Thyroid hemiagenesis in two sisters.

Two sisters with thyroid hemiagenesis are described. The patients presented diffuse thyroid enlargement of right lobe. The left lobe and isthmus were absent and thyroid scans were similar in both cases. The patients were clinically euthyroid. Basal serum thyroid hormones and TSH were within normal range, but TSH response to TRH administration was exaggerated in both patients. The finding of familial occurrence and the same functional and morphological characteristics of remnant thyroid tissue in both cases suggest a genetic determination for this abnormality.