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Ectopic mineralization - inappropriate biomineralization in soft tissues - is a frequent finding in physiological aging processes and several common disorders, which can be associated with significant morbidity and mortality. Further, pathologic mineralization is seen in several rare genetic disorders, which often present life-threatening phenotypes. These disorders are classified based on the mechanisms through which the mineralization occurs: metastatic or dystrophic calcification or ectopic ossification. Underlying mechanisms have been extensively studied, which resulted in several hypotheses regarding the etiology of mineralization in the extracellular matrix of soft tissue. These hypotheses include intracellular and extracellular mechanisms, such as the formation of matrix vesicles, aberrant osteogenic and chondrogenic signaling, apoptosis and oxidative stress. Though coherence between the different findings is not always clear, current insights have led to improvement of the diagnosis and management of ectopic mineralization patients, thus translating pathogenetic knowledge (variome) to the phenotype (phenome). In this review, we will focus on the clinical presentation, pathogenesis and management of primary genetic soft tissue mineralization disorders. As examples of dystrophic calcification disorders Pseudoxanthoma elasticum, Generalized arterial calcification of infancy, Keutel syndrome, Idiopathic basal ganglia calcification and Arterial calcification due to CD73 (NT5E) deficiency will be discussed. Hyperphosphatemic familial tumoral calcinosis will be reviewed as an example of mineralization disorders caused by metastatic calcification.

Mineralization of soft tissues is an abnormal process that occurs in any body tissue and can greatly increase morbidity and mortality. Vitamin K-dependent (VKD) proteins play a crucial role in these processes; matrix Gla protein is considered one of the most relevant physiological inhibitors of soft tissue calcification know to date. Several studies have suggested that other, still unknown, VKD proteins might also be involved in soft tissue calcification pathologies. We have recently identified in sturgeon a new VKD protein, Gla-rich protein (GRP), which contains the highest ratio between number of Gla residues and size of the mature protein so far identified. Although mainly expressed in cartilaginous tissues of sturgeon, in rat GRP is present in both cartilage and bone. We now show that GRP is a circulating protein that is also expressed and accumulated in soft tissues of rats and humans, including the skin and vascular system in which, when affected by pathological calcifications, GRP accumulates at high levels at sites of mineral deposition, indicating an association with calcification processes. The high number of Gla residues and consequent mineral binding affinity properties strongly suggest that GRP may directly influence mineral formation, thereby playing a role in processes involving connective tissue mineralization. (Am J Pathol 2009, 175:2288-2298; DOI; 10.2353/ajpath.2009.090474) NHLBI NIH HHS [HL58090, R01 HL058090] info:eu-repo/semantics/publishedVersion