In a family with X-chromosome-linked inheritance of thyroxine (T
4)-binding globulin (TBG) deficiency, serum free T
4 values were low in three of four members, but free triiodothyronine (T
3) values were normal in all four of them. Binding capacities of T
4-binding prealbumin (TBPA) were high in three of four members. In the propositus, a 47-year-old male, whose T
4-binding capacity of TBG was null, half-time of serum T
4 was shortened, turnover rate, distribution space and clearance rate all increased, extrathyroidal organic iodine pool decreased and degradation rate of T
4 was unchanged compared with normal values. While half-time of his serum T
3 was prolonged, turnover rate, extrathyroidal pool and degradation rate of T
3 decreased, and T
3 distribution space and clearance rate increased compared with normal values. When 0.24mg of ethinylestradiol-3-methylester was administered daily by mouth to the propositus for 1 month, halftime of serum T
4 was prolonged, total T
4 increased and T
4-binding capacity of TBPA decreased but free T
4, T
4-binding capacity of TBG and the degradation rate of T
4 were unchanged. Meanwhile half-time of his serum T
3 was shortened, total and free T
3 levels and degradation rate of T
3 increased.
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