| Summary: | Introduction. X-linked hypophosphatemic rickets (XLHR) is a dominant
inherited disease caused by isolated renal phosphate wasting and impairment
of vitamin D activation. We present a girl with X-linked hypophosphatemic
rickets (XLHR) as a consequence of de novo mutation in the PHEX gene. Case
Outline. A 2.2-year-old girl presented with prominent lower limb rachitic
deformity, waddling gait and disproportionate short stature (79 cm, <P5;
-1,85 SD). On the basis of hypophosphatemia, hyperphosphaturia, high serum
level of alkaline phosphatase, normal calcemia, 25(OH)D and PTH, as well as
characteristic clinical and X-ray findings, diagnosis of hypophosphatemic
rickets (HR) was made. Normal calciuria and absence of other renal tubular
disorders indicated HR as a consequence of isolated hyperphosphaturia. The
treatment (phosphate 55 mg/kg and calcitriol 35 ng/kg per day), introduced 15
month ago, resulted in a stable normalization of alkaline phosphatase and
phosphorus serum levels (with intact calcemia and calciuria), disappearance
of X-ray signs of the active rickets and improvement of the child’s
longitudinal growth (0.6 cm per month). Subsequently, by detection of already
known mutation in the PHEX gene: c.1735G>A (p.G579R) (exon 17), XLHR was
diagnosed. Analysis of the parental PHEX gene did not show the abnormality,
which indicated that the child’s XLHR was caused by de novo mutation of this
gene. Conclusion. Identification of genetic defects is exceptionally
significant for diagnosis and differential diagnosis of hereditary HR.
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