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Serum tartrate-resistant acid phosphatase 5b and osteocalcin in human type II autosomal dominant osteopetrosis

Calcif Tissue Int 72, Abstract P27

Alatalo SL¹, Ivaska KK¹, Waguespack SG², Econs MJ³, Väänänen HK¹, Halleen JM¹

¹Institute of Biomedicine, Department of Anatomy, University of Turku, Turku, Finland
²Department of Endocrine Neoplasia and Hormonal Disorders, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA
³Departments of Medicine and Medical and Molecular Genetics, Indiana University, Indianapolis, IN, USA

Abstract

Autosomal dominant osteopetrosis type II (ADO2) is an uncommon metabolic bone disorder characterized by decreased bone resorption and significantly increased bone mass. The mutated gene in ADO2 is chloride channel 7 (ClCN7), which is needed for acidification of resorption lacunae. Patients with ADO2 have increased numbers of large ineffective osteoclasts and elevated serum levels of tartrate-resistant acid phosphatase (TRACP) and the BB isoenzyme of creatine kinase (CK-BB). We investigated the serum levels of the osteoclast-derived 5b isoform of TRACP (TRACP 5b) and the bone formation marker osteocalcin in ADO2 patients with known ClCN7 mutations. Ten ADO2 families participated in the current study. Based on radiographs, family history, and genotyping for ClCN7 gene mutations, 232 subjects were divided into three groups: clinically affected, carriers (with the ClCN7 mutation but no clinical evidence of disease), and healthy controls. The participants were further divided into children (aged from 2 to 18 years) and adult (aged >18 years) groups. The results are shown in table 1. Serum TRACP 5b levels were significantly elevated in affected patients compared with age-matched controls in both age groups, the values being several orders of magnitude higher than in any bone diseases with increased bone resorption. These results suggest that in ADO2, serum TRACP 5b reflects the number of osteoclasts rather than their activity, and that the extremely high serum TRACP 5b level is a specific indicator of the disease. Serum total osteocalcin levels were unchanged in children, but significantly decreased in adult carriers and significantly elevated in adult affected patients, suggesting that the balance in bone turnover may be disturbed in ADO2.