BACKGROUND: Bone tissue homeostasis relies on the coordinated activity of the bone-forming osteoblasts and bone-resorbing osteoclasts. Osteomesopyknosis is considered a distinctive rare sclerosing skeletal disorder of unelucidated pathophysiology and presumably autosomal dominant transmission. However, the causal genes are unknown.
METHODS: We present a case report encompassing clinical assessments, imaging studies, and whole-exome sequencing analysis, complemented by functional in vitro experiments.
RESULTS: This new case of osteomesopyknosis was associated with a missense ALOX5 variant predicted to induce protein misfolding and proteasomal degradation. Transfection experiments demonstrated that the variant was associated with reduced protein levels restored by proteasomal inhibition with bortezomib. Likewise, gene expression analysis showed that the mutated gene was associated with a decreased RANKL/OPG ratio, which is a critical driver of osteoclast precursor differentiation.
CONCLUSIONS: Our data indicate impaired bone resorption as the underlying mechanism of this rare osteosclerosis, implicating ALOX5 pathogenic variants as potential etiological factors.

BACKGROUND: The clavicle is a long bone that forms the anterior border of the thoracic inlet. Anatomic abnormalities of the clavicle can lead to compression of the innominate artery and trachea due to mass effect. These anatomic abnormalities can be amenable to surgical resection, which can provide complete resolution of symptoms.
METHODS: We present a case of tracheal compression by the innominate artery in an adult man, caused by a clavicular abnormality due to an underlying bone mineralization disorder, corrected by partial resection of the right clavicle.
RESULTS: The patient underwent successful open surgical resection of his right clavicular head leading to resolution of his tracheal compression by the innominate artery.
CONCLUSIONS: We believe that this is the first description of tracheal compression due to osteomesopyknosis. This case demonstrates that compression of the innominate artery due to a clavicular abnormality can be safely corrected via open surgical resection.

We report two cases of an axial osteosclerosis with histopathologic findings of osteomesopyknosis in siblings. Osteomesopyknosis is a benign hereditary osteosclerosis that can show a radiologic pattern similar to blastic metastatic disease. The aim of this article is to inform radiologists about the existence of this benign condition and its various radiologic manifestations. Therefore, we discuss the principal differential diagnosis and point out the key imaging findings of osteomesopyknosis in order to avoid overdiagnosis in future cases.