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

Autosomal recessive hypophosphatemic rickets (ARHR) type 2 (ARHR2) is a rare form of hypophosphatemic rickets (HR) caused by a 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 one year. Laboratory tests revealed elevated fibroblast growth factor 23 level, hypophosphatemia, and 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 ENPP1. 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 three years. No evidence of generalized arterial calcification was apparent during follow-up, and growth rate was satisfactory.