Research Progress in Pseudoxanthoma Elasticum and Related Ectopic Mineralization Disorders

Heritable ectopic mineralization disorders represent a phenotypically diverse group of conditions characterized by deposition of calcium phosphate complexes in soft connective tissues. The prototype of such conditions is pseudoxanthoma elasticum (PXE), and related conditions with overlapping clinical features include generalized arterial calcification of infancy (GACI) and arterial calcification due to CD73 deficiency (ACDC). Molecular genetic investigations have revealed mutations in the genes physiologically involved in generation of inorganic pyrophosphate (PPi) and phosphate (Pi), and the findings suggest a unifying pathomechanism relating to reduced PPi/Pi ratio. This hypothesis is based on the notion that PPi serves as a powerful inhibitor of mineralization while Pi is a pro-mineralization factor, and an appropriate PPi/Pi ratio is critical for prevention of ectopic mineralization under homeostatic conditions. PXE International, the premiere patient support organization, advocating on behalf of patients and families with PXE, sponsors regular research meetings evaluating the progress in this and related ectopic mineralization disorders. The latest meetings were held in September 2014 in Bethesda, MD and in September 2015 in Budapest, Hungary. This report summarizes the latest progress in research on PXE and related ectopic mineralization disorders, based on presentations and discussions in these meetings, with pharmacologic implications for currently intractable disorders.