Autosomal Recessive Hypophosphatemic Rickets Type 2 Associated with a Novel ENPP1 Variant in a Taiwanese Girl

Autosomal recessive hypophosphatemic rickets (HR) type 2 (ARHR2) is a rare form of HR caused by variant of the gene encoding ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). Our patient presented with a history of unsteady gait and progressively bowing legs that had commenced at the age of 1 year. Laboratory tests revealed an elevated level of fibroblast growth factor 23 (FGF23), hypophosphatemia, and a high urine phosphate level. Radiography revealed the typical features of rickets. Next-generation sequencing identified a previously reported c.783C>G (p.Tyr261Ter) and a novel c.1092-42A>G variant in the ENPP1 gene. The patient was prescribed oral phosphates and active vitamin D and underwent guided growth of both distal femora and proximal tibiae commencing at the age of 3 years. No evidence of generalized arterial calcification was apparent during follow-up, and growth rate was satisfactory.