To further support the finding that osteoclastogenesis is promoted by malnutrition, we evaluated the expression of genes involved in osteoclastogenesis, Fos Proto-oncogene (Fos), cathepsin (Ctsk) and Receptor Activator of NF-κB Ligand (Rankl) in malnourished mice with and without inflammatory challenge. The gene discussed is FOS; the disease is nutritional deficiency disease.