Connect with a community of support for
X-linked hypophosphatemia (XLH)
XLH Network
The XLH Network is a global patient support organization for people with XLH, parents, and caregivers. The website contains educational resources about XLH for patients and medical professionals.
NIH Genetic and Rare Diseases Information Center (GARD)
GARD maintains a list of rare diseases and related terms to help people find reliable information about their disease.
National Organization for Rare Disorders (NORD)
NORD is a patient advocacy organization dedicated to individuals with rare diseases and the organizations that serve them.
CRYSVITA Start Guide
This step-by-step guide provides information for initiating, dosing, and administering CRYSVITA as well as guidance for patients and caregivers.
UltraCare Start Form
Download and complete the UltraCare Start Form with your patient.
CRYSVITA Proposed Mechanism of Action Video
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Glossary
antibody
A protein that is made by the immune system or a protein that is modified in a lab to recognize and block a target that threatens the body’s normal function.
baseline
The beginning of the study before patients are given any treatment.
bone histomorphometry
A method of assessing bone quality from bone biopsy samples. Histomorphometry includes assessments of osteoid volume to bone volume, osteoid thickness, and mineralization lag times.
fibroblast growth factor 23 (FGF23)
A protein that plays a role in phosphate homeostasis. In XLH, the excess circulating FGF23 leads to increased signaling, resulting in impaired phosphate uptake.
least squares (LS) mean
A statistic for the estimate of the mean after adjusting for the effect of other variables in a study.
mineralization
A process where minerals like phosphorus are deposited in the bone, causing the bone to harden.
mineralization lag time (MLt)
The interval between osteoid formation and osteoid mineralization. In XLH, mineralization lag times are long, pointing to abnormalities in the process of bone mineralization.
osteoid
The bone matrix; an unmineralized component of bone.
osteoid thickness (O.Th)
A measurement of the amount of unmineralized bone.
osteoid volume to bone volume (OV/BV)
A ratio of unmineralized bone to mineralized bone. In XLH, this ratio is large, pointing to a greater presence of unmineralized bone.
osteomalacia
A softening and weakening of the bones in adults caused by deficiencies in vitamin D, calcium, or phosphate. In children, osteomalacia can occur simultaneously with rickets.
phosphorus
A mineral that is important for proper bone development and repair.
physical function
Activities associated with independent movement, such as walking, standing, bending, getting into or out of a car, etc.
placebo
In Study 4 of adults with XLH, placebo refers to a saline injection.
Radiographic Global Impression of Change (RGI-C)
A way to measure the extent of the healing of rickets. This score uses a 7-point scale to rank the healing of rickets and can range from -3=severe worsening to 0=no change to +3=near/complete healing. An RGI-C global score of +2.0 means a substantial healing of rickets was achieved after treatment. This score is complementary to RSS.
rickets
A softening and weakening of the bones in children caused by deficiencies in vitamin D, calcium, or phosphate. In adulthood, after the growth plates have fused, rickets continues as osteomalacia.
serum phosphorus
Amount of phosphorus in the blood.
Thacher Rickets Severity Score (RSS)
A way to measure changes in the severity of rickets. This score uses a 10-point scale to rank the severity of rickets from 0 (normal) to 10 points (severe). A lower score means reduced severity of rickets. This score is complementary to RGI-C.
Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)
A 24-item patient-reported questionnaire originally developed for use in clinical trials in patients with hip and/or knee osteoarthritis. Higher scores on WOMAC indicate worsening within pain, stiffness, and physical function dimensions.