Pycnodysostosis is a rare condition characterized by moderate short stature (1.35m to 1.5m), increased density of the bones (osteosclerosis/osteopetrosis), underdevelopment of the tips of the fingers with absent or small nails, an abnomal collarbone (clavicle), distinctive facial features including a large head with a small face and chin, underdeveloped facial bones, a high forehead and dental abnormalities. Pycnodysostosis is an autosomal recessive genetic condition. The gene has been mapped to the same location as the gene for cathepsin K on chromosome 1q21. The diagnosis of pycnodysostosis is based on physical features and X-ray findings. Molecular genetic testing is available. Management is symptomatic. Individuals need orthopedic monitoring, treatment of fractures, appropriate dental care, and craniofacial surgery may be needed. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.