Pycnodysostosis is an autosomal recessive skeletal disorder caused by deficiency of cathepsin K in the metabolism of the skeletal system, causing defects in bone resorption and bone remodeling. Pycnodysostosis is characterized by short stature, osteosclerosis, acroosteolysis, separated cranial sutures with open fontanelles, bone fragility, and loss of mandibular angle.