Inheritance of the Diego (Dia) blood-group factor.

THE DIEGO BLOOD-GROUP FACTOR (Dia) was discovered in 1953 (Levine and Robinson 1957) and has been studied fairly extensively in the subsequent four years by Arends and Layrisse (1956), Levine, Robinson, Layrisse, Arends, and Sisco (1956), Lewis, Chown, and Kaita (1956), and Junqueira, Wishart, Ottensooser, Pasqualin, Fernandez, and Kalmus (1956). It has a very low frequency in Caucasians and quite a high frequency in American Indians. It is fairly common in those Japanese and Chinese who have been tested, but was not found among a group of 156 Eski-mos. Levine et al. (1956, 1957) showed that Dia is not identical with the other known factors of low incidence (except that Levay was not compared). It was suggested that Dia is not related to the nine established blood group systems but belongs to a tenth independent blood group system. The evidence for genetic independence of Dia that has been presented up to the present time, however, is not as complete as one would like. Levine and Robinson (1957) did extensive blood grouping tests in one family in which the factor Dia occurs, but showed only its probable independence from the Rh and MINS blood groups. They also had suggestive evidence that Dia and Jk" are at least not closely related. Since the antibody anti-Dia reacts only by the indirect Coombs method, it is tempting to think that Dia may belong in the Kell, Duffy, or Kidd blood group systems, since it is the antibodies of these systems that characteristically react only by the Coombs method. In 1956 the blood groups of some Quechua Indians in an isolated community of the Peruvian Sierra were tested (Allen Newman, Of 308 tested with anti-Dia*, 74 (24 per cent) were positive, indicating that the gene frequency of Dia in that population is about 13 per cent. Because the study of the Diego factor was one of the more important aims of the expedition, families were obtained when possible and testing was as complete as possible in the families