Pi M4: An additional Pi M subtype

Abstract
The authors studied Pi polymorphism using the Separator isofocusing method with slight modification. A new Pi allele was observed. Family pedigrees confirmed co-dominant inheritance with other Pi alleles. According to the electrophoretic mobility of its isoprotein bands, and to its frequency (0.04) this new allele is considered as a fourth Pi M subtype: Pi M4.