Exon 1 of ref(2)Pdpp'.Pa.cCMa has been replaced with exon 1 of ref(2)P+++.O1.cCMa. This has replaced the d, p and p' polymorphisms that were present in the PB1 domain of ref(2)Pdpp'.Pa.cCMa with the '+' sequences present in ref(2)P+++.O1.cCMa.