pediatrics
Osteosclerosis
Pyknodysostosis
This Autosomal Recessive is caused by loss of function mutations in the gene encoding cathepsin K, an osteoclast-derived protease important in degradation of extracellular bone matrix. Short stature becomes evident in early childhood; adult height is≤150 cm (5 ft). Other manifestations include an enlarged skull, short and broad hands and feet, short sclerotic terminal phalanges, dystrophic nails, and retention of primary teeth. Blue sclerae (due to a deficiency in connective tissue allowing the underlying vessels to show through) are usually recognized during infancy. Affected people resemble each other closely; they have a small face, a receding chin, and carious, misplaced teeth. The cranium bulges, and the anterior fontanelle remains patent. Pathologic fractures are a complication of pyknodysostosis. This photo shows a receding chin in a boy with pyknodysostosis. © Springer Science+Business Media This photo shows short, broad hands and dysplasia of terminal phalanges (particularly of the thumbs) in a man with pyknodysostosis. © Springer Science+Business Media This photo shows a close-up of the eye showing a blue sclera (normally white). JAMES STEVENSON/SCIENCE PHOTO LIBRARY Diagnosis of pyknodysostosis is suspected by the presence of blue sclerae, short stature, and characteristic skeletal features. Typically, plain x-rays are done. Bone sclerosis appears on x-rays during childhood, but neither bone striations nor endobones (bone within bone) are seen. Facial bones and paranasal sinuses are hypoplastic, and the mandibular angle is obtuse. Clavicles may be gracile, and their lateral portions may be underdeveloped; distal phalanges are rudimentary. Plastic surgery has been used to correct severe deformities of the face and jaw. 