A Natural History Study of Patients With Generalized Arterial Calcification of Infancy (GACI) or Autosomal Recessive Hypophosphatemic Rickets Type 2 (ARHR2)

This is a natural history study of patients with Generalized Arterial Calcification of Infancy (GACI) or Autosomal Recessive Hypophosphatemic Rickets Type 2 (ARHR2).

GACI is an ultra-rare disorder with an estimated birth prevalence of around 1 in 200,000. GACI is characterized by extensive arterial calcifications, arterial stenosis, myointimal proliferation and periarticular calcifications. Individuals with GACI also experience calcification in other body areas, such as joints and parenchymal organs.

GACI is generally fatal before birth or within the first six months after birth. The cause of death is frequently myocardial infarction or stroke, and hypertension and congestive heart failure are common in fetuses and infants with GACI. The first six months of life are considered a critical period for GACI patients, and approximately 85% of infants with GACI do not survive beyond this period (Moran 1975). However, the mortality rate decreases substantially among patients who do survive beyond the critical period. Reports exist of patients with GACI who survived into adulthood, but the frequency of this occurrence is unknown, and adult patients suffer from a number of sequelae such as cognitive impairment related to stroke. ARHR2 is characterized by short stature, dental caries, and bone deformities, and biochemically by hypophosphatemia, hyperphosphaturia and elevated plasma alkaline phosphatase. The disease frequency is unknown.

GACI and ARHR2 are most commonly due to mutations of ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1), or less often from mutations in ABCC6 (adenosine triphosphate binding cassette transporter protein subfamily C member 6). No founder mutations are known, and thus no ethnic predilection is known. Both the GACI and ARHR2 phenotypes are potentially fatal or associated with severe morbidity, with no FDA-approved drugs or proven treatments. Animal data suggest that enzyme replacement therapy with ENPP1-Fc may be effective in preventing morbidity or mortality of GACI and ARHR2.

PXE (pseudoxanthoma elasticum) is an autosomal recessive disorder due to mutations in ABCC6 or, less often, ENPP1. PXE is characterized by ectopic calcification of the skin, eyes, cardiovascular system and gastrointestinal system. This study will not focus on PXE but will collect data on PXE patients, particularly when their presentation suggests elements of the GACI or ARHR2 phenotypes.