There are three antigens within the Scianna blood group system recognized by the International Society of Blood Transfusion (ISBT) Working Party on Terminology for Red Cell Surface Antigens. The first is Sc1, a high frequency antigen found in greater than 99 % of most populations. This antigen was originally described by Schmidt et al. in 1962 and named Sm. Second is Sc2, described by Anderson et al. in 1963 and named Bua. Lewis et al. reported the original Sm- cells were Bu(a+) and suggested they be renamed Sc1 and Sc2 following conformation that they were the products of alleles. The frequency of Sc2 is about 1% of Northern Europeans but the frequency is much lower in other populations. The incidence of Sc:1,2 is more common in Mennonites, as a selected population. The third antigen is Sc3, a high frequency antigen found on all cells except the extremely rare individuals that type Sc:-1,-2. Reported by McCreary in 1973, it was found while working with a sample of a patient from the Marshall Islands.
The Scianna antigens are encoded by a gene whose chromosomal location is on the short arm of chromosome 1 between 1p36.2-p22.1. The antigens are located on a glycoprotein containing disulfide bonds and an N-glycan, known as the Scianna glycoprotein (function unknown). To date, the antigens have only been found on erythroid cell lines. Individuals of the rare Sc:-1,-2 phenotype (the null phenotype ) do not appear to have any associated red cell membrane defect or anemia. The Sc:-1,-2 phenotype has been found most frequently (when found at all) amongst individuals native of the South Pacific Islands.
The antibodies against the Scianna antigens have been associated with mild to delayed transfusion reactions and mild hemolytic disease of the newborn. It is suspected that the Scianna blood group system could become as complex as some of the other blood groups. Some unique antibodies have been found that hint of an association with Scianna but lack the complete research necessary to qualify for blood group assignment. An example of possible expansion is the report of three Sc:1,-2 individuals that produced allo-antibodies that failed to react with Sc:-1,-2 red blood cells, and the antibodies were mutually incompatible. This is suggestive that there may be three more high incidence antigens within this system. In addition, the low incidence antigen Radin, may be a part of the Scianna system but is not an allele of Sc1 and Sc2.