A patient with pycnodysostosis presenting with seizures and porencephalic cysts

Unravelling the Relacatib activity against the CTSK proteins causing pycnodysostosis: a molecular docking and dynamics approach

Pycnodysostosis is an atypical autosomal recessive condition of Lysosomal storage disorder that originated due to the deficit of the enzyme Cathepsin K which is vital for normal osteoclast action in bone resorption. Abnormal degradation of type 1 collagen and accumulation of toxic undigested collagen fibers in lysosomes of the osteoclast cells resulting in high bone density, brittle bones, and a short stature is caused in CTSK protein-carrying individuals. The broad aim of this study is to identify the most significant variant through various computational pipelines. This study was initiated by retrieving a total number of thirty-six variants from NCBI, HGMD, and UniProt databases, and the Y283C variant was found to be more significant by various standard computational tools. A structural investigation was performed to understand and gain a better knowledge about the interaction profile for the native (1BY8) and variant (Y283C) with Relacatib (a small-molecule drug that blocks the function of Cathepsin K, an enzyme that has been linked to osteoporosis, osteoarthritis, and other bone-degrading diseases). The interaction profile was analyzed using molecular docking. Relacatib (ligand) had an average binding affinity for both native (-7.16 kcal/mol) and Y283C (-6.76 kcal/mol). Finally, Molecular dynamics simulations were done in duplicates to recognize the variant (Y283C) activity of the protein structure against Relacatib for 100 ns. This study assists in comprehending the most pathogenic amino-acid variant, the ligand interaction with the protein structure, and paves the way for understanding the steadiness of the ligand with the native and selected significant amino-acid variant.Communicated by Ramaswamy H. Sarma.

Orthopedic Treatment of Pycnodysostosis: A Systematic Review

Pycnodysostosis (PYCD) is an autosomal recessive lysosomal storage disorder of the bone which leads to stereotypical abnormalities consisting of, but not limited to, sclerotic and fragile bone, shortened distal phalanges, and obtuse mandibular angle. Current literature describes the otolaryngological manifestations and treatment of this disorder; however, the treatment of orthopedic fractures in PYCD patients is seldom described and remains a controversial topic. We aim to systematically review the current evidence regarding the optimal treatment of PYCD patients with fractures.

We performed a literature search using PubMed, MEDLINE, Web of Science, and Google Scholar databases. Elig­ibility criteria consisted of English-language literature of PYCD patients undergoing treatment for orthopedic surgery fractures. Non-English papers or literature focused on maxillofacial manifestations/treatment were excluded.

The database search resulted in the identification of 500 articles. After removing duplicates and enforcing our inclusion criteria, 29 case reports/series (40 patients) were included. The average age was 31.25 (­±18.2) years, with 57.5% of patients being female. Overall, 62.5% of patients had consanguineous parents. Additionally, 86.2% reported a history of previous fractures while 47.5% reported a spontaneous or minor trauma fracture, with most fractures occurring in the femur (60.0%) and tibia (40.0%). Radiographic features consisted of densification in the femur 45.0% (18/40), tibia 37.5% (15/40), and spine 25.0% (10/40). Overall, 84.2% of patients were treated with surgical management consisting of internal plate fixation (IPF) (48.3%), intramedullary fixation (20.7%), and Ilizarov external fixation (IEF) (13.8%). Overall, the refracture rate was 25.0% and was lowest in intramedullary fixation (0/6), compared to IPF (3/14) and IEF (3/4). Average time until refracture was 40.6 months (3-132 months).

Long-term follow-up is recommended in patients with PYCD due to the propensity for fractures/refractures. While this study provides the groundwork for the treatment of PYCD patients, further research with higher-evidence studies should be conducted to establish the optimal orthopedic treatment of this disorder.

Pycnodysostosis- a rare disorder with distinctive craniofacial dysmorphia. A case report

Pycnodysostosis is a rare autosomal recessive condition caused by the mutation of CTSK gene. CTSK regulates the activity of Cathepsin K which is responsible for osteoclast-mediated bone resorption. This mutation causes the bones to become dense, sclerotic, brittle, and thus, prone to fracture. Affected individuals have normal cognitive development and life expectancy, however, the quality of life depends on the early diagnosis of the condition. The patient presents with striking clinical (short stature, brachydactyly) and radiological (frontal and parieto-occipital bossing, open sutures, and fontanelles, acro-osteolysis of terminal phalanges) features making the diagnosis clinico-radiographic. In atypical or mild cases with overlapping features, gene mapping is advocated. A plethora of dental anomalies and characteristic craniofacial dysmorphia puts the dentist in a position to diagnose such a case.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

The role of cathepsin K in oral and maxillofacial disorders

Cathepsin K (CTSK) was thought to be a collagenase, specifically expressed by osteoclasts, and played an important role in bone resorption. However, more and more research found that CTSK was expressed in more extensive cells, tissues, and organs. It may not only participate in regulating human physiological activity, but also be closely related to a variety of disease. In this review, we highlight the relationship between CTSK and oral and maxillofacial disorders on the following three aspects: oral and maxillofacial abnormities in patients with pycnodysostosis caused by CTSK mutations, oral and maxillofacial abnormities in Ctsk(-/-) mice, and the role of CTSK in oral and maxillofacial diseases, including periodontitis, peri-implantitis, tooth movement, oral and maxillofacial tumor, root resorption, and periapical disease.