Sera from different populations (Dutch, Northern and Southern Italians and Spaniards) were screened for PI (alpha 1-antitrypsin) types and subtypes. A polyacrylamide isoelectric focusing method was applied, which consisted of the combined use of an ultra-thin highly cross-linked gel, restricted pH range carrier ampholytes and a separator. This technique enabled easy typing and subtyping of all known PI phenotypes including PI*M subtypes. The frequency of the new PI*M4 allele was lowest of all PI*M alleles (0.0476 in The Netherlands, 0.0371 in Northern Italy, 0.0308 in Southern Italy and 0.0146 in Spain).
