The silent carrier of beta thalassemia: interaction with the typical beta thalassemic trait.

The case of a girl affected by a Colley's disease of moderate severity is reported. A brother and a sister had levels of Hb F respectively of 18% and 45%. The father showed all the hematological signs of heterozygous thalassemia. The mother, however, was normal so far as osmotic fragility, red cell morphology, and Hb A2 level are concerned. In vitro hemoglobin chains biosynthesis was performed in all the subjects. Both the parents showed an alfa/non alfa ratio typical of beta thalassemia. Therefore, the mother has to be considered a "silent" carrier of the trait. The daughters and the son have a less severe Colley disease originating by such a double heterozygosity.