Bone Abstracts

Sclerosing bone dysplasias (too much bone diseases) are divided into two major groups, one group caused by impaired bone resorption and the other by increased bone formation. The former comprises a group of osteopetrosis (disorders due to abnormal osteoclastogenesis or osteoclast dysfunction) with relatively homogeneous skeletal phenotypes. By contrast, the latter encompasses a complex group of disorders with heterogeneous pathogeneses and diverse skeletal phenotypes.

From the pathogenic viewpoint, the latter group is classified into several groups: i) a group of abnormal Wnt signaling (AD osteopetrosis type 1/endooseal hyperostosis Worth type, van Buchem disease, and sclerosteosis, osteopathia striata with cranial sclerosis, a subset of craniodiaphyseal dysplasia), ii) a group of increased TGFβ/BMP signaling (osteopoikilosis/melorheostosis and Camurati–Engelmann disease), iii) a group of dysregulation of pyrophosphate metabolism (AD craniometaphyseal dysplasia), iv) a group of dysregulation of prostaglandin or thromboxane metabolism (pachydemopriostosis, cranioosteoarthropathy, and Ghosal hematodiaphyseal dysplasia), and v) a heterogeneous group of disorders whose phenotypes are composed of bone changes seen in the disorders cited above, singly or in combination, and a subset of which is termed mixed sclerosisng bone dysplasia.

The clinical and radiological manifestations of these disorders are reviewed, mainly focusing on disorders with abnormal Wnt signaling and increased TGFβ/BMP signaling. Affected individuals have three medical problems. The first is the result of craniofacial hyperostosis (cranial nerve palsy and increased intracranial pressure). The second is painful limbs probably due to cytokine-induction during hyperostotic process. The third includes variable extraskeletal complications (non-progressive myopathy, myelofibrosis, synovitis, and skin changes). Painful limbs may be prominent in a group of increased TGFβ/BMP signaling and sometimes very devastating. Losartan that can suppress TGFβ signaling may be beneficial; yet, its experiences remain anecdotal and sometimes disappointing. New medical intervention is expected.

Disclosure: The author declared no competing interests.