Clinical and molecular characterisation of new variants associated to alpha-1- antitrypsin deficiency

Abstract

Background: Alpha-1-antitrypsin deficiency (AATD) is a genetic disorder associated with pulmonary and liver disease. The pathogenic AAT variants generally have folding defects leading to toxic aggregation within hepatocytes, and a correlated plasma deficiency that results in uncontrolled protease activity in the lungs.

Aims and objectives: Using a multidisciplinary approach, we analysed a panel of 17 new AAT missense variants found in patients with suspected AATD from the Italian and Irish AATD reference centers.

Methods: The AAT variants were first identified based on a diagnostic algorithm that comprises the quantification of AAT and C reactive protein, the AAT phenotyping and the genotyping by SERPINA1 whole gene sequencing. A bioinformatic analysis of the variants was performed with the pathogenicity predictor REVEL and the likely pathogenic ones were selected for characterisation in mammalian cell models.

Results: Six putatively pathogenic AAT variants were expressed in either HEK293T or Hepa1.6 cells to investigate secretion efficiency and tendency to form intracellular polymers. Two AAT variants with high REVEL scores displayed a Z-like impact, with accumulation of mAb 2C1-positive polymers and severely impaired AAT secretion, while three other variants showed a milder deficiency profile.

Conclusions: Our work provides an example of how clinical data, bioinformatic predictions and biochemical analysis can be integrated to better define the pathogenic impact of novel rare AAT variants. Moreover, we characterised two new variants with Z-like behaviour, namely D341Y (Smilano) and L383P (Mcampolongo).