Autosomal recessive hypophosphatemic rickets type 2 (ARHR2) due to ENPP1-deficiency.

Awareness for hypophosphatemic rickets has increased in the last years, based on the availability of specific medical treatments. Autosomal recessive hypophosphatemic rickets type 2 (ARHR2) is a rare form of hypophosphatemic rickets, which is known to develop in survivors of generalized arterial calcification of infancy (GACI). Both disorders are based on a deficiency of ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) and present with a high clinical variability and a lack of a phenotype-genotype association. ARHR2 is characterized by phosphate wasting due to elevated fibroblast growth factor 23 (FGF23) levels and might represent a response of the organism to minimize ectopic calcification in individuals with ENPP1-deficiency. This report reviews the recent clinical and preclinical data on this ultra-rare disease in childhood. • Deficiency of ENPP1 is associated GACI and ARHR2. • GACI and ARHR2 are recognized as two distinct clinical phenotypes which manifest at different ages. • ARHR2 is associated with elevated levels of FGF23, however FGF23-targeted treatments might increase the risk for ectopic calcification. [ABSTRACT FROM AUTHOR]