[Susceptibility to chronic HLA-system-associated lymphocytic thyroiditis. Its relationship with insulin-dependent diabetes mellitus].

The genetic association between HLA-system and chronic lymphocytic thyroiditis (CLT) related or not to type I diabetes mellitus (IDDM), have been analysed in three groups of children: 16 with CLT, 9 with CLT and IDDM, 11 with IDDM and 200 normal controls. The DQw1 antigen (75% vs 55%) was found associated with CLT, furthermore the observed increase of DR1 and DR2 antigens (37% respectively) is secondary to the linkage disequilibrium that exists between them and DQw1. DR3 antigen (60%) was found significantly increased (p less than 0.001) in CLT patients compared with the control group (24%). In diabetic patients, DR3 and DR4 were found in 85% and 63% respectively (p less than 0.001). The DR3 associated haplotype in CLT patients was different from the diabetic one's. All the diabetics, but one, were DR3-B18 haplotype carriers, but this association was only found in 25% CLT patients. The titre of thyroid microsomal antibodies (MCHA) was more frequent in the patients with DQw1 antigen (MCHA DQw1+ : 1/1072; DQw1- : 1/606). The CLT predisposition in childhood may be influenced by genes located within the HLA-region probably more than one, different from the genes related to IDDM. One of this genes closed to the HLA-DQ region, will be involved in the production of autoantibodies.