Hearing Loss Is Part of the Clinical Picture of ENPP1 Loss of Function Mutation

Background: Ecto/nucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1) loss-of-function mutations have been described in patients with autosomal recessive hypophosphatemic rickets (HR), in patients with generalized arterial calcification of infancy (GACI) and in several patients with both conditions. Out of more than 50 cases of homozygous or compound heterozygous ENPP1 loss-of-function mutations published so far, 1 case with labyrinthine deafness probably due to occlusion of inner ear supplying arteries and 2 cases of conductive hearing loss due to stapedovestibular calcification diagnosed in childhood have been reported. Aims: To report a case of ENPP1 loss-of-function novel mutation presenting with HR and very early onset and severe hearing loss. Methods: Case report and review of the literature. Results: We report on a patient homozygous for a novel 1-bp deletion in ENPP1 that presented with GACI evolving towards HR associated with a mixed hearing loss (both labyrinthine and conductive) diagnosed at 9 days of life that evolved towards profound labyrinthine deafness. Conclusion: Hearing loss is a rare finding in patients with ENPP1 loss-of-function mutations. Interestingly, it has already been described in other affected patients, in ENPP1 knock-out mice and in other diseases of pyrophosphate metabolism. Conversely it seems to be absent in children with the X-linked form of HR. (C) 2013 S. Karger AG, Basel