To collect information on the long-term effects of XLH on children and adults who have participated in burosumab clinical trials, adults and children who have not participated in burosumab clinical trials, and who may or may not have been treated with burosumab during the course of the study.
1) To determine if 5 doses of Epo (Erythropoietin) 1000 U/kg (birth weight) intravenous (IV) reduces the rate of death or neurodevelopmental impairment (mild, moderate, or severe) at 24 months of age.
2) To assess safety of Epo.
3) To determine whether Epo decreases the severity of HIE-induced brain injury as evidenced by early MRI and plasma biomarkers of brain injury.
