A final relevant point is related to the use of phenotyping instead of genotyping to characterize AAT genetic polymorphisms. Discrepancies are well known because of the limits of isoelectric focusing (IEF) and immunofixation.5 In particular, phenotyping is not able to detect Mlike and null variants. From our data, we calculated that the allele frequencies of rare detectable (I, E, F, N, P, V, X) and undetectable (Mlike, null) variants by IEF are 0.21% and 0.12%, respectively. The allelic frequencies of variants other than M, S, and Z in Donato et al’s2 and Bornhorst et al’s1 data were higher (> 1.0%). We can, therefore, speculate that the inclusion of undetectable variants such as Mlike and null resulted in a slight decrease in the lower limits of the reported reference values.