The researchers are trying to evaluate a newer imaging technique (Ga-DOTATATE PET/CT) to see if it is more sensitive to localize the source of the hormone, which has caused the low phosphate levels.

Subjects will be contacted (phone script attached) to inform them of the study and the imaging modality. The first 10 patients that agree to participate in the study will be asked to present to the Mayo Clinic where they can provide a written consent and perform the imaging study.

Enrolled subjects will be evaluated in the clinical practice prior to having 68Ga-DOTATATE PET/CT imaging performed. The treating endocrinologist will be informed of the imaging results and will review the results with the subject using a follow-up visit or phone call; when a tumor is localized, the endocrinologist will discuss appropriate management options.

Subjects will be follow for one year post 68Ga-DOTATATE PET/CT.

Inclusion Criteria:

• Adults (18 years of age or older) seen at Mayo Clinic, Rochester for FGF23 mediated osteomalacia between 1/1/2000 and 1/30/2018 who provide informed consent to participate in the study.

Exclusion Criteria:

• Pregnant
• Prisoners
• Subjects diagnosed with heritable hypophosphatemic rickets/osteomalacia
• Subjects who do not consent for the study or withdraw consent during the duration of the study.
• Subjects in whom tumor localization and successful resection has already occurred.

Participants were monitored from administration of the radioactive imaging agent until approximately 30 minutes after PET/CT scan, for a total of approximately 2 hours.