Familial Thyroxine-Binding Globulin Deficiency in a Patient with Turner's Syndrome (XO)

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Abstract
A kindred with deficiency of thyroxine-binding globulin (TBG) is presented in which the propositus also has XO Turner's syndrome. The pattern of inheritance supports previous reports that TBG activity is X-chromosome linked. This genetic anomaly appears to be specific for TBG since no alterations in other hormone-binding proteins could be demonstrated. No inhibitor of thyroxine (T4) binding to TBG could be demonstrated. The presence of approximately half the normal maximal T4-binding capacity of TBG in heterozygous females is compatible with Lyon's hypothesis of random and permanent inactivation of one X chromosome during early fetal development of female somatic cells. There is no evidence of peripheral tissue thyroxine deficiency despite an absence of binding of T4 to the TBG zone and low total circulating T4. Daily hormonal utilization is normal. TBG deficiency in Turner's syndrome has not previously been described. The abnormality of TBG binding permitted identification of the maternal origin of the single X chromosome in the propositus.
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