Distribution and inheritance of low serum thyroxine-binding globulin levels in Australian Aborigines: a new genetic variation

Evidence is presented that low serum thyroxine-binding globulin (TBG) levels in Aborigines are widely distributed throughout Australia, and that these are inherited rather than acquired. Levels of TBG in children, and lack of any correlation of low TBG levels with alcohol consumption or liver dysfunction, suggest that the low levels are not acquired in adult life. Genetic studies in eight families indicate (with one exception) an autosomal dominant pattern of inheritance with direct male-to-male transmission. These findings are in marked contrast to the much rarer X-linked pattern of inheritance of low TBG levels in Caucasians. This type of prevalent and inherited low level of TBG in serum appears so far to be unique to the Aboriginal race. The synthesis (or degradation) of TBG may be controlled by an autosomal gene in Aborigines.