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)