Diagnosis and treatment of Paget's disease of bone: a mini-review

Multimodal regulation of the osteoclastogenesis process by secreted group IIA phospholipase A2

Increasing evidence points to the involvement of group IIA secreted phospholipase A₂ (sPLA₂-IIA) in pathologies characterized by abnormal osteoclast bone-resorption activity. Here, the role of this moonlighting protein has been deepened in the osteoclastogenesis process driven by the RANKL cytokine in RAW264.7 macrophages and bone-marrow derived precursor cells from BALB/cJ mice. Inhibitors with distinct selectivity toward sPLA₂-IIA activities and recombinant sPLA₂-IIA (wild-type or catalytically inactive forms, full-length or partial protein sequences) were instrumental to dissect out sPLA₂-IIA function, in conjunction with reduction of sPLA₂-IIA expression using small-interfering-RNAs and precursor cells from Pla2g2a knock-out mice. The reported data indicate sPLA₂-IIA participation in murine osteoclast maturation, control of syncytium formation and resorbing activity, by mechanisms that may be both catalytically dependent and independent. Of note, these studies provide a more complete understanding of the still enigmatic osteoclast multinucleation process, a crucial step for bone-resorbing activity, uncovering the role of sPLA₂-IIA interaction with a still unidentified receptor to regulate osteoclast fusion through p38 SAPK activation. This could pave the way for the design of specific inhibitors of sPLA₂-IIA binding to interacting partners implicated in osteoclast syncytium formation.

Clinical phenotype of adult offspring carriers of the p.Pro392Leu mutation within the SQSTM1 gene in Paget's disease of bone

Paget's disease of bone (PDB) is a common chronic bone disorder. In the French-Canadian population, the p.Pro392Leu mutation within the SQSTM1 gene is involved in 46% of familial forms. In New Zealand, the emergence of PDB in offspring inheriting SQSTM1 mutations was reported to be delayed by a decade compared to their parents. We aimed at assessing the clinical phenotype of offspring carriers of this mutation in our French-Canadian cohort. We reviewed research records from adult offspring carriers of this mutation aged <90 years and their affected parents. In parents, we collected data on sex, age at diagnosis, number of affected bones, total serum alkaline phosphatase levels (tALPs) at diagnosis. In offspring, PDB extended phenotype assessment relying on tALPs, bone specific alkaline phosphatase levels (bALPs), procollagen type 1 amino-terminal propeptide (P1NP), whole body bone scan and skull and pelvis radiographs, was performed at inclusion from 1996 to 2009 and updated in 2016 to 2018, if not done during the past 8 years. The results showed that among the 36 offspring with an updated phenotype, four of them developed a clinical phenotype of PDB characterized by monostotic or polyostotic increased bone uptake associated with typical radiographic lesions in the affected sites, representing an incidence of 1.83 per 1000 person-years. Moreover, the age at PDB diagnosis was delayed by at least 10 years in the adult offspring carriers of the p.Pro392Leu mutation versus their affected parents. Our findings support the utility of a regular monitoring of the adult offspring without PDB but carriers of this mutation.

Diffuse, fracturing systemic skeletal histiocytosis of unknown type: a novel metabolic bone disease

We describe a novel disease of diffuse skeletal histiocytosis associated with multiple fragility fractures and high osteoclast activity. Clinical, radiographic, biochemical, genetic, and histopathological investigations were performed to characterize the diagnosis of an Asian man who presented with hip fracture and diffuse skeletal lytic lesions. After excluding malignancy and other common metabolic bone diseases, open bone biopsy yielded several pathological samples all showing extensive skeletal histiocytosis likely to explain the diffuse axial and appendicular lytic lesions. Rare disorders such as Langerhans histiocytosis, Erdheim-Chester disease, and diffuse cystic skeletal angiomatosis were excluded through careful pathological examination and lack of CD1a and S-100 staining. Whole exome sequencing did not yield diagnostic findings to explain this likely acquired disease. High markers of osteoclast activity suggested excessive focal bone resorption but normalized after zoledronic acid treatment. A novel disease of skeletal histiocytosis with high bone turnover is differentiated from other histiocytic and lytic skeletal diseases.

DIAGNOSIS AND MANAGEMENT OF PAGET'S DISEASE OF BONE - SERIES OF 8 CASES

Paget's disease of bone is a chronic condition characterized by focal abnormalities of absorption and formation of bone, and it may lead to anatomical deformities, pain, fractures, and malignant transformation. It is common in the UK, Australia, New Zealand, and North America and has a strong hereditary component, affecting first- to third-degree relatives. The etiology remains unclear and treatment is based on control of the disease with bisphosphonates, with the aim of relieving symptoms and correcting laboratory abnormalities. Surgical treatment may also be necessary to correct deformities or treat pathological fractures. This study evaluated the management and course of 8 patients with Paget's disease of bone, followed in the Orthopedic Clinic of this hospital. Among these patients, 1 had concomitant advanced prostate carcinoma, highlighting the association between Paget's disease and secondary bone diseases that can affect the differential diagnosis. Level of evidence IV, Study type: Case Series.

Use of Zoledronic Acid in Paediatric Craniofacial Fibrous Dysplasia

We describe a case of a paediatric patient affected by mandibular fibrous dysplasia (FD) with severe and chronic pain who was successfully treated with zoledronic acid (ZOL): a third-generation bisphosphonate. Further research is needed to assess its safety and efficacy as a treatment option for FD in the paediatric population.