SERPINA1 and lung disorder: On the other hand, AAT serum levels in PI*SS subjects are usually above the considered protective threshold of 0.5 g/L, and the S protein polymerizes very slowly, resulting in negligible hepatic accumulation and circulating polymer concentrations, leading PI*S to be considered as a non-polymerizing variant [4, 9, 21], thereby suggesting a very low (or non-existent) risk of lung disease in the majority of PI*SS individuals.