Gnathodiaphyseal Dysplasia (GDD) characterized by enhanced bone mass and spontaneous fractures is a rare autosomal dominant genetic disease caused by Anoctamin 5 (ANO5) mutations. Deletion or mutation in ANO5 exhibited abnormal bone metabolism of GDD manifested by increased osteogenesis and reduced osteoclastogenesis. However, the mechanism is not fully understood. Ano5Cys360Ty r knock-in mouse model was used. Mouse calvarial osteoblast (mCOB) and bone marrow macrophage (BMM) from homozygous knock-in (Ano5KI/KI) and wildtype mice were cultured in vitro. Compound C was selected to inhibit AMPK activity. We found that Ano5Cys360Ty r mutation accelerated glycolysis and PGC1a-dependent mitochondrial respiration of osteoblast. Abnormal mitochondrial structure and function caused by PGC1b downregulation was observed in Ano5 KI/KI osteoclast. Furthermore, ANO5 mutation promoted the phosphorylation of AMPK, the classical sensor of energy metabolism. Inhibiting AMPK reduced glycolysis in osteoblast and maintained the mitochondrial homeostasis between osteoblast and osteoclast by suppressing PGC1a and promoting PGC1b respectively, to restrain bone formation and restore osteoclastogenesis. AMPK inhibitor reversed the bone phenotype of GDD by restraining bone formation and restoring osteoclastogenesis. We highlighted the critical role of glucose metabolic distemperedness mediated by AMPK activation in GDD, which developing a potential therapeutic strategy targeted for treatment of GDD.

Gnathodiaphyseal dysplasia (GDD) is a rare autosomal dominant genetic disease, mainly characterized by enlargement of the mandible, osteosclerosis, and frequent fracture of tubular bone. GDD is caused by heterozygous mutations in Anoctamin 5 (ANO5). We have previously generated an Ano5 knockout (KO) mice model and validated the phenotypes consistent with GDD patients, including enhanced bone formation and alkaline phosphatase (ALP) activity. Experiments have identified that Ano5 deficiency elevated the osteogenesis of calvaria-derived osteoblasts (mCOBs). In this study, we found that Ano5 deficiency notably inhibited miR-34c-5p expression. Krüppel-Like Factor 4 (Klf4), a target gene of miR-34c-5p confirmed by dual luciferase reporter assay, was up-regulated in Ano5-/- mCOBs, accompanied by activated downstream canonical Wnt/β-catenin signaling and increased expression of β-catenin. Overexpression of miR-34c-5p in Ano5-/- mCOBs inhibited osteogenic capacity by suppressing proliferative capacity, osteoblast-related factor levels, ALP activity, and matrix calcification through regulating KLF4/β-catenin signaling axis. Furthermore, miR-34c-5p adeno-associated virus (AAV) treatment in vivo rescued the abnormally thickened cortical bone and enhanced biomechanical properties in Ano5-/- mice. Importantly, the serum level of P1NP, a marker of bone formation, was also significantly declined. We conclude that dysregulation of miR-34c-5p contributes to the enhanced osteogenesis in GDD by excessive activation of KLF4/β-catenin signaling axis under Ano5-deficient conditions. This study elucidates the pathogenesis of GDD and provides novel insights into the therapeutic strategies.

Gnathodiaphyseal dysplasia (GDD) is a rare genetic syndrome characterized by cemento-ossifying fibroma lesions in the mandible and sclerosis of tubular bones. Currently, the clinical treatment of GDD is limited to surgical resection; therefore, novel treatment strategies developed through exploration of the related mechanisms are needed. Mutations in the TMEM16E/ANO5 gene are considered the main pathogenic factor of GDD, and the Ano5 knockout mouse model (Ano5-/-) established previously, which presented GDD-like characteristics, exhibited decreased osteoclastogenesis. ANO5, a calcium-activated chloride channel (CaCC), plays an important role in the maintenance of intracellular calcium homeostasis, which is crucial for osteoclast differentiation. In this study, our data indicated that the intracellular calcium concentration ([Ca2+]i) and calcium transients were significantly decreased in Ano5-/- osteoclasts accompanied by abnormally altered expression of calcium transporters, resulting in calcium dyshomeostasis. In addition, the endoplasmic reticulum stress (ERS) response was significantly enhanced in Ano5-/- osteoclasts, possibly because of calcium dyshomeostasis, which leading to the increased proportion of apoptotic osteoclasts via the activation of the C/EBP homologous protein (CHOP) signalling pathway, accompanied by abnormal changes in the expression of apoptosis-related factors. In summary, Ano5 deficiency impairs the function of osteoclasts by increasing osteoclast apoptosis, which is induced by an overactivated ERS response via calcium dyshomeostasis.

Gnathodiaphyseal Dysplasia is a rare autosomal-dominant disease caused by a mutation in GDD1. Patients typically present with pathological fractures, muscle weakness, and jawbone deformities. This genetic disorder has long been misdiagnosed until 2004 when the genetic basis of this disorder was identified, differentiating it from Osteogenesis Imperfecta and Fibrous Dysplasia. However, clinicians are still largely unaware of this entity and continue to label and treat it as a variation of Osteogenesis Imperfecta. This report describes a 21-year-old male with GDD presenting with numerous fractures and Angle Class III malocclusion. He was treated with LeFort 1 advancement and Bilateral Sagittal Split Osteotomy of the mandible with setback procedures. No complications were seen and 2-year follow-up showed stable dental occlusion. This is the first report describing orthognathic surgery safely performed on a patient with GDD1. Other procedures are possible, but more research is needed to develop best practices for this disorder. CONSENT AUTHORIZATION: The patient provided written consent for publication of the clinical photos.

Gnathodiaphyseal dysplasia (GDD) is an autosomal dominant syndrome characterized by bone fragility, sclerosis of tubular bones, and cemento-osseous lesions of the jawbones. This report describes the long-term radiographic follow-up study of jaw lesions in a GDD-affected woman of >40 years of age from the age of one onward. At three years of age, widening of the diaphyseal cortices in the femur and radius was observed, although no symptoms were observed in the jawbones. At nine years of age, we observed a slightly sclerotic appearance in the alveolar and jawbones adjacent to the permanent tooth roots. After completion of the secondary dentition at 14 years of age, increased density of the sclerotic mass was clearly observed. Although the etiology and pathogenesis are uncertain, this study observed that the onset of the jawbone lesion had already appeared after the mixed dentition stage, and the sclerotic mass developed with age.