They have fundamentally been undertaken in the USA and Europe, and among these mention should be made of the results of Yang et al. [26], who conducted a case–control study in the USA, which observed a 70% increase in risk of LC associated with AAT deficiency genotypes, with predominance of adenocarcinoma and squamous cell carcinoma lineages. This evidence concerns the gene SERPINA1 and laryngotracheoesophageal cleft.