Pi phenotypes of alpha1-antitrypsin in Southern England: identification of M subtypes and implications for genetic studies.

Phenotypes of alpha1-antitrypsin (A1AT) were determined by isoelectric focusing in blood samples from 926 healthy Caucasians living in South-West England. Three subtypes of the most common allele product (M), designated M1, M2, and M3, were identified. Routine determination of these subtypes should considerably amplify the usefulness of the A1AT polymorphism in population genetics and, in view of the possible association of clinical disorders with heterozygous deficient M phenotypes, may enhance the value of Pi determinations in clinical genetics.