Bone Abstracts

Introduction: Hypophosphataemic rickets belongs to genetically determined rare disorders characterised by bone deformations, including varus deformity of the lower limbs and short stature. This type of rickets is related to renal phosphate wasting and hypophosphataemia. Less is known about bone turnover abnormalities and bone mass in this disease entity.

Aim: The aim of this study was to analyse bone turnover markers and bone mineral density in patients suffering from hypophosphataemic rickets being treated in our department.

Patients and methods: This study involved five children with hypophosphataemic rickets (two girls and three boys) aged 1–15. Levels of urine and serum calcium and phosphate, tubular reabsorption of phosphate, levels of hepatic and renal vitamin D3 and parathormone metabolites were assessed in patients. Bone turnover markers, such as alkaline phosphatase, as well as osteocalcin and pirydynolin were analysed. Bone mineral density was determined by densitometry with dual X-ray absorptiometry (DXA) using total body and spine programmes. A quantitative ultrasound assay (QUS) of the tibia and radius was also performed.

Results: Hyperphosphaturia was observed in all cases (6/6), while hypophosphataemia was present in 4/5 patients. Concentrations of vitamin D and PTH metabolites were normal, except for one girl, who did not follow therapeutic recommendations. We observed an increase in the bone formation markers in 4/5 patients, while an increase in bone resorption rates in 3/5 cases. Bone mineral density was reduced in one patient, whereas increased Z-score were observed in two children. A significant decrease in indicators of quantitative ultrasound examination for the tibia and/or radial bone were observed in all analysed patients.

Conclusions:
• Typical biochemical symptoms in hypophosphataemic rickets may be accompanied by accelerated bone turnover. Therefore, it is advisable to monitor bone formation and resorption markers in this disease.
• Disorders of mineral metabolism in hypophosphataemic rickets may reveal both an increase and reduction in bone mineral density.
• The reduction in parameters of the quantitative ultrasound in all investigated patients indicates worse bone quality in this disease.

Acknowledgements: The paper has been financed using funds of the statutory work No. 503/1-090-02/503-11-02 and as part of the NN407 060 938 grant.

Disclosure: The authors declared no competing interests.