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.