Islet cell antibodies (ICA), insulin autoantibodies (IAA), islet cell surface antibodies (ICSA) and C-peptide in 1031 school children in a population with a high background incidence of IDDM

Prevalence of interrelated autoantibodies in thyroid diseases and autoimmune disorders

OBJECTIVE

We determined the autoantibody profile in autoimmune thyroid diseases (AITD) and examined the distribution of thyroid-related autoantibodies in other autoimmune disorders.

METHODS

We tested sera from 234 patients with Graves' disease (GD), 130 with Hashimoto's thyroiditis (HT), 249 with other autoimmune diseases, and 50 healthy controls by enzyme-linked immunosorbent assay or radioimmunoassay.

RESULTS

Autoantibodies except TSH receptor antibody (Ab), anti-thyroglobulin (Tg) Ab and anti-thyroid peroxidase (TPO) Ab were not significantly prevalent in patients with AITD despite a significantly high elevation of thyroid-related Ab. Significant prevalence of autoantibodies related to AITD was observed in type 1 diabetes patients. Elevation of anti-Tg Ab was seen in patients with primary biliary cirrhosis (PBC) and autoimmune hepatitis (AIH), and anti-TPO Ab was elevated in patients with PBC. Although the prevalence of anti-acetylcholine receptor Ab and systemic lupus erythematosus (SLE)- related Ab was significant in AIH, primary Sjögren's syndrome (pSS)-related Ab were also found in both liver diseases. In myasthenia gravis (MG) patients, thyroid-related Ab and pSS-related Ab were detected in both MG groups, although SLE-related Ab were limited to the anti-muscle specific kinase Ab-positive MG patients. In patients with connective tissue diseases, anti- Tg Ab and anti-TPO Ab were significantly prevalent.

CONCLUSION

Thyroid-related Ab were significantly elevated in all autoimmune diseases. Conversely, the elevations of Ab were not significant in the patients with AITD, suggesting a close relationship between AITD and other immune-mediated diseases.

Seasonal variation in the diagnosis of type 1 diabetes in south-east Sweden

With the aim to survey the seasonal pattern of diagnosis of type 1 diabetes we included all 1903 children <16 years of age and who had been diagnosed with type 1 diabetes between 1977 and 2001 in the south-east of Sweden. To investigate the seasonal pattern a mixture of two cosine functions was included in a logistic regression model. There was a clear seasonal variation over the years (p<0.001). Children in the oldest age group (11-15 years) showed the most obvious seasonal variation (p<0.001). Children with a short duration of symptoms had about the same seasonal variation as children with a long duration. Both children with and without an infection 3 months prior to diagnosis showed significant seasonal variation (p<0.001) although the seasonal pattern differed between the two groups (p<0.001). As the incidence of diabetes increased during the 25 years the study period was divided into periods of 5 years and it was only during the two last periods that significant seasonal variation occurred. There is a clear seasonal variation in diagnosis of type 1 diagnosis in children and the results suggest that children with a less aggressive disease process at diagnosis were most responsible for this variation. Children with and without prior infection showed a different seasonal pattern.

Insulin autoantibodies are of less value compared with islet antibodies in the clinical diagnosis of autoimmune type 1 diabetes in children older than 3 yr of age

BACKGROUND

Insulin autoantibodies (IAA), antibodies against endogenous insulin, may be detected in type 1 diabetic children before the start of insulin treatment.

OBJECTIVE

To relate IAA to islet antibodies (i.e., islet cell antibodies [ICA], and antibodies against two ICA-related islet antigens, glutamic acid decarboxylase 65 [GADA] and protein tyrosine phosphatase IA-2 [IA-2 A]) at diagnosis, and to endogenous beta-cell function at follow-up after diagnosis in diabetic children.

SUBJECTS

We investigated 74 children, aged 1-15 yr, at the diagnosis of diabetes and 1-10 yr later. Insulin treatment may induce antibody development against exogenous insulin. Patients with insulin treatment > or = 1 wk (n = 5) were therefore excluded from the final analysis.

METHODS

Radioligand-binding assays based on human recombinant antigen were used to measure IAA, GADA, and IA-2 A. ICA were determined with indirect immunofluorescence.

RESULTS

IAA were detected at a significantly lower frequency (43%; p < or = 0.001) than ICA (86%), GADA (72%), and IA-2 A (80%). In agreement, IAA measurements only marginally increased the frequency of positive autoimmune markers at diagnosis of diabetes (from 97 to 99% positive for at least one autoantibody). Preserved beta-cell function (detectable fasting p-C-peptide levels) was found in only nine patients, who were older (13 +/- 3 vs. 7 +/- 6 yr, p = 0.002) and had fewer of the antibodies (IAA, GADA, IA-2 A, ICA) in high titer (> median) compared with 60 patients with undetectable p-C-peptide levels.

CONCLUSIONS

Insulin autoantibodies are of less clinical value compared with islet antibodies in the diagnosis of autoimmune type 1 diabetes in children.

Islet autoantibodies in the prediction of diabetes in school children

In 1987 serum was collected from 1031 non-diabetic schoolchildren in the Southeast area of Sweden with the aim of evaluating islet autoantibody status (ICA, GADA and IA2-ab) in the prediction of diabetes in schoolchildren. The clinical development of Type 1 diabetes in the children was assessed in 1994 and 1997. The combination of ICA, GADA and IA2-ab were found in four subjects whereas six had two and 35 children one of these antibodies. After 10 years, six of the 1031 children had developed clinical diabetes and five of these six children were positive for islet antibodies. Two were positive for all three antibodies, two were positive for ICA and GADA, and one was positive for GADA. Among the individual autoantibodies, ICA showed the highest positive predictive value (29%) whereas the predictive value for the combination of two autoantibodies was highest for GADA and ICA (40%). Thus, GADA and ICA measurements may be a rational approach to detect schoolchildren at risk for developing diabetes.

Protein tyrosine phosphatase-like protein IA2-antibodies plus glutamic acid decarboxylase 65 antibodies (GADA) indicates autoimmunity as frequently as islet cell antibodies assay in children with recently diagnosed diabetes mellitus

Islet cell antibodies (ICA), the classical autoimmunity marker for insulin-dependent diabetes mellitus (IDDM), are detected in ∼85% of children with recently diagnosed diabetes. Because the ICA assay is semiquantitative and difficult to standardize, alternative assays are needed. When glutamic acid decarboxylase 65 (GAD 65) was discovered as a major islet antigen, the measurement of antibodies to GAD 65 (GADA) was considered a good alternative to ICA. Recently, however, we showed that 1 in 3 ICA-positive diabetic patients do not have GADA. Now, antibodies against the protein tyrosine phosphatase-like protein IA2 (IA2-ab) have been detected in IDDM. To find out whether measurements of IA2-ab combined with those of GADA could detect autoimmunity to the same extent as ICA, we have measured all three kinds of antibodies (using radioligand binding assays for IA2-ab and GADA) in 100 recently diagnosed diabetic and 100 control children: ICA were found in 87, IA2-ab in 69, and GADA in 66 of the 100 diabetic patients, whereas in the 100 control children ICA were found in 2, IA2-ab in 1, and GADA in 3. Among the 87 ICA-positive patients, 45 (52%) had both IA2-ab and GADA, 21 (24%) had only IA2-ab, and 16 (18%) had only GADA, whereas 5 (6%) lacked both IA2-ab and GADA. Among the 13 ICA-negative patients, 1 (8%) had both IA2-ab and GADA, 2 (15%) had only IA2-ab, and 4 (31%) had only GADA. Thus, 6 of the 100 patients had neither ICA, IA2-ab, nor GADA. Combining the IA2-ab and GADA assays gave positive results for autoimmunity in 89 of the 100 patients, compared with 87 by the ICA assay. The combination of the IA2-ab and GADA assays appears to be an effective alternative to the ICA assay.

Antibody screening in a population of children

The first large-scale (secondary) intervention trials have been initiated in first-degree family members of patients with insulin-dependent diabetes mellitus (IDDM). Within a few years, data from these studies may suggest that intervention is possible, thereby opening similar approaches in the general population. However, before large-scale intervention studies can be initiated, several problems need to be solved. One of these problems is the lack of knowledge on the natural course of beta-cell autoimmunity. This review analyses this and other issues related to population-based prediction for IDDM. At present, no long-term follow-up studies are available in large-sized populations, but data show that prediction in the general population is both technically feasible and likely to have sufficient power to be useful in prevention trials. More data need to be generated, not only to determine which markers are most likely to give good prediction but also to obtain knowledge on the natural course, psychosocial impact and cost-effectiveness of screening.

Measurement of antibodies against glutamic acid decarboxylase 65 (GADA): two new 125I assays compared with [35S]GAD 65-ligand binding assay

Recently, 65-kDa glutamic acid decarboxylase (GAD 65) antibodies (GADA) have been introduced as autoimmune markers in blood to confirm the diagnosis of insulin-dependent diabetes mellitus (IDDM). In this study, to evaluate two new assays that use 125I-labeled GAD 65, we assayed samples from 100 children with recent onset of diabetes and 100 control children; the results were compared with those of a [35S]GADA assay and with results for islet cell antibodies (ICA), the conventional autoimmune marker. Receiver operating characteristic (ROC) curve analysis showed one of the new assays (from RSR) to be more sensitive (P = 0.01) than the comparison ([35S]GADA) assay, whereas the second new assay (from Elias) was less sensitive (P &lt;0.001). The GADA frequency at 97.5% specificity was greatest in the comparison assay: 63 of 100 vs 41 of 100 (P &lt; 0.01) and 53 of 100 (P = 0.16) in the RSR and Elias assays, respectively. Almost all GADA-positive patients had ICA, but one-third of the ICA-positive patients was GADA-negative. Accordingly, adding GADA analysis results to ICA testing increased the frequency of detection of autoimmune markers only slightly (from 81% to 85%). In conclusion, at 97.5% specificity the [35S]GADA assay seemed to be more efficient than the 125I assays, although the difference was significant only for the Elias 125I assay. Antigen-specific antibodies other than GADA may explain the difference in GADA and ICA frequencies.