Pycnodysostosis impacts bone growth and is present from birth. Symptoms include a large head and high forehead, undeveloped facial bones, and short fingers and toes. People with Pycnodysostosis may have short stature, dental abnormalities, brittle bones, and delayed closure of the skull bones. Bones may become more brittle with age. Other complications like trouble breathing during sleep (sleep apnea) and bone infections may occur. Pycnodysostosis is caused by a CTSK gene that is not working correctly and inherited in an autosomal recessive pattern. The diagnosis of Pycnodysostosis is based on clinical examination and X-ray findings, and is confirmed by genetic testing.