X-Linked Hypophosphatemia Caused by a New Partial Insertion of LINE-1 in the PHEX Gene.

X-linked hypophosphatemia (XLH), primarily caused by mutations of the PHEX gene, is the most common cause of genetic rickets. Pediatric cases of XLH typically present with elevated levels of serum fibroblast growth factor 23 (FGF23), hypophosphatemia, rickets, and impaired growth. Here, we report a 2-year-old boy diagnosed with XLH, presenting with short stature, genu varum, and hypophosphatemia. Sanger sequencing revealed a novel mutation of the PHEX gene, comprising a 62-bp poly-T and a 421-bp long interspersed element-1 (LINE-1) insertion into exon 22, which appears to induce the hypophosphatemia. This study presents the first documented case of XLH associated with a partial LINE-1 insertion in PHEX. We suggest that LINE-1 transposon element insertions be considered in XLH patients lacking other known mutations.