An unusual type of alpha1-antitrypsin deficiency in a child.

An unusual variant of serum alpha1-antitrypsin is described in a 15 5/6-year-old white male with a history of chronic pulmonary disease. The patient had a very low level of this protease inhibitor as demonstrated by tryptic inhibitory capacity and electroimmunoassay. Even though the patient's serum alpha1-antitrypsin was partially purified and concentrated, no phenotypic pattern was seen using conventional Pityping procedures (acid starch gel with crossed antigen-antibody electrophoresis or isoelectric focusing). Crossed antigen-antibody electrophoresis using agarose in both steps, immunoelectrophoresis, and agarose electrophoresis followed by immunofixation all revealed a slow-moving alpha1-antitrypsin, cathodal to the Pi Z region. Studies on sera from the patient's mother and two half-sibs showed that all three had clear Pi M phenotypic pattersn. Quantitative date on these sera suggested that the unusual variant may be inherited in a codominant fashion.