Time clustering of high titre insulin autoantibodies (IAA) in the cord blood of infants born to non-diabetic mothers.
Insulin autoantibodies (IAA) are markers for autoimmune insulitis, and are reported in up to 100% of diabetic children before the age of five years, but in fewer than 1% of their controls. Their origins are unknown. In this report a cluster of high titre IAA in cord blood is reported, distinct from the low titre 'non-specific' binding previously described. The distributions of displaceable insulin binding measured in adults (Group A, n = 79), adolescents (Group B, n = 19), primary school children (Group C, n = 32) and third trimester pregnant women (Group D, n = 60) were all unimodal, normal and not different from each other (A = 0.57+/-0.64%, B = 0.87+/-0.45%, C = 0.81+/-0.87% and D = 0.35+/-0.48%). The distribution of insulin binding in the cord sera of consecutive newborns (n = 428) born between October and the following May, however, was bimodal. The first distribution, included 400 sera, was symmetrical and not different (0.79+/-0.45%) from groups A, B, C and D. The second distribution comprised the remaining 28 sera (7% of the total sample) with insulin-displaceable binding values in an IDW-validated radio assay ranging from 2.2% to 31.1%. The appearance of IAA was not HLA-restricted, but the frequency of IAA+ samples was seen to vary over five consecutive months. The timing is consistent with acute viral infection, but the implications for future insulin dependent diabetes will await long-term follow-up of the children and mothers involved.