigens. Phenotype frequencies of class II HLA antigens were determined in both investigated groups and were used for calculating relative risk (RR). If RR was higher than 1, we calculated the population attributable risk (EF), and if RR was lower than 1, we calculated the preventive fraction (PF). Investigation of statistically significant differences in frequencies of class II HLA antigens in patients and control group was performed by using chi 2 test.

RESULTS

Results of investigation showed that values of RR were higher than 1 for HLA DR4 (2,808), DR10 (1,116) and DQ3 (1,386), while we noticed a statistically significant difference in frequencies of HLA DR4 (chi 2 test: 4,805) in patients regarding control group. HLA DQ1 antigen has a preventive role in development of IDDM due to highest value of PF (0,314).

CONCLUSION

Results of our investigation confirm that there is an association of HLA DR4 with IDDM in population of Vojvodina. High values of relative risk of IDDM, noticed in persons with HLA-DR4 antigen, point to the degree of risk of IDDM, which is a disease with great socioeconomic importance in Vojvodina.

Acidic drinking water and risk of childhood-onset type 1 diabetes

OBJECTIVE

To estimate the associations of acidity and concentration of selected minerals in household tap water with the risk of type 1 diabetes.

RESEARCH DESIGN AND METHODS

We designed a population-based case-control study with 64 cases of type 1 diabetes and 250 randomly selected control subjects. Acidity, color, and mineral content were measured in tap water from each participant's household.

RESULTS

Tap water pH 6.2-6.9 was associated with a fourfold higher risk of type 1 diabetes compared with pH > or =7.7 (OR 3.73, 95% CI 1.52-9.15). This result was similar after exclusion of individuals with the highly protective HLA-DQB1*0602 allele, but adjustment for maternal education, urban/rural residence, sex, and age tended to strengthen the estimated association. Higher tap water concentration of zinc was associated with lower risk of type 1 diabetes after adjustment for pH and other possible confounders, but the overall association was strictly not significant.

CONCLUSIONS

These results suggest the possibility that quality of drinking water influences the risk of type 1 diabetes. The possible mechanisms by which water acidity or mineral content may be involved in the etiology of type 1 diabetes remain unknown, but the mechanisms are most likely indirect and may involve an influence on survival of microorganisms in the water.

DNA extraction and HLA genotyping using mailed mouth brushes from children

The need for blood samples in genetic epidemiologic studies often leads to low response rate among non-diseased individuals, and the collection of blood samples is costly and labor-intensive. We tested the feasibility of extracting DNA for human leukocyte antigen (HLA) typing from buccal cells collected with mailed, self-administered mouth brushes. A random sample of 1474 Norwegian children aged 0-17 yr was contacted by mail and received information about the study and mouth brushes for buccal cell samples. Brushes were returned by mail, DNA was extracted and the HLA-DQA1 and -DQB1 allelic polymorphisms were determined using polymerase chain reaction (PCR) and sequence-specific oligonucleotide probes. Mouth swabs were returned from 1068 (72.5%). Of these, DNA was extracted and HLA typing successfully completed for 1056 individuals (98.9%). In conclusion, we have described an efficient and safe set of methods for application in genetic epidemiologic studies of type 1 diabetes and other HLA-related diseases. A large proportion of randomly selected children returned self-administered mouth swabs with DNA of sufficient quality and quantity for HLA genotyping.

Diabetes-associated HLA-DQ genes and birth weight

An association has recently been described between increased birth weight and increased risk of childhood-onset type 1 diabetes. Whether this relationship is explained by genes associated with both increased birth weight and increased risk of type 1 diabetes is unknown. In the present study, we tested the association between birth weight and HLA-DQ genotypes known to confer risk for type 1 diabetes among 969 nondiabetic children randomly selected from the Norwegian population. We found that HLA genotypes previously shown to confer risk for type 1 diabetes were associated with reduced birth weight (the mean difference in birth weight between the DQB1*0602/DQB1*0602 and DQ8/DQ2 genotypes was 354 g [95% CI 105-604]), which was opposite of that expected if HLA genes explained the birth weight-type 1 diabetes association.