The first Yt (also known as Cartwright) blood group system antigen, ie. Yta,
was described 1956 by Eaton et al. This blood group antigen was proven to be inherited as
a dominant character and independent from the other know systems at that time. In 1964,
Giles and Metaxas reported the first example of an antibody that detected the product of
the expected antithetical allele, Ytb. This latter discovery
raised the stature of the Yt system, which then became a chromosome marker of about the
same potential usefulness as the Lutheran system.
The two antigens of the Yt system, Yta and Ytb,
are both expressed at birth, however in a slightly lower expression level than seen on
adult cells. They were shown to be resistant to trypsin treatment, but sensitive to other
protein cleaving enzymes. Antibodies to these antigens were implicated in cases of delayed
transfusion reactions but were not reported to have caused hemolytic disease of the
newborn. No examples of Yt(a-b-) individuals have been found despite numerous studies.
From population studies, Ytb appeared to be lacking, or of very
low incidence, from Orientals, Amer-Indians and southern Africans; Yta
was found lacking in approximately one per thousand individuals of European origin.
This system remained unexciting until it was found that both of these antigens were
weak or absent from paroxysmal nocturnal hemoglobinuria (PNH) III red blood cells. With a
rush of activity in the early 1990's, it was found that the Yt blood group system
antigens represented amino acid substitutions on the GPI-linked glycoprotein,
acetylcholinesterase (AchE). This protein probably exists as a dimer (pair) in the red
cell membrane. Yta and Ytb are equated
to substitutions of a hisitidine and asparagine, respectively, at amino acid position 322
on the GPI-linked glycoprotein. AChE has been assigned a chromosome location at 7q22.
As of this date, there have been only two antigens associated with this system. Based
on the present knowledge of the placement on AChE, it is far more likely that any new
variants will be found investigating AChE peculiarities and their immune response than by
standard serological methods.