Pycnodysostosis

A rare genetic disorder affecting bone density

Classification
External resources

Pycnodysostosis is a rare genetic disorder characterized by osteosclerosis, or increased bone density, due to a defect in the cathepsin K gene. This condition leads to a variety of skeletal abnormalities and is inherited in an autosomal recessive pattern.

Signs and Symptoms

Individuals with pycnodysostosis typically present with short stature, delayed closure of the fontanelles, and osteosclerosis. Other common features include:

• Craniofacial abnormalities such as a prominent forehead, a small jaw (micrognathia), and a high-arched palate.
• Dental abnormalities, including delayed eruption of teeth and dental crowding.
• Brittle bones that are prone to fractures.
• Clubbing of fingers and nail dysplasia.
• Hypoplasia of the distal phalanges, leading to acro-osteolysis.

Genetics

Pycnodysostosis is caused by mutations in the CTSK gene, which encodes the enzyme cathepsin K. This enzyme is crucial for the normal breakdown of collagen in the bone matrix. Mutations in this gene lead to impaired bone resorption, resulting in the characteristic increased bone density and fragility.

Diagnosis

Diagnosis of pycnodysostosis is based on clinical evaluation, family history, and radiographic findings. X-rays typically show increased bone density, acro-osteolysis, and delayed closure of cranial sutures. Genetic testing can confirm mutations in the CTSK gene.

Management

There is no cure for pycnodysostosis, and treatment focuses on managing symptoms and preventing complications. This may include:

• Orthopedic surgery to manage fractures and skeletal deformities.
• Dental care to address dental abnormalities.
• Growth hormone therapy in some cases to improve growth.
• Regular monitoring by a multidisciplinary team including endocrinologists, orthopedic surgeons, and dentists.

Prognosis

The prognosis for individuals with pycnodysostosis varies. While the condition is associated with increased risk of fractures and dental issues, many individuals lead relatively normal lives with appropriate management.

Related pages

• Osteopetrosis
• Cathepsin K
• Genetic disorders
• Autosomal recessive inheritance