ESPE Abstracts

Background: Hypophosphatemic rickets (HR) is a group of rare disorders caused by excessive renal phosphate wasting. The dominant form of HR is X-linked HR (XLHR) caused by mutation in the phosphate-regulating endopeptidase gene PHEX. There is also autosomal dominant form of HR caused by mutation in FGF23 gene or rare autosomal recessive form caused by DMP1 mutation. The phenotype can vary from very delicate to severe bone disease.

Objective and hypotheses: The aim of the study was to investigate the clinical and molecular background of HR in five patients.

Method: Five patients aged 2–8 years (two girls and three boys) were diagnosed with HR due to clinical and biochemical picture. In each of these patients three exons of the FGF23 gene were directly sequenced after PCR amplification of the entire coding region. Additionally, in one patient PHEX gene was also analyzed by direct sequencing (in the four remaining the analyses are ongoing).

Results: i) Bowing of legs was the dominant symptom in all patients. ii) All patients presented hypophosphatemia, increased loss of phosphorus with urine, increased alkaline phosphatase with normal serum calcium and 25OHD3. The TRP was low only in two children. iii) In one patient analysis of the FGF23 gene revealed the presence of one polymorphism c.C716>T, p.T239M. The remaining four patients were FGF23 mutation-negative. In one patient the already known PHEX gene deletion was found encompassing exons 17–22.

Conclusion: The early diagnosis of HR is very important for proper treatment and to prevent bone deformities. The molecular analysis of FGF23 and PHEX gene is very important for the confirmation of clinical diagnosis of HR and highlights the role of further genetic counselling in families with HR patients.