Serum alpha- and gamma-tocopherol concentrations and risk of advanced beta cell autoimmunity in children with HLA-conferred susceptibility to type 1 diabetes mellitus

AIMS/HYPOTHESIS

The aim of our study was to assess the associations of serum alpha- and gamma-tocopherol concentrations with the risk of advanced beta cell autoimmunity in children with HLA-conferred genetic susceptibility to type 1 diabetes mellitus.

METHODS

A case-control study with 108 cases with advanced beta cell autoimmunity and 216 matched control participants nested within the birth cohort of the Type 1 Diabetes Prediction and Prevention Project. A serum sample for vitamin E analyses was collected from all the children in the cohort at the age of 1 year and thereafter at 12 month intervals. For each case-control group, all the repeated serum samples up to the age of seroconversion to autoantibody positivity in the case were analysed. A conditional logistic regression model was used to determine potential associations between seroconversion and serum tocopherol concentrations.

RESULTS

Serum alpha- or gamma-tocopherol concentrations were not significantly associated with the risk of advanced beta cell autoimmunity. The odds ratio (95% CI) for micromol/l increase in serum concentration of the first-year sample was 0.97 (0.92-1.03) for alpha-tocopherol and 1.10 (0.70-1.74) for gamma-tocopherol. However, there was an interaction between high values of gamma-tocopherol at the age of 1 year and the time of seroconversion (p = 0.024).

CONCLUSIONS/INTERPRETATION

It seems unlikely that high concentrations of alpha- or gamma-tocopherol protect against advanced beta cell autoimmunity in young children.

Prediction of type 1 diabetes among siblings of affected children and in the general population

AIMS/HYPOTHESIS

To compare the predictive characteristics of autoantibodies to GAD (GADA) and islet antigen 2 (IA-2A) for type 1 diabetes between siblings of affected children and children from the general population.

METHODS

Seven-hundred and fifty-five siblings and 3,475 population-derived children were screened for GADA and IA-2A and observed for type 1 diabetes for 15 years. Sensitivity and cumulative disease risks from GADA, IA-2A and double positivity were compared between the cohorts.

RESULTS

Fifty-six siblings (7.4%) tested positive for GADA, 39 (5.2%) for IA-2A and 29 (3.8%) for both autoantibodies. Thirty-four population derived participants (1.0%) had GADA, 22 (0.6%) had IA-2A and 7 (0.2%) had double positivity. Fifty-one siblings (6.8%) and 15 participants in the population cohort (0.4%) progressed to type 1 diabetes. The predictive sensitivity of GADA was 68% (95% CI 53-81%) among siblings and 50% (95% CI 23-77%) in the general population, while the corresponding values were 58 (95% CI 43-72%) and 43% (95% CI 18-71%) for IA-2A. Double-autoantibody positivity had a sensitivity of 48% (95% CI 34-63%) among siblings and 36% (95% CI 13-65%) in the population cohort. Cumulative disease risks from GADA, IA-2A and double positivity were, respectively, 61% (95% CI 48-74%), 74% (95% CI 61-88%) and 83% (95% CI 69-97%) among siblings compared with those of 24% (95% CI 9-38%), 32% (95% CI 12-51%) and 86% (95% CI 60-100%) in the general population.

CONCLUSIONS/INTERPRETATION

There were no significant differences in the disease-predictive sensitivity of GADA and IA-2A positivity or their combination between siblings and the population cohort, whereas, for each antibody, positivity was associated with a higher cumulative disease risk among siblings. Double-antibody positivity conferred similar cumulative disease risk both among siblings and in the general population.

Age at introduction of new foods and advanced beta cell autoimmunity in young children with HLA-conferred susceptibility to type 1 diabetes

AIMS/HYPOTHESIS

Evidence for the role of infant feeding in the development of beta cell autoimmunity is inconsistent. We set out to study the effects of breastfeeding and of age at introduction of supplementary foods on the development of beta cell autoimmunity.

SUBJECTS AND METHODS

A prospective birth cohort of 3,565 infants with HLA-DQB1-conferred susceptibility to type 1 diabetes was recruited between 1996 and 2001 from two university hospital areas in Finland. Blood samples were collected at 3- to 12-month intervals to measure antibodies against islet cells, insulin, glutamate dehydroxylase and islet antigen 2. The families kept a record on the age at introduction of new foods, and for each visit completed a structured dietary questionnaire. The endpoint was repeated positivity for islet cell antibodies together with at least one of the other three antibodies.

RESULTS

The overall or exclusive duration of breastfeeding was not associated with the risk of developing the endpoint. An early age at introduction of fruits and berries (< or =4 months) was related to increased risk of developing positivity for the endpoint (hazard ratio [95% CI] for earliest tertile 2.02 [1.03-3.95] and for midtertile 1.97 [1.06-3.64] compared with latest tertile >4 months). Also, introducing roots between 3 and 3.9 months (midtertile) was related to increased risk of the endpoint (hazard ratio [95% CI] for the earliest tertile 1.04 [0.57-1.90] and for midtertile 1.82 [1.19-2.79] compared with latest tertile). These associations were independent of several putative socio-demographic and perinatal confounding factors.

CONCLUSIONS/INTERPRETATION

Our findings suggest that an early age at introduction of fruits and berries and roots associates independently with beta cell autoimmunity, contradicting earlier findings from smaller birth cohort studies.

Intake of vitamin D by Finnish children aged 3 months to 3 years in relation to sociodemographic factors

OBJECTIVE

To study the total daily intake of vitamin D from food and supplements among Finnish children aged 3 months to 3 years, the dietary sources of vitamin D and the association between vitamin D intake and sociodemographic factors.

SUBJECTS AND METHODS

The subjects are participants in the Finnish Type I Diabetes Prediction and Prevention Nutrition Study born between October 1997 and October 1998. At the age of 3 and 6 months, 1, 2 and 3 years, 342 (72% of the invited families), 298 (63%), 267 (56%), 233 (49%) and 209 (44%) families, respectively, participated in the present study. Food consumption was assessed by a 3-day food record. A structured questionnaire was used to record the parents' socioeconomic status.

RESULTS

The mean dietary vitamin D intake exceeded the recommendation (10 microg/day) at the age of 3 (11.0 microg) and 6 months (12.0 microg), but decreased thereafter being 9.8, 5.0 and 4.1 microg at 1, 2 and 3 years of age, respectively. Among the children 91, 91, 81, 42 and 26% used vitamin D supplements at the age of 3 and 6 months, and 1, 2 and 3 years, respectively. In children not using vitamin D supplements, vitamin D intake was less than 10 microg/day at all ages. Vitamin D intake from food did not differ in children who used and did not use vitamin D supplements. Vitamin D supplements were the main source of vitamin D intake in all age groups studied, followed by vitamin D-fortified infant formula in 3-month-olds and infant formula and baby foods in 6-month-olds. After the age of 1 year, the most important food sources of vitamin D were margarine, fish, baby foods, low-fat milk and eggs. Sociodemographic factors, especially the number of children in the family and maternal age, were associated with the total vitamin D intake and vitamin D supplement use.

CONCLUSION

Vitamin D supplements are not used according to the dietary recommendations in a substantial proportion of Finnish children.

Lymphoid tyrosine phosphatase (LYP/PTPN22) Arg620Trp variant regulates insulin autoimmunity and progression to type 1 diabetes

AIMS/HYPOTHESIS

We analysed the contribution of the lymphoid protein tyrosine phosphatase (LYP) Arg620Trp variant (which corresponds to the PTPN22 C1858T polymorphism) to the emergence of beta-cell-specific humoral autoimmunity and progression to type 1 diabetes in man. We also explored the heterogeneity in the disease-predisposing effect of this polymorphism in relation to known disease loci, sex and age at disease onset.

SUBJECTS AND METHODS

A population-derived Finnish birth cohort with increased disease susceptibility conferred by HLA-DQB1 was monitored for the appearance of islet cell autoantibodies, and individuals found to be positive were tested for autoantibodies against insulin (IAA), glutamic acid decarboxylase and islet antigen-2 (n = 574; mean follow-up time 4.9 years). Gene interaction effects on disease susceptibility were analysed in case-control and family series (546 patients, 538 controls, 245 nuclear families). All subjects were typed for HLA DR-DQ, insulin gene (INS), CTLA4 and PTPN22 C1858T polymorphisms.

RESULTS

The PTPN22 1858TT genotype was associated with the appearance of IAA (adjusted hazard ratio = 4.6, 95% CI 2.4-9.0; p = 0.000013). PTPN22, INS and HLA-DRB1 had an additive effect on the emergence of IAA. The 1858TT and CT genotypes conferred an increased risk of developing additional autoantibodies or clinical disease (hazard ratio=4.1, 95% CI 1.5-11.6; and 1.6, 95% CI 1.1-2.4, respectively; p = 0.003). The strong effect of PTPN22 on disease susceptibility (p = 2.1 x 10(-8)) was more pronounced in males (p = 0.021) and in subjects with non-DR4-DQ8/low-risk HLA genotypes (p = 0.0004).

CONCLUSIONS/INTERPRETATION

In the pathogenesis of type 1 diabetes the underlying mechanism of the PTPN22 C1858T polymorphism appears to involve regulation of insulin-specific autoimmunity. Importantly, it strongly affects progression from prediabetes to clinical disease.

The effect of HLA class II, insulin and CTLA4 gene regions on the development of humoral beta cell autoimmunity

AIMS/HYPOTHESIS

The aim of this study was to explore the contribution of genetic factors to the emergence of beta-cell-specific humoral autoimmunity.

SUBJECTS AND METHODS

We analysed the effect of HLA class II, insulin (INS; -23 HphI variant) and cytotoxic T-lymphocyte-associated protein 4 (CTLA4 [+49 and CT60]) genes on the appearance of beta-cell-specific autoantibodies in a large population-based birth cohort recruited in Finland. Infants carrying increased risk HLA DQB1 genotypes were monitored for the appearance of autoantibodies (islet cell autoantibodies [ICA], insulin autoantibodies [IAA], glutamic acid decarboxylase autoantibodies [GADA] and islet antigen 2 antibodies [IA-2A]). Those who developed beta-cell-specific autoantibodies were studied (n=574, mean follow-up time: 4.9 years; range 0.5-9.3).

RESULTS

IAA emerged at a higher rate in children with the -23 HphI AA INS genotype than in those carrying AT or TT variants (hazard ratio 2.1, 95% CI 1.4-2.9, p<0.001). This effect of the INS locus was present in both HLA DQB1 risk groups. The appearance of IAA showed a strong association also with the HLA DRB1*0401 allele (hazard ratio 13.1, 95% CI 1.8-93.4, p<0.001). The development of IA-2A was also somewhat accelerated by the DRB1*0401 variant (p=0.03). Isolated ICA positivity was independent of the HLA and INS genotypes. None of the humoral immune markers showed association with the CTLA4 gene.

CONCLUSIONS/INTERPRETATION

The INS and the DRB1 loci appear to contribute to the pathogenesis of type 1 diabetes by initiating/modifying insulin-specific autoimmunity. The emergence of IAA represents a crucial step in the development of beta cell autoimmunity in young children, in whom the appearance of GADA and IA-2A is linked to IAA.

Dynamics of diabetes-associated autoantibodies in young children with human leukocyte antigen-conferred risk of type 1 diabetes recruited from the general population

This study characterized the dynamics of islet cell antibodies (ICA), insulin antibodies (IAA), glutamic acid decarboxylase antibodies (GADA), and IA-2 antibodies (IA-2A) in 1006 children recruited from the general population due to human leukocyte antigen (HLA) DQB1-conferred risk for type 1 diabetes (T1D). By the age of 5 yr, 13.8% of the children had had one or more autoantibodies in at least one sample drawn at 3- to 12-month intervals from birth, whereas 6.1% had had one or more of the three autoantibodies to biochemically defined antigens in at least two consecutive samples. The cumulative frequencies of positivity for at least two antibodies ranged from 3.2-4.4%. Seventy-five children (7.5%) had at least once ICA, 83 (8.3%) had IAA, 46 (4.6%) had GADA, and 33 (3.3%) had IA-2A. IAA were transient more frequently than the other antibodies (P < or = 0.03) and fluctuated between positivity and negativity more often than ICA (P = 0.001). The genetically high risk children were positive for each autoantibody reactivity more often (P < or = 0.03) than the moderate risk subjects. Thirteen of the 1006 children (1.3%) presented with T1D by the age of 5 yr. The most sensitive predictors of T1D were ICA and IAA, whereas the most specific predictor was IA-2A. Positivity for at least two autoantibodies of IAA, GADA, and IA-2A had the highest positive predictive value for T1D (34%). We conclude that the frequency of various diabetes-associated autoantibodies increases at a relatively stable rate at least up to the age of 5 yr. Persistent positivity for two or more autoantibodies appears to reflect destructive progressive beta-cell autoimmunity, whereas positivity for a single autoantibody may represent harmless nonprogressive or even regressive beta-cell autoimmunity.

A linkage analysis of the CTLA4 gene region in Finnish patients with type 1 diabetes

The cytotoxic T-lymphocyte antigen 4 (CTLA4) region on 2q33 has been shown to be linked to, and associated with, type 1 diabetes (T1D) and suggested to be one of the loci contributing to diabetes aetiology. The polymorphisms responsible for the effect are yet not defined, and the findings reported for the known markers have been discrepant in various populations. We analysed 15 markers around the CTLA4 gene in 138 Finnish affected sib-pair families. A maximum multipoint LOD score (MMLS) of 0.83 at the CTLA4-(AT)n microsatellite was obtained for the whole data set. When stratified, the MMLS increased to 2.61 in the IBS2 (identical by state 2) dataset. In a transmission/disequilibrium test (TDT), some sex-specific effects were observed in transmissions of alleles of CTLA4-(AT)n and D2S105 in siblings. The transmission of the CTLA4 +49 A/G single nucleotide polymorphism (SNP) did not deviate from the expected frequency in this study. In conclusion, our study confirms the linkage of the CTLA4 region to T1D in the Finnish population. In addition, the observations suggest that the polymorphism actually involved in the disease is not the CTLA4 +49 A/G SNP but a polymorphism in linkage disequilibrium with CTLA4 markers and probably closer to CTLA4-(AT)n than to the CTLA4 +49 A/G SNP.

HLA DR-DQ-encoded genetic determinants of childhood-onset type 1 diabetes in Finland: an analysis of 622 nuclear families

The diabetes predisposing effect of HLA genes is defined by a complex interaction of various haplotypes. We analyzed the disease association of HLA DRB1-DQA1-DQB1 genotypes in a large nuclear family cohort (n = 622) collected in Finland. Using the affected family based artificial control approach we aimed at characterizing all detectable disease-specific HLA haplotype and genotype effects. The DRB1*0401-DQB1*0302 haplotype was the most prevalent disease susceptibility haplotype in the Finnish population followed by (DR3)-DQA1*05-DQB1*02 and DRB1*0404-DQB1*0302. DRB1*0405-DQB1*0302 conferred the highest disease risk, although this haplotype was very rare. The DRB1*04-DQB1*0304 was also associated with increased disease risk, an effect detected for the first time in the Finnish population. The following haplotypes showed significant protection from the disease and are listed in decreasing order of the strength of their effect: (DR7)-DQA1*0201-DQB1*0303, (DR14)-DQB1*0503, (DR15)-DQB1*0602, DRB1*0403-DQB1*0302, (DR13)-DQB1*0603, (DR11/12/13)-DQA1*05-DQB1*0301, (DR1)-DQB1*0501. In addition to the DRB1*0401/0404-DQB1*0302/(DR3)-DQA1*05-DQB1*02 genotype and DRB1*04-DQB1*0302 homozygous genotypes, heterozygous combinations DRB1*0401-DQB1*0302/(DR13)-DQB1*0604, approximately /(DR8)-DQB1*04, approximately /(DR9)-DQA1*03-DQB1*0303, approximately /(DR1)-DQB1*0501 and approximately /(DR7)-DQA1*0201-DQB1*02 were also disease-associated. As a new finding in this population, the (DR3)-DQA1*05-DQB1*02 homozygous and (DR3)-DQA1*05-DQB1*02/(DR9)-DQA1*03-DQB1*0303 heterozygous genotypes conferred disease susceptibility. Similarly, the DRB1*0401-DQB1*0302/(DR13)-DQB1*0603 genotype was disease predisposing, implying that DQB*0603-mediated protection from diabetes is not always dominant. Comparison of our findings with published data from other populations indicates a significant disease-specific heterogeneity of the (DR8)-DQB1*04, (DR7)-DQA1*0201-DQB1*02 and (DR3)-DQA1*05-DQB1*02 haplotypes.

Temporal changes in the frequencies of HLA genotypes in patients with Type 1 diabetes--indication of an increased environmental pressure?

AIMS/HYPOTHESIS

The incidence of Type 1 diabetes has increased 2.5 times during the time period from 1966 to 2000 in Finland-a general trend seen in almost all developed countries that can only be explained by environmental factors. The aim of this study was to test the possible effect of a changing environment on distribution of genotypes associated with disease susceptibility.

METHODS

HLA DRB1-DQA1-DQB1 genes and two diabetes-associated polymorphisms at IDDM2 and IDDM12 were analyzed. The frequencies of genotypes were compared between cases diagnosed with childhood-onset Type 1 diabetes during the period of 1939-1965 (n=367) and those diagnosed between 1990 and 2001 (n=736). Chi-square statistics or the Fisher's Exact test were used for the comparison of frequencies of analyzed haplotypes and genotypes in the two groups.

RESULTS

The frequencies of (DR3) -DQA1*05-DQB1*02 and (DR4) -DQB1*0302 risk haplotypes and the high risk (DR3) -DQA1*05-DQB1*02/DRB1*0401-DQB1*0302 genotype were higher while proportion of patients carrying protective haplotypes-(DR15) -DQB1*0602 and (DR1301) -DQB1*0603-or protective genotypes was lower in patients diagnosed before 1965 as compared to those who developed disease after 1990. No temporal variation was found in the frequencies of genotypes at IDDM2 and IDDM12.

CONCLUSION/INTERPRETATION

Our data suggest that the need for genetic susceptibility to develop Type 1 diabetes has decreased over time due to an increasing environmental pressure and this results in a higher disease progression rate especially in subjects with protective HLA genotypes.

First-phase insulin response in young healthy children at genetic and immunological risk for Type I diabetes

AIMS/HYPOTHESIS

A reduced first-phase insulin response to intravenous glucose is perceived as a sign of far-advanced deterioration of beta-cell function during the development of Type I (insulin-dependent) diabetes mellitus, but data on insulin responses at the onset of diabetes-related autoimmunity are lacking. We studied the first-phase insulin responses of small children soon after observed seroconversion to autoantibody positivity.

METHODS

In the Type I Diabetes Prediction and Prevention Study newborn infants are screened for HLA-DQB1-associated genetic risk for Type I diabetes and those with increased risk are followed-up for the emergence of islet-cell antibodies. If antibodies are detected, autoantibodies to three other antigens (insulin, GAD65 and IA-2) are also measured. To measure first-phase insulin responses, intravenous glucose tolerance tests were carried out in 52 (1 to 5-year-old) children who had recently seroconverted to islet-cell antibody positivity.

RESULTS

The first-phase insulin response was subnormal (<38 mU/l, the 5(th) percentile of insulin responses of 20 islet-cell antibody negative healthy children at this age) in 22 of the 52 children (42%). Stepwise multiregression analysis showed that islet-cell antibody greater than 20 JDFU (p=0.0005), insulin autoantibodies (p=0.0009) and an increasing number of positive autoantibodies (p=0.0011) were independent predictors of low first-phase insulin response.

CONCLUSION/INTERPRETATION

A decreased first-phase insulin response could be an early phenomenon in the course of prediabetes in young children, implying a rapid autoimmune destruction or loss of function of beta cells as well as possible metabolic compensation mechanisms, since 11 out of the 22 high risk children remain nondiabetic for a considerable period of time despite low insulin responses.

No evidence of a functionally significant polymorphism of the BCL2 gene in Danish, Finnish and Basque type 1 diabetes families

Accumulating evidence has suggested a role for the anti-apoptotic protein BCL2 in the development of autoimmune diseases, including type 1 diabetes mellitus (T1DM). Recently, the first BCL2 polymorphism (Ala43Thr) with association to T1DM in a Japanese population was reported. The polymorphism was found significantly more frequent in control individuals (14.5%) than in T1DM patients (6.8%), and was furthermore found to be functionally relevant, promoting a increased sensitivity to apoptosis when overexpressed in an IL-7 dependent mouse pre-B cell line. To investigate the relevance of the polymorphism in Caucasians, we have genotyped nearly 1400 individuals comprising Danish, Finnish and Basque T1DM family materials, using a PCR-based RFLP assay. In contrast to what was observed in Japanese diabetic/control individuals, we find no evidence for association of the BCL2 Ala43Thr polymorphism to T1DM in Danish, Finnish and Basque Type 1 diabetes families.

Non-class II HLA gene associated with type 1 diabetes maps to the 240-kb region near HLA-B

Several studies provide evidence that in addition to the DQ-DR genes, HLA contains another uncharacterized gene or genes associated with type 1 diabetes. Our aim was to investigate the effect of this gene independently of the DQ-DR genes and to localize it with a matched case-control study. More than 1,400 patients and 30,000 control individuals from Finland were studied. They were first genotyped for the selected alleles of the HLA-DQB1, -DQA1, and -DRB1 genes. For the DR3/4(0404) genotype, 75 patients and 181 control subjects were stratified, and 241 patients and 354 controls were stratified for the DR3/4(0401) genotype. Ten microsatellite markers in the HLA class III and I regions (D6S273, TNFa, C12A, STR MICA, MIB, C125, C143, C245, C3211, and MOGc) and selected alleles of the HLA-A and HLA-B genes were studied. In the DR3/4(0404)-stratified group, we found that markers located between C12A and C143 near the HLA-B gene confer a strong additional diabetes association. This was confirmed by the population differentiation test in both DR3/4(0404)- and DR3/4(0401)-stratified groups. Our data indicate that an additional gene associated with type 1 diabetes is located in the 240-kb region near HLA-B. We excluded STR MICA polymorphism as a mutation responsible for diabetes association.

Stability of autoantibodies and their relation to genetic and metabolic markers of Type I diabetes in initially unaffected schoolchildren

AIMS/HYPOTHESIS

To study temporal changes in positivity for autoantibodies associated with Type I (insulin-dependent) diabetes mellitus and the relations between these antibodies, HLA-DQB1-risk markers and first-phase insulin response (FPIR) in non-diabetic schoolchildren.

METHODS

The stability of the antibody status over 2 years was assessed in 104 schoolchildren initially positive for islet cell antibodies (ICA) or antibodies to the 65,000 M(r) isoform of the glutamic acid decarboxylase (GADA) or both and in 104 antibody-negative control children matched for sex, age and place of residence. All children were also studied for their first-phase insulin response and HLA-DQB1 alleles on the second occasion.

RESULTS

On the second occasion 3 of the 98 initially ICA-positive children, 3/13 of those positive for antibodies to the IA-2 protein (IA-2A), 1/17 GADA-positive and 2/7 of those positive for insulin autoantibodies (IAA) tested negative for these antibodies. Children with IA-2A, GADA, IAA and multiple (> or = 2) antibodies had significantly lower first-phase insulin responses than the control children. In contrast, these responses did not differ between subjects with and without specific HLA-DQB1-risk alleles or genotypes. Of the six subjects with a considerably reduced first-phase insulin response three had multiple antibodies on both occasions but none of them had a DQB1 genotype conferring increased diabetes risk. Two subjects progressed to Type I diabetes within 3.4 years of follow-up, both of them having multiple antibodies and a considerably reduced first-phase insulin response but neither of them having a DQB1-risk genotype.

CONCLUSIONS/INTERPRETATION

Positivity for diabetes-associated autoantibodies is a relatively stable phenomenon in unaffected schoolchildren, although conversion to seronegativity can occur occasionally. Our observations also indicate that DQB1 alleles associated with decreased susceptibility to Type I diabetes do not protect from impaired beta-cell function or from progression to overt disease in initially unaffected schoolchildren.

Genetic markers, humoral autoimmunity, and prediction of type 1 diabetes in siblings of affected children. Childhood Diabetes in Finland Study Group

The relationships between genetic markers and disease-associated autoantibodies were studied in an unselected population of 701 siblings of children with type 1 diabetes, and the predictive characteristics of these markers over a period of 9 years were determined. Increased prevalences of all the antibodies were closely associated with HLA identity to the index case, the DR4 and DQB1*0302 alleles, and the DR3/4 phenotype and the DQB1*02/0302 genotype. Antibodies to GAD (GADA) were also associated with the DR3 and DQB1*02 alleles. Siblings carrying the protective DR2 and DQB1*0602-3 alleles were characterized by lower frequencies of islet cell antibodies (ICA), antibodies to IA-2 (IA-2A), and GADA. Higher levels of ICA were related to HLA identity, the DR4 and DQB1*0302 alleles, and the susceptible DQB1 genotypes, while no significant differences were observed in the levels of IA-2A, GADA, or insulin autoantibodies among siblings with different HLA risk markers. The DR2 or DQB1*0602-3 alleles were not related to the levels of any antibody specificity. A combination of the genetic markers and autoantibodies increased the positive predictive values of all autoantibodies substantially, which may have clinical implications when evaluating the risk of developing type 1 diabetes at the individual level or when recruiting high-risk individuals for intervention trials. However, because such combinations also resulted in reduced sensitivity, autoantibodies alone rather than in combination with genetic markers are recommended as the first-line screening in siblings. Finally, not all siblings with a broad humoral autoimmune response or high-risk genetic markers present with type 1 diabetes, while some with a low genetic risk and weak initial signs of humoral autoimmunity may progress to disease.

Diabetes-associated autoantibodies in relation to clinical characteristics and natural course in children with newly diagnosed type 1 diabetes. The Childhood Diabetes In Finland Study Group

We analyzed 747 children, younger than 15 yr of age, with newly diagnosed diabetes, for antibodies to glutamic acid decarboxylase (GADA), the IA-2 protein (IA-2A), insulin (IAA), and islet cells, to evaluate the influence of positivity for GADA, IA-2A, IAA, or multiple (> or = 3) autoantibodies at diagnosis, on the clinical presentation and natural course of the disease over the first 2 yr and to characterize autoantibody-negative patients. At diagnosis, 73.2% of the children tested positive for GADA, 85.7% for IA-2A, 54.2% for IAA, and 72.6% for multiple autoantibodies. Only 17 subjects (2.3%) had no detectable autoantibodies. The patients testing positive for multiple autoantibodies were younger than the remaining children (P < 0.001). A similar age difference was seen when comparing IAA-positive and -negative patients (P < 0.001). There was no significant difference between the GADA-positive and -negative subjects in the degree of metabolic decompensation at diagnosis, whereas those testing positive for IA-2A had reduced serum C-peptide concentrations (P = 0.003), and those positive for IAA had lower glycated hemoglobin values. The patients with no detectable autoantibodies had higher serum C-peptide levels (P = 0.007) at diagnosis than did the other subjects. The children initially positive for IA-2A had decreased serum C-peptide concentrations at 24 months (P = 0.045), and their daily insulin dose was higher at 18 (P = 0.005) and 24 months (P < 0.001). The patients who tested positive for multiple autoantibodies at diagnosis had decreased serum C-peptide levels (P < 0.001) and higher insulin doses (P = 0.005) at 12, 18, and 24 months. A lower proportion of them were also in clinical remission at 12 and 18 months (P = 0.01). Autoantibody-negative subjects needed less exogenous insulin at 6 and 18 (P = 0.01) and at 24 months (P < 0.001) than the other subjects, and a higher proportion of them were in clinical remission at 18 months (P < 0.001). We conclude that positivity for multiple diabetes-related autoantibodies is associated with accelerated beta-cell destruction and an increased requirement for exogenous insulin over the second year of clinical disease, indicating that multiple autoantibodies reflect an aggressive progression to total beta-cell destruction. Patients testing negative for diabetes-associated autoantibodies at diagnosis seem to have a milder degree of beta-cell destruction, but their metabolic decompensation is similar to that seen in other affected children, suggesting that they do represent classical type 1 diabetes.

Analysis of an interferon-gamma gene (IFNG) polymorphism in Danish and Finnish insulin-dependent diabetes mellitus (IDDM) patients and control subjects. Danish Study Group of Diabetes in Childhood

A CA-repeat polymorphism within the first intron of the interferon (IFN)-gamma gene was analyzed. This polymorphism was recently demonstrated to be associated with insulin-dependent diabetes mellitus (IDDM) in Japanese subjects. We typed 266 IDDM patients and 195 control subjects of Danish Caucasoid origin. No significant differences in allele or genotype frequencies between patients and control were observed. In addition, we typed 168 IDDM and 110 control subjects of Finnish origin. A significant disease association of the studied IFN-gamma allelic pattern was found (p = 0.029). Analysis of data according to HLA-DQB1 susceptibility status did not reveal heterogeneity of risk at the IFN-gamma locus in either of the populations. Fifty-five Danish and 94 Finnish IDDM multiplex families with at least two affected siblings (660 individuals) were typed to test for transmission disequilibrium (TDT). No evidence for overall transmission disequilibrium using either an allele-wise (p = 0.42; combined data) or a genotype-wise analysis (p = 0.21; combined data) could be detected. Thus, the modest significance level observed in the Finnish case-control study and the failure to replicate it by the TDT provide little support for the hypothesis that the IFN-gamma gene microsatellite is associated with IDDM.

HLA-DQB1-defined genetic susceptibility, beta cell autoimmunity, and metabolic characteristics in familial and nonfamilial insulin-dependent diabetes mellitus. Childhood Diabetes in Finland (DiMe) Study Group

Familial aggregation of insulin-dependent diabetes mellitus (IDDM) is a common phenomenon, but the reasons behind it are poorly understood. To investigate whether there is heterogeneity between familial and nonfamilial forms of IDDM we compared genetic, immunological, and clinical characteristics of diabetic children with and without an affected first-degree relative in a population-based series of Finnish children with IDDM. The frequencies of HLA-DQB1 genotypes known to be associated with high (DQB1*0302/0201) or moderate (*0302/x) IDDM risk in the Finnish population were increased, while the proportions of DQB1 genotypes associated with low or decreased risk for IDDM were reduced in the 121 familial cases as compared with the 574 nonfamilial cases (32.7 vs. 21.3%, 41.3 vs. 35.9%, 18.3 vs. 31.4%, and 7.7 vs. 11.4%, respectively; P = 0.002). The frequencies and serum concentrations of islet cell antibodies, insulin autoantibodies, and antibodies to the 65-kD isoform of glutamic acid decarboxylase were similar at diagnosis in the familial and nonfamilial cases. The 31 first-affected cases in the multiple case families were younger at diagnosis than the nonfamilial cases (6.9 vs. 8.5 yr; P < 0.05). The 90 second-affected familial cases had less severe metabolic decompensation at diagnosis than either the first-affected familial or nonfamilial cases. In conclusion, familial aggregation of IDDM in Finland is at least partly explained by a higher frequency of IDDM susceptibility genes in families with multiple affected individuals. The lack of differences in autoantibody levels between the familial and nonfamilial cases indicates homogeneity rather than heterogeneity in the pathogenetic process of beta cell destruction.

Effect of polymorphism in the insulin gene region on IDDM susceptibility and insulin secretion. The Childhood Diabetes in Finland (DiMe) Study Group

In addition to the major genetic determinants of insulin-dependent diabetes mellitus (IDDM) in the major histocompatibility complex (MHC) on chromosome 6, there are also minor genetic risk markers, e.g. in the insulin gene region on chromosome 11p15.5 (IDDM2). We studied the significance of the-23 HphI polymorphism in the insulin gene region (-23 HphI INS) in the Finnish population in combination with HLA genotyping data. The frequency of the-23 HphI INS +/+ genotype was higher in diabetic subjects with a low risk HLA DQB1 genotype than in control subjects (P = 0.05). Diabetic children in multiple-case families also had a higher frequency of the INS risk genotype than the controls (P < 0.05), and this difference was independent of the HLA genotype. Furthermore, we studied siblings positive for islet cell antibodies (ICAs) and/or insulin autoantibodies (IAAs) to evaluate the impact of the-23 HphI INS +/+ genotype on their beta-cell function assessed by sequential intravenous glucose tolerance tests and on their progression to IDDM. When analysing siblings with a low-risk HLA DQB1 genotype, those with the-23 HphI INS +/+ genotype had lower first phase insulin responses (P < 0.02) on several occasions than the remaining sibling. Six siblings (26.1%) in the former group progressed to clinical disease during the observation period, whereas none in the latter group presented with IDDM (P = 0.01). These observations suggest that the-23 HphI INS +/+ polymorphism is associated with an increased risk of IDDM in subjects without predisposing genes in the MHC region. The enhanced susceptibility may be related to a reduced insulin secretory capacity.

The immunoglobulin heavy-chain variable region in insulin-dependent diabetes mellitus: affected-sib-pair analysis and association studies

We have analyzed immunoglobulin heavy-chain variable-region (VH) polymorphisms and genetic susceptibility to insulin-dependent diabetes mellitus (IDDM) by using a set of polymorphic loci that span approximately 1,000 kb of the VH region on chromosome 14q32. One hundred one Finnish families with at least two children affected with IDDM were studied. Conventional RFLPs determined by hybridization were used, since no microsatellite repeat markers have been available for this gene region. No evidence for linkage between the VH genes and IDDM could be obtained from haplotype-sharing analysis among the 133 diabetic sib pairs. The frequencies of various VH genotypes were also compared between 101 familial IDDM cases and 114 controls derived from the Finnish background population. The distribution of the genotypes at the VH2-B5 locus was significantly different between these groups (P=.004), the 3.4/3.4 genotype being less common in the IDDM cases. In addition, a different genotype distribution at the VH5-B2 locus was observed in the diabetic subjects (P = .022). When the IDDM cases were stratified by presence or absence of the high-risk HLA-DQB1*0302 allele, no differences in VH genotype frequencies were observed between the 0302-positive and 0302-negative cases. In the transmission test for linkage disequilibrium (TDT), no differences were found between the expected and observed frequencies of the transmitted alleles at the VH2-B5 or VH5-B2 locus. In conclusion, significant differences in VH genotype distributions were observed between the familial IDDM cases and the controls, but the observed associations could not be confirmed by the TDT. Haplotype sharing analysis provided no evidence for genetic linkage between the VH gene region and IDDM.

Rapid HLA-DQB1 genotyping for four alleles in the assessment of risk for IDDM in the Finnish population. The Childhood Diabetes in Finland (DiMe) Study Group

OBJECTIVE

To study the effectiveness of MHC genotyping in the assessment of risk for IDDM based on the identification of alleles that are significantly associated with risk for IDDM (DQB1 *0302 and *0201) and protection from it (DQB1 *0602/*0603 and *0301).

RESEARCH DESIGN AND METHODS

A long series of 649 index cases of IDDM, together with their healthy siblings and 756 healthy blood donors, was collected in Finland. The samples were analyzed using a large-scale assay procedure that was developed for rapid screening purposes. The method utilizes time-resolved fluorometry to detect the hybridization of lanthanide-labeled allele-specific oligonucleotide probes with amplified gene product.

RESULTS

A total of 61.9% of IDDM index cases had high risk (DQB1 *0201/*0302) or moderate risk (DQB1 *0302/x [x meaning DQB1 *0302 or a nondefined allele]) genotypes compared with 14.3% of the reference population. In patients and control subjects, the frequencies of low risk genotypes were 28.0 and 22.1%, respectively, and those of decreased risk genotypes, 10.0 and 63.6%. The relative risk of a *0201/*0302 genotype was 53.5 (31.1-92.8) compared with the decreased risk genotypes (63.6% of controls). The graded risk estimation was equally efficient in assessing the risk of IDDM in siblings of child with IDDM.

CONCLUSION

The near-automatic typing procedure developed is attractive for large-scale screening projects, such as diabetes prevention and intervention trials.

Glutamic acid decarboxylase antibodies in relation to other autoantibodies and genetic risk markers in children with newly diagnosed insulin-dependent diabetes. Childhood Diabetes in Finland Study Group

To study the frequency of antibodies to glutamic acid decarboxylase (GAD65A) at the diagnosis of insulin-dependent diabetes mellitus (IDDM) and to evaluate the relation of these antibodies to other IDDM-associated autoantibodies and genetic risk markers of the disease, we analyzed 747 newly diagnosed diabetic children younger than 15 yr of age (mean, 8.4 yr) for GAD65A, islet cell antibodies, insulin autoantibodies, and human leukocyte antigen DR alleles. GAD65A were detected in 73.2% of the children, with a higher frequency in females than in males (77.1% vs. 70.1%; P = 0.04) and in index cases aged 10 yr or older than in younger children (79.0% vs. 68.7%; P = 0.004). The index cases positive for GAD65A had higher levels of islet cell antibodies (median, 40 vs. 34 Juvenile Diabetes Foundation units; P = 0.003) and insulin autoantibodies (median, 55 vs. 43 nU/mL; P = 0.03) than those testing negative for GAD65A. Human leukocyte antigen DR3/non-DR4 children had the highest GAD65A levels, whereas DR2-positive cases had levels of GAD65A similar to those found in other subjects. One third of the index cases (33.9%) tested positive for all three autoantibodies, 43.1% for two antibodies, and 18.2% for one antibody, whereas 4.8% were triple negative. The females had multiple antibodies (at least two antibodies) more often than the males (81.3% vs. 73.5%; P = 0.01). There was a significant trend for a higher frequency of multiple antibodies in young children (83.0% in those under 5 yr and 73.2% in those 10 yr or older; P = 0.02) and a higher frequency in DR3/4 heterozygous children than in those with DR3/non-DR4 (83.3% vs. 63.2%; P = 0.02). The results show that GAD65A antibodies are more frequent in girls and adolescents with newly diagnosed IDDM and suggest that DR3/non-DR4 subjects have increased GAD65A levels. Multiple antibodies in diabetic children are associated with young age, female sex, and DR3/4 heterozygosity.

Human leukocyte antigen identity and DQ risk alleles in autoantibody-positive siblings of children with IDDM are associated with reduced early insulin response. Childhood Diabetes in Finland (DiMe) Study Group

To investigate the relationship between human leukocyte antigen (HLA)-associated genetic factors and the development of beta-cell dysfunction, we performed sequential intravenous glucose tolerance tests (IVGTTs) on 81 islet cell antibody (ICA)-positive and/or insulin autoantibody-positive healthy siblings of children with newly diagnosed insulin-dependent diabetes mellitus (IDDM). A lower glucose disappearance rate (Kg) (P < 0.5) and decreased first-phase insulin response (FPIR) (P < 0.05) were observed on multiple occasions in HLA-identical siblings compared with the haploidentical or nonidentical ones. Siblings carrying the DQB1*0302/0201, -0302/x, or -0201/x genotype also had lower FPIRs (P < or = 0.05) at several time points than those with no DQB1 risk genotype. When all IVGTTs were taken into account, DQB1*0302/0201 heterozygous siblings had an abnormally low FPIR (< 45 mU/l; 3rd percentile) in at least one test more often than did siblings with no DQB1 risk genotype (50.0% vs. 6.1%; P = 0.001). Siblings carrying either the DQB1*0602 or the DQB1*0603 protective allele had lower serum peak ICA and glutamic acid decarboxylase (GAD)65 antibody levels (P = 0.023 and 0.007, respectively) and higher FPIRs on several occasions (P < 0.05) than those with the DQB1 risk genotypes. Progression to IDDM was related to both HLA identity and the presence of the DQB1*0302/0201 genotype. Normal Kg and FPIR levels were observed in siblings who were positive for only insulin autoantibody, and none of them developed IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)