Common proteases of the respiratory tract include type II transmembrane serine proteases, cysteine proteases, and matrix metalloproteinases, the latter of which contribute to the pathogenesis of various lung diseases (cysteine proteases [189,190,191,192,193,194,195,196,197]; matrix metalloproteinases [198,199,200,201,202]). The gene discussed is CTSB; the disease is lung disorder.