Mild A1AT deficiency can be caused by the S allele.  This codes for the Glu264Val substitution.   Notably, 1/4 of those living in the Iberian peninsula present this allele.  

Michigan State University

Homozygous or heterozygous S or Z allelic variants of A1AT lead to lower plasma levels of <0.9mg/mL. This can result in A1AT deficiency which is typically treated with intravenous augmentation therapy.  Serres and Blanco conducted a study to approximate the number of A1AT deficient genomes around the world and predicted that there are approximately 190 million with the following distribution:

- 75% are MS (slightly deficiency)
- 24% are MZ and SS (at risk for deficiency)
- 0.7% are SZ (increased risk for deficiency)
- 0.1% are ZZ (highest risk for deficiency)

A1AT Deficiency

de Loyola, M. B., dos Reis, T. T. A., de Oliveira, G. X. L. M., da Fonseca Palmeira, J., Argañaraz, G. A., & Argañaraz, E. R. Alpha‐1‐antitrypsin: A possible host protective factor against Covid‐19. Reviews in Medical Virology, e2157.
https://onlinelibrary.wiley.com/doi/full/10.1002/rmv.2157
doi: 10.1002/rmv.2157

Alpha‐1‐antitrypsin: A possible host protective factor against Covid‐19

Mild A1AT Deficiency

Severe A1AT deficiency can be caused by the Z allele.  Notably, 1/25 of those of European descent present this allele, and 1/2000 of this population are homozygous Z.  

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