Concerning A1ATd, one of the most frequent causes of NC, diagnosis is efficiently performed through the assessment of α1AT serum levels, which if decreased, indicates the use of protease inhibitor (PI) typing through polyacrylamide isoelectric focusing or genotyping (PI-M, PI-S, PI-Z alleles) [27,72,78]. This evidence concerns the gene SERPINA1 and nevus comedonicus syndrome.