Characterization of Novel Missense Variants of SERPINA1 Gene Causing Alpha-1 Antitrypsin Deficiency.
SERPINA1 gene is highly polymorphic, with more than one hundred variants described in databases. The SERPINA1 encodes alpha-1 antitrypsin (AAT) protein, and the severe deficiency of AAT is a major contributor to pulmonary emphysema and liver diseases. We report seven new variants in Spanish patients with AAT deficiency. All variants involved amino acid substitutions in different exons: PiSDonosti (S+Ser14Phe), PiTijarafe (Ile50Asn), PiSevilla (Ala58Asp), PiCadiz (Glu151Lys), PiTarragona (Phe227Cys), PiPuerto Real (Thr249Ala) and PiValencia (Lys328Glu). The effect of these variants was analyzed to investigate their contribution to the disease. Mutant proteins were overexpressed in HEK293T cells and AAT expression, polymerization, degradation and secretion as well as anti-elastase activity were analyzed by PAS staining, western blot, pulse-chase and elastase inhibition assays. When overexpressed, S+S14F, I50N, A58D, F227C and T249A mutants formed intracellular polymers and did not secrete AAT protein. Two variants (E151K and K328E) did not form polymers and secreted AAT protein. However, K328E showed intracellular retention and reduced anti-elastase activity. In conclusion, we demonstrate that deficient variants may be more frequent than previously thought, and their discovery can only be possible by the complete sequencing of the gene and subsequent functional characterization. Better knowledge of SERPINA1 variants would improve diagnosis and care of AAT deficiency carriers.