A new polymorphism of thyroxin-binding globulin in three African groups (Mali) with endemic nodular goitre.

The thyroxin-binding globulin (TBG) polymorphism was investigated in three African groups: two belonged to the Bwa villages of Mali, and the third was a Dogon group living in the same area. The Bwa groups were characterized by the occurrence of nodular goitres, whereas the Dogon population did not show similar pathological symptoms. Females were more affected by goitre than males in the affected villages. The TBG polymorphism enabled us to demonstrate the presence of an undescribed allele (TBG C1) in these populations. The frequency of the TBG S allele was also higher than previously published in other African groups. We observed a disequilibrium in the distribution of the C and S alleles in the population, with an excess of homozygous TBG S individuals. No clear relationship between the TBG polymorphism and the number of nodules can be drawn.