Relationship between a mild alpha 1 proteinase inhibitor deficiency and respiratory symptoms in a family.

A 34-year-old man with pulmonary emphysema was found to have a mild alpha 1 proteinase inhibitor (alpha 1 PI) deficiency. alpha 1 PI status was investigated in this patient and in 35 members of his family. The alpha 1 PI investigations included alpha 1 PI concentration and phenotype and serum inhibitory capacity for trypsin and pancreatic elastase. Fifteen members of the family had alpha 1 PI concentration and inhibitory capacities below the lower normal limit. Five of these members were characterized by the heterozygous MP phenotype and the 10 others by an apparently homozygous M phenotype, in which the M allele may be associated with another unidentified deficiency allele. Two members of the family had alpha 1 PI concentration and elastase inhibitory capacity below the lower normal limits and trypsin inhibitory capacity within the normal range. They were both characterized by the MP phenotype. Six of these 17 members (three of PI type M and three of PI type MP) showed chronic pulmonary symptoms, whereas among the 19 alpha 1 PI non deficient members, no member had a history of significant pulmonary symptoms.