Another form of the hereditary persistence of fetal hemoglobin (the Atlanta type)?

The propositus in a Black family has elevated Hb-F and approximately equal amounts of Hb-A and Hb-S. Hematological and chemical studies of the propositus and his family show elevated Hb-F in the father and a sibling and sickle cell trait in the mother and another sibling. This family is believed to have a form of the hereditary persistence of fetal hemoglobin in which beta chains are produced in cis to the determinant.