A new unstable PI M variant of alpha 1-antitrypsin in a Finnish isolate.

During family and population studies in a Finnish isolate (Salla), a variant of alpha 1-antitrypsin, tentatively called PI MSAL was found. On isoelectric focusing this variant was slightly cathodal to M3. With the aid of acid starch gel electrophoresis, differentiation from M3 proved reliable, because the variant was unstable in that system. The variant also showed an increased lability at + 56 degrees C and physiological pH and a decreased stability at pH 4.5 and room temperature compared to the other M subtypes. By genealogical studies it was possible to trace a common ancestor, a settler arriving to the parish around 1680, for the three families where the variant was found.