Endocrine Abstracts

JOINT2708

Background: X-linked recessive hypophosphatemic rickets (XLH), also known as the Dent Disease, is a rare bone diasease which estimated prevalence is about 1 in 20.000 live births. It causes skeletal deformities, pain, stiffness and fatigue and impairs quality of life. Burosumab, a fully human IgG1 monoclonal antibody directed againist the fibroblast growth factor 23 (FGF 23), is a promising new drug in the treatment of hypophosphatemic rickets.

Case Report: A 26-year-old female patient was referred to the orthopedic clinic when she was 1 year old and noticed curvature in her legs. The patient with genu varum and coxa varum was consulted to the endocrinology department upon detection of hypophosphatemia and high alkaline phosphatase levels (Calcium:9,4, phosphorus: 2,1, Alkaline Phosphatase: 2440). Hypophosphatemic rickets was considered in the patient. And the patient received treatment with oral phosphate supplements and active vitamin D during childhood. In genetic analysis, PHEX mutation c.1645+1 G>A heterozygote was detected. No similar disease or mutation was detcted in her 3 sisters. The patient developed urinary incontinence when she was 4 years old. Urinary ultrasonography revealed that the right kidney was 65*23 mm, the left kidney was 70*27 mm, and type 3 nephrocalcinosis was detected in both kidneys. The 24-hour urine calcium, citrate and oxalate values of the patient were normal. After the age of 18, follow up began in the adult endocrinology department and conventional therapy was continued. Subcutaneous Burosumab treatment every 2 weeks was started in the patient whose phosphorus and vitamin D levels continued to be low despite conventional therapy and who developed hyperparathyroidism. There were no side affects releated to Burosumab treatment. At the followup 3 monts after the treatmet the patient report improvements in pain, mobility, physical function, energy, fatigue and mental wellbeing also there is improvement in laboratory values (f.e phosphorus levels increased from 2.1 to 3)(shown in Table 1 and Table2).

Conclusion: In our case we reported that a positive laboratory and clinical response with Burosumab treatment in the diagnosis of X-linked hypophosphatemic rickets, and observed no side effects developed in the short term. The lack of a significant improvement in 25-OH vitamin D and ALP values may be due to the early period. However, since Burosumab treatment is a new and promising option, its effectiveness and safety are unknown. We emphasize that there is a need for studies with more case reports and a larger number of patients to monitor long term effects.