Based on the evidence that periostin is specifically involved in intra-cortical remodeling control, our working hypothesis is that assessment of its concentration in the serum would be helpful in identifying patients with severe cortical porosity, a critical parameter in bone fragility. Periostin expression by osteoblasts and osteocytes is part of the bone cortical response to anabolic stimuli such as mechanical strain or intermittent increase in parathyroid hormone. However, it remains unknown whether this expression may participate as well to mechanisms that will lead to exaggerated intra-cortical remodeling and subsequent bone loss.

In rare clinical situations in which trans-iliac bone biopsies will be necessary to better understand their bone status in addition to densitometry and biological bone markers assessment, specific analyses using immune-staining techniques will be performed on the bone sample. Data from routine follow-up every six months will be also collected in this specific sub-group.

High resolution peripheral quantitative computerized tomography (HR-pQCT) gives the opportunity of performing a virtual bone biopsy providing information on trabecular and cortical microarchitecture in vivo. These microarchitectural parameters allow a more accurate evaluation of the alteration of the bone structure and therefore of the fracture risk as compared to current tools used in clinical practice such as densitometry. However, the availability of such HRpQCT facilities is limited and there is on-going development on the best way of measuring porosity for example. The definition of a biological profile including key proteins such as periostin and sclerostin involved in porosity mechanisms is therefore of great interest. A better understanding of the relationship between bone matrix components and parathyroid hormone effects also appears as critical. Follow-up of routine evaluation parameters reflecting bone status in a subgroup of specific patients could also provide new and additional information.

Inclusion Criteria:

• Hyperparathyroidism defined by a parathyroid hormone serum level above 65 ng/ml, secondary to Chronic Kidney Disease (CKD) ou vitamin D deficiency

Exclusion Criteria:

• Concurrent bone disease (such as Paget's disease, osteomalacia),
• Other endocrinopathy having an impact on bone metabolism (such as Cushing, hyperthyroidism, severe hypogonadism (except menopause)),
• Current or previous bisphosphonate treatment.
• Transplantation
• parathyroidectomy
• Life expectancy less than 3 months.
• Lack of study understanding.
• Lack of agreement.
• Under legal control.