One proposed mechanism involves multigene mutations, including heterozygosity for the cystic fibrosis transmembrane conductance regulator (CFTR) gene mutation, as well as certain connective tissue disorders that contribute to MAC infection, such as Marfan syndrome (49–51), congenital contractual arachnodactyly (52), and complete TYK2 deficiency in hyper-IgE syndrome (53). The gene discussed is CFTR; the disease is hyper-IgE syndrome.