*These numbers are just to help more easily identify each genes and are not the actual HPA System Numbers.
Similar to RBC Blood Group antigen the Human Platelet Antigen (HPAs) are each defined by antigen specific alloantibody sera.
However, unlike the RBC Blood Groups Systems, the HPA Systems were not named on a per gene or related gene basis with one or more antigens in each system.
Rather, one HPA gene can contain multiple HPA systems so in reality each biallelic antithetical antigen pair is really its own system.
For example, the HPA-1 system contains the antithetical antigens HPA-1a and HPA-1b, but this same gene also contains the HPA-4 system (HPA-4a and HPA-4b).
A 'w' after an HPA name indicates that no alloantibody has ever been found directed against this antigen's antithetical pair.
All of our HPA amino acid changes are in reference to the full length protein. There might be some difference in positions to other sources which list these amino acid changes in reference to positions in cleaved mature proteins.
For more information about HPA terminology and official allele lists please visit the following external link: IPD-HPA Database