Islet autoimmunity in infants with a Type I diabetic relative is common but is frequently restricted to one autoantibody

AIMS/HYPOTHESIS

To determine the sequence of development of islet autoantibodies and their relation to HLA genes in infants at risk for Type I diabetes followed from birth.

METHODS

We followed 357 (189 male, 168 female) infants, with a first degree relative with Type I diabetes for a mean of 3 years from birth. Human leukocyte antigen typing and assays for insulin autoantibodies (IAA), glutamic acid decarboxylase antibodies (GADAb) and tyrosine phosphatase IA2 (IA2Ab) antibodies were done on cord blood, and venous blood was sampled every 6 months for IAA, GADAb and IA2Ab.

RESULTS

We did not find any antibodies in 263 (73%) infants; 50 (14%) were positive for a single antibody once, 19 (5%) for a single antibody more than once and 25 (7%) for two or more antibodies. Of the latter, 10 (2.8% overall) were persistently positive; they had higher frequencies of HLA DR4 (p < 0.01) and HLA DR3, 4 (p < 0.05). Of the group persistently positive for two or more antibodies four infants developed diabetes. Insulin autoantibodies were the first ones to develop in 64% of infants with two or more antibodies.

CONCLUSION/INTERPRETATION

Infants with high risk HLA-DR alleles and multiple antibodies at high risk for diabetes were identified. A much larger group of infants had transient low level increases usually of a single antibody. Whereas transient low level positivity could be attributed to difficulties with assay technique and cut off levels for normality, the results overall support the phenomenon of transient 'self limited' islet autoimmunity in at risk infants.

Antibodies to the protein tyrosine phosphatases IAR and IA-2 are associated with progression to insulin-dependent diabetes (IDDM) in first-degree relatives at-risk for IDDM

Insulin-dependent diabetes mellitus (IDDM) is preceded by the presence of antibodies against islet proteins including a protein tyrosine phosphatase (PTP) designated IA-2. Recently, we cloned a novel PTP named IAR which shares 43% sequence identity with IA-2 and is recognised by antibodies from a majority of patients with IDDM. The aim of the present study was to determine whether IAR antibodies (IAR Ab) or IA-2 antibodies (IA-2 Ab) are associated with progression to IDDM in first-degree relatives "at-risk" for IDDM (operationally defined as those with islet cell antibodies [ICA] > or = 20JDFU or insulin autoantibodies [IAA] > or = 100 nU/ml), and to examine combinations of IAR Ab and IA-2 Ab in these subjects. The sensitivity and specificity of these antibodies were also examined in patients with recent-onset IDDM. Using Cox's Proportional Hazards Model, the number of siblings with IDDM was associated with progression to IDDM in "at-risk" relatives, but other covariables (age, sex, number of affected offspring or parents) were not significantly associated. Using number of affected siblings as a covariable, both IAR and IA-2 antibodies were significantly associated with progression to IDDM (p < 0.005). Combinations of both antibodies, however, did not result in a significantly stronger association with progression to IDDM. The threshold of positivity for IAR Ab (0.5 units) and IA-2 Ab (3.0 units) assays was adjusted to give the same specificity (97.9%) for each assay in 144 healthy control subjects, to allow standardised comparisons. Levels of IAR Ab and IA-2 Ab were strongly correlated in 53 recent-onset IDDM patients (r = 0.70, p < 0.0001) but 11.3% had IAR Ab in the absence of IA-2 Ab and 16.9% had IA-2 Ab in the absence of IAR Ab. The sensitivity for IDDM (defined as the proportion of IDDM patients positive) was 56.6% for IAR Ab and 62.3% for IA-2 Ab. We conclude that there is considerable overlap in IA-2 Ab and IAR Ab positivity, although either antibody can occur independently in IDDM patients. Both IAR Ab and IA-2 antibodies are associated with progression to IDDM in first-degree relatives at-risk of IDDM, but the use of IAR and IA-2 antibodies in combination are not significantly more strongly associated with progression than single antibodies. IAR Ab may play an important role in the prediction of IDDM.