PI Mtoyoura: A new PI M subtype found by separator and hybrid isoelectric focusing

In the course of a population study of α 1 ‐antitrypsin polymorphism by separator isoelectric focusing, a variant phenotype having a somewhat narrower spacing than PI M1M3 was observed in a Japanese blood donor. Family studies by hybrid isoelectric focusing in a carrier ampholyte‐supplemented immobilized pH gradient from 4.35–4.65 revealed that the products of the responsible gene, PI * Mtoyoura , were extremely close but slightly cathodal to those of PI * M1. The difference in isoelectric point between them corresponded to the resolving limit of isoelectric focusing. For this reason, although the propositus' father was deduced to have the genotype PI * M1 / PI * Mtoyoura , the products of these two genes failed to form a double band pattern. Thus, the gene frequency for PI * Mtoyoura was unknown. These findings, however, indicate that a further microheterogeneity in the PI M subtype exists at least in the Japanese.