X-chromosome linked inheritance of decreased thyroxine-binding globulin.

Partial thyroxine-binding globulin (TBG) deficiency was observed in a euthyroid boy. A family study was conducted in order to trace the defect. Of the 15 members, 3 male subjects were found to be affected, whereas 6 female subjects were shown to be carriers of the trait. The inheritance pattern of the partial TBG deficiency was found to meet the criteria for X chromosome linked transmission. No association with other X-linked characters (colour blindness, glucose-6-phosphate dehydrogenase activity) was present. Karyotype analysis in the female subjects did not show any abnormality. TBG deficiency does not impair thyroid function. No difference was noted in free thyroxine levels in normal and affected subjects.