Background:

X-linked hypophosphatemia is the most prevalent form of heritable rickets,
characterized by an X-linked dominant inheritance pattern. The genetic basis of X-linked hypophosphatemia
is a loss-of-function mutation in the PHEX gene (Phosphate regulating gene with
Homology to Endopeptidases on the X chromosome), which leads to an enhanced production of
phosphaturic hormone FGF23. X-linked hypophosphatemia causes rickets in children and osteomalacia
in adults. Clinical manifestations are numerous and variable, including slowdown in
growth, swing-through gait and progressive tibial bowing, related to skeletal and extraskeletal actions
of FGF23. PHEX gene spans over 220 kb and consists of 22 exons. To date, hereditary and
sporadic mutations are known (missense, nonsense, deletions and splice site mutations).

Case Presentation:

Herein, we describe a male patient carrying a novel de novo mosaic nonsense
mutation c.2176G>T (p.Glu726Ter) located in exon 22 of PHEX gene.

Conclusion:

We highlight this new mutation among possible causative of X-linked hypophosphatemia
and suggest that mosaicism of PHEX mutations is not so uncommon and should be excluded
in diagnostic workflow of heritable rickets both in male and female patients.