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 ins ulin-dependent diabetes mellitus (IDDM), are detected in similar to 85 % of children with recently diagnosed diabetes. Because the ICA assay is semiquantitative and difficult to standardize, alternative assays a re needed. When glutamic acid decarboxylase 65 (GAD 65) was discovered as a major islet antigen, the measurement of antibodies to GAD 65 (GA DA) was considered a good alternative to ICA. Recently, however, we sh owed 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 (u sing radioligand binding assays for IA2-ab and GADA) in 100 recently d iagnosed 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 o nly GADA. Thus, 6 of the 100 patients had neither ICA, IA2-ab, nor GAD A. Combining the IA2-ab and GADA assays gave positive results for auto immunity 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 effect ive alternative to the ICA assay.