In mice, the impacts of a homozygous Csf1r knockout mutation (Csf1rko) include perinatal mortality, postnatal growth retardation, increased bone density (osteopetrosis), global defects in brain development and abnormalities of the sensory nervous system, infertility and delayed pancreatic beta cell development (reviewed in [3,7]). The gene discussed is CSF1R; the disease is osteopetrosis.