Experimental drug aims to fix Bone-Weakening phosphate problem in rare disease

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

* INCLUSION CRITERIA: In order to be eligible to participate in this study, an individual must meet all of the following criteria: * Confirmed diagnosis of fibrous dysplasia * Serum phosphate \<10th percentile for age and sex, AND intact serum FGF23 \>=30 pg/mL * Age \>=1 year * Provision of signed and dated informed consent/assent form * Stated willingness of subject or Legally Authorized Representative (LAR) to comply with all study procedures and availability for the duration of the study * For females of reproductive potential: agreement to use highly effective contraception for during study participation. Highly effective contraception methods include: * Total abstinence (when this is in line with the preferred and usual lifestyle of the participant). Periodic abstinence (e.g., calendar, ovulation, symptothermal, postovulation methods) and withdrawal are not acceptable methods of contraception * Female sterilization (have had surgical bilateral oophorectomy with or without hysterectomy) or tubal ligation at least six weeks before taking study treatment. * Male sterilization (at least 6 months prior to screening). For female participants on the study the vasectomized male partner should be the sole partner for that participant. * Combination of the following (a+b or a+c, or b+c): * Use of oral, injected or implanted hormonal methods of contraception or other forms of hormonal contraception that have comparable efficacy (failure rate \<1%), for example hormone vaginal ring or transdermal hormone contraception * Placement of an intrauterine device (IUD) or intrauterine system (IUS) * Barrier methods of contraception: Condom or Occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/vaginal suppository * For males of reproductive potential: use of condoms or other methods described above to ensure effective contraception with partner * Minimum body weight of 7.5 kilograms EXCLUSION CRITERIA: An individual who meets any of the following criteria will be excluded from participation in this study: * Pregnancy or lactation * Known allergic reactions to burosumab or drug component * Treatment with another investigational drug within 30 days of screening * Treatment with burosumab within 30 days of screening * Have any condition which in the opinion of the PI could present a concern for subject safety or difficulty with data interpretation * Severe renal impairment or end stage renal disease, defined as: pediatric patients with estimated glomerular filtration rate (eGFR) 15 mL/min/1.73m2 to 29 mL/min/1.73m2 or end stage renal disease (eGFR \< 15 mL/min/1.73m2), adult patients with creatinine clearance (CLcr) 15 mL/min to 29 mL/min or end stage renal disease (CLcr \< 15 mL/min)