Gene expression studies showed a significant increase in the mRNA expression of INHBA (6 folds; P = 0.001), ACVR2B (10.8 folds; P = 0.0003) and FST (3.1 folds; P = 0.02), and a significant decrease in the gene expression of INHBB (2.3 folds; P = 0.02), ACVR2A (3 folds; P = 0.003), smad2 (2.5 folds; P = 0.007), smad3 (2 folds; P = 0.03), smad4 (4 folds; P = 0.0004), smad6 (3 folds; P = 0.003) and smad7 (3.2 folds; P = 0.005) in the S-AOM group when compared with the control tissues. The gene discussed is SMAD4; the disease is infectious otitis media.