Two previously proposed P1/P2-differentiating and nine novel polymorphisms at the A4GALT (P k ) locus do not correlate with the presence of the P1 blood group antigen

Table 1 The P/GLOB blood groups.

Phenotype	Frequency	Antigen present on RBC	Antibodies in serum
P₁	20–90%^a	P1, P^k, P	none
P₂	10–80%^a	P^k, P	Anti-P1
p	rare^b	none	Anti-PP1P^k
P₁^k	rare	P1, P^k	Anti-P
P₂^k	rare	P^k	Anti-PP1

^a These frequencies differ significantly between different populations. E.g. the frequency of P₁ vs. P₂ are virtually the opposite when Caucasians (80 vs. 20%) and Japanese (20 vs 80%) are compared.
^b While the frequency of this phenotype has been estimated at 1 per million, two population groups, Swedes and Amish people, have significantly higher numbers (e.g. 141 per million in Västerbotten county in Northern Sweden [21]).

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