544 FAMILIAL ATHYREOTIC HYPOTHYROIDISM IN TWO SIBLINGS

Abstract

Familial athyreosis is a cause of hypothyroidism seen much less frequently than sporadic athyreosis or cryptothyroidism. The present report concerns a brother and sister, now age 22 and 14 years respectively, who appear to have little or no functioning thyroid tissue. In both patients diagnosis was made and treatment begun in early infancy. There are 3 other normal siblings, and there is no family history of thyroid disease. The boy was first seen at age 13 years, exhibiting short stature, retarded bone age, mental retardation and other signs of hypothyroidism. Thyroid scan with 100 μCi of 131I revealed no detectable uptake. Under treatment with 60 mg desiccated thyroid/day TSH was 4.7 μU/ml, T4 4.7 μg/dl and T3 162 ng/dl (N 110-230). In the girl treatment had been stopped 4 years before we first saw her at age 9 years. She was below the 3rd percentile in height, was mentally retarded and exhibited the Kocher-Debré-Sémélaigne pseudohypertrophy of muscles. Bone age was 4½ years. T4 by CPB was 1.3 μg/dl (N=3-7) and TSH 54 μU/ml (N<10). Thyroid scans using 5 μCi of 131I and later with 2.5 mCi of Tc-99m failed to demonstrate any evidence for functional thyroid tissue. Parietal cell autoantibody titer in serum was not elevated. It has been suggested that Tc-99m provides a more critical evaluation of athyreosis than does 131I. Unlike the syndrome of familial athyreosis with thyrotropin deficiency (Miyai et al., NEJM 285:1043, 1971), in the present syndrome thyrotropin feedback appears to be normal.