[A study on anti-T3 and anti-T4 autoantibodies found in two sisters with juvenile hypothyroidism due to Hashimoto's thyroiditis (author's transl)].

Anti-thyroid hormone autoantibodies were found in two sisters of short stature (case 1: 13 years old, case 2: 10 years old). Physical examination revealed clinical findings of hypothyroidism with diffuse goiter. A diagnosis of Hashimoto's thyroiditis was made by open biopsy of the thyroid gland in both patients. Serum levels of T3 and T4 were assayed by double antibody radioimmunoassay. In case 1, serum T3 level was 16 ng/dl and serum T4 level was 2.0 microgram/dl. In case 2, serum T3 levels were high (range, 375 approximately 1660 ng/dl), while serum T4 remained at a very low level (0.9 microgram/dl). On the other hand, the level of T3 in case 2 as well as the level of T4 in case 1 was not detectable by a single antibody radioimmunoassay using dextran-coated charcoal or polyethylene glycol separation. In each case, the serum TSH level measured by double antibody radioimmunoassay was extremely high (255 microunits/ml in case 1, 240 microunits/ml in case 2), which was compatible with the clinical features of primary hypothyroidism. Sera from both patients were incubated with 125I-T3 and 125I-T4, followed by precipitation with polyethylene glycol. The binding of 125I-T3 with serum from case 2 and the binding of 125I-T4 with serum from case 1 were markedly high, suggesting the presence of T3- and T4-binding substance(s) in the sera. IgG prepared from the sera of both cases showed marked and specific binding with T3 in case 2 and T4 in case 1. The association constant for T4-antibody in case 1 was 5.2 x 10(8) M-1 and for T3-antibody in case 2 was 5.0 x 10(9) M-1. The binding capacity for T4 was 1.2 ng/ml.IgG and for T3 was 0.3 ng/mg.IgG.