Islet cell antibodies are less predictive of IDDM among unaffected children in the general population than in sibs of children with diabetes. The Childhood Diabetes in Finland Study Group.
OBJECTIVE
To examine the controversial issue of whether islet cell antibodies (ICAs) have a higher predictive value for progression to clinical IDDM in first-degree relatives of patients with diabetes than in the general population.


METHODS
ICAs were analyzed with standard immunofluorescence in two population-based groups: 765 sibs of children with recent-onset diabetes and 1,212 unaffected Finnish children <20 years of age at initial screening. Those positive for ICAs were additionally tested for antibodies to GAD (GADAs) and the protein tyrosine phosphatase-related IA-2 antigen (IA-2As). Subsequently, these subjects were observed for the manifestation of clinical IDDM over the next 7 years.


RESULTS
The frequency of both detectable ICAs and ICA levels > or =20 Juvenile Diabetes Foundation units (JDF U) was significantly higher among the sibs than in the general population (7.8 vs. 4.1% and 4.8 vs. 2.0%, respectively; P < 0.001). The prevalence of GADAs (37/60 vs. 3/48; P < 0.001) and IA-2As (31/60 vs. 0/48; P < 0.001) was increased among ICA-positive sibs compared with ICA-positive individuals from the background population. Over the next 7 years, 24 sibs (3.1%) and 3 unrelated children positive for ICAs (0.3%) progressed to clinical diabetes. The positive predictive value of ICAs was thus 6% in the general population and 40% among the sibs (P < 0.001), or 13 and 59%, respectively (P < 0.001), with an antibody cutoff level of 20 JDF U. The positive predictive value was related to the number of positive autoantibodies in sibs, which was 57% in those with three antibodies, 50% in those with two antibodies, and only 6% in those with ICAs alone.


CONCLUSIONS
These data show that the frequency of multiple autoantibodies is substantially lower in ICA-positive children representing the general population than in ICA-positive sibs of children with IDDM. As a consequence, the predictive value of ICAs for IDDM is higher in sibs of affected children than in the general population. This finding must be taken into account when planning intervention trials aimed at preventing or delaying the manifestation of clinical diabetes in individuals from the general population who test positive for ICAs.
Knip
M
M
Medical School and the Department of Pediatrics, Tampere University Hospital, University of Tampere, Finland. llmikn@uta.fi
Karjalainen
J
J
Akerblom
H K
HK
D000293:Adolescent; D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology* / Q000235:genetics* / Q000276:immunology; D005387:Finland / Q000453:epidemiology; D005455:Fluorescent Antibody Technique; D005500:Follow-Up Studies; D005968:Glutamate Decarboxylase / Q000276:immunology; D006801:Humans; D007223:Infant; D007515:Islets of Langerhans / Q000276:immunology; D008137:Longitudinal Studies; D008565:Membrane Proteins / Q000276:immunology; D009679:Nuclear Family; D011237:Predictive Value of Tests; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases / Q000276:immunology; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D018570:Risk Assessment; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013997:Time Factors
D001323:Autoantibodies; D001324:Autoantigens; D008565:Membrane Proteins; C024211:islet cell antibody; C516862:PTPRN protein, human; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D005968:Glutamate Decarboxylase