Bone phenotypes in rheumatology – there is more to bone than just bone

Table 1 Biomarkers of bone and cartilage turnover in osteoporosis, osteopetrosis and fibrodysplasia ossificans progressive

Biomarker	Disease levels compared to healthy	Findings	References
Bone turnover
CTX-I	Osteoporosis: not diagnostic Osteopetrosis: increased in in vivo models	Osteoporosis: Reduced by anti-resorptive agents (eg. bisphosphonates and anti-RANKL	[28, 29]
PINP	Osteoporosis: not diagnostic	Osteoporosis: Modulated in response to pharmacological interventions such as bisphosphonates, anti-SOST and anti-RANKL.	[28, 29]
Osteocalcin	Osteoporosis: not diagnostic Osteopetrosis: reduced in ADOII patients FOP: inconclusive	Osteoporosis: Modulated in response to pharmacological interventions such as bisphosphonates, anti-sclerostin and anti-RANKL. FOP: Age dependent association with mortality	[28,29,30]
(B)ALP	Osteoporosis: not diagnostic Osteopetrosis: no difference in ADOII patients	Osteoporosis: Modulated in response to pharmacological interventions such as bisphosphonates, anti-sclerostin and anti-RANKL.	[28, 29, 31]
TRACP5b	Osteoporosis: Elevated compared to healthy controls Osteopetrosis: Increased in ADOII Increased in in vivo models	Osteoporosis: associated with markers of bone remodeling and BMD. Osteopetrosis: associated with increased fractures in ADOII patients	[32,33,34,35]

ADOII Autosomal dominant osteopetrosis, SOST Sclerostin, BMD Bone mineral density

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