[Determination of alpha 1 antitrypsin phenotypes in plasma using isoelectric focusing on this agarose gel]

Plasma alpha 1 antitrypsin (alpha 1 AT) is the major serine protease inhibitor (Pi) in plasma. It is a glycoprotein, which presents many molecular variants. Allelic phenotypes are classified alphabetically according to their electrophoretic mobility in the Pi (Proteases inhibitor) system. More than 75 distinct protease inhibitor subtypes have been identified using isoelectric focusing (IEF). The major interest for detecting its microheterogeneity is the rare possibility of deficient alleles, which are responsible of low amounts in the alpha IAT production. The clinical use of the alpha 1AT phenotyping is the diagnosis of hereditary alpha 1AT deficiencies. The most common normal phenotype is MM; the major deficient phenotypes are MS, MZ, SS, SZ and ZZ. Hereditary deficiencies of the Pi, the most common inborn error in European people, lead to pulmonary emphysema in young adults or liver cirrhosis in children. IEF on polyacrylamide gels is the reference method for alpha 1AT phenotyping, but is very difficult to standardize. In the present study, we have developed IEF on agarose gels for Pi subtyping within a number of technical improvements. A 0.5 mm thin agarose gel (1.6%) is cast on polyester film; focusing is performed using carrier ampholines (pH = 4.2-4.9), using a very high voltage. Staining is done with a simplified silver nitrate method. The patterns of the different Pi phenotypes obtained with our technique are very attractive. The common subtypes corresponding to the alleles M1, M2, M3, S, Z are univocally demonstrated. Agarose gel allows the advantage of using a non toxic substance. Further the gels are easy to produce and the method is accessible to all clinical laboratories.