The JAL antigen was found to have an overall frequency of 0.004% in the Swiss population and 0.06% in French-speaking Swiss. Family studies of 5 JAL+ individuals have shown that the JAL antigen is not part of the ABO, MNSs, Fy, Jk and Co blood group systems, or the Se system, nor is it X- or Y-linked. JAL is encoded by the RH locus or by a very closely linked locus. The number RH48 (4.48) has been assigned for JAL by the International Society of Blood Transfusion Working Party on Terminology for Red Cell Surface Antigens.

A multilaboratory investigation during several years has identified a low incidence antigen JAL on the red cells of 7 propositi. JAL appears to be associated with two unusual Rh complexes, one of which produces a depressed C antigen and the other a depressed c antigen. Family studies strongly suggest that the JAL antigen is encoded by the RH locus. Anti-JAL has been implicated in haemolytic disease of the newborn and is thus considered to be a clinically significant antibody.