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X-Linked Hypophosphatemia (XLH)

X-linked hypophosphatemia, is an X-linked dominant form of rickets that differs from most cases of rickets in that vitamin D supplementation does not cure


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331 - 2,979

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331 - 2,979

Europe Estimated

Age of Onset





Autosomal dominant


Autosomal recessive




X-linked dominant


X-linked recessive


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XLH, or X-linked hypophosphatemia, is a condition that affects bones, muscles, and teeth due to the excessive loss of phosphate. Phosphate is lost through the urine, which causes low levels of phosphorus in the blood, a condition called phosphate wasting or hypophosphatemia. Rickets is a hallmark of XLH and is caused by the softening of bones during growth in childhood. Rickets is a key feature of XLH in children and causes symptoms such as bowed legs.


5 Facts you should know



An inherited disorder characterized by low levels of phosphate in the blood.



Phosphate levels are low because phosphate is abnormally processed in the kidneys, which causes a loss of phosphate in the urine (phosphate wasting) and leads rickets.



XLH is usually diagnosed in childhood.



XLH is caused by mutations in the PHEX gene on the X chromosome, and inheritance is X-linked dominant.



Treatment generally involves supplements of phosphate and high-dose calcitriol and may also include growth hormones, corrective surgery, and dental treatment.

X-Linked Hypophosphatemia (XLH) is also known as...

X-Linked Hypophosphatemia (XLH)

X-linked hypophosphatemic rickets; XLH; Hypophosphatemic rickets, X-linked dominant; Hypophophatemia, X-linked; Vitamin D-Resistant Rickets, XPDR.

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X-Linked Hypophosphatemia (XLH) is also known as....

Common signs & symptoms

Abnormality of dental enamel

Abnormal tooth enamel
Enamel abnormalities
Enamel abnormality

Abnormality of the metaphysis

Abnormality of the wide portion of a long bone

Bone pain

Genu varum

Outward bow-leggedness
Outward bowing at knees


Low blood phosphate level

Joint dislocation

Joint dislocations
Recurrent joint dislocations


Softening of the bones

Rachitic rosary


Weak and soft bones

Tooth abscess

Current treatments

Burosumab (Brand name: Crysvita)

Manufactured by Ultragenyx Pharmaceutical, Inc.
FDA-approved indication: April 2018 approved for the treatment of X-linked hypophosphatemia (XLH) in adult and pediatric patients 1 year of age and older.

Top Clinical Trials

TitleDescriptionPhasesStatusInterventionsMore Information
Open Label Trial Assessing Safety and Efficacy of Burosumab (KRN23), in a Patient With ENS and Hypophosphatemic RicketsA 52 week, open label trial to assess the safety and efficacy of KRN23, an investigational antibody to FGF23, in a single pediatric patient with Epidermal Nevus Syndrome(ENS) and associated hypophosphatemic ricketsCompletedBiological: BurosumabPhase 3More Info
Effectiveness of Paricalcitol in Reducing Parathyroid Hormone (PTH) Levels in X-linked Hypophosphatemic RicketsThe purpose of this study is to determine the effectiveness of paricalcitol, a form of synthetic vitamin D, in lowering parathyroid hormone (PTH) levels and reducing disease symptoms in children and adults with X-linked hypophosphatemic (XLH) rickets.CompletedDrug: Paricalcitol|Other: PlaceboPhase 3More Info
Study of KRN23 in Adults With X-linked Hypophosphatemia (XLH)The primary efficacy objective of this study is to establish the effect of burosumab treatment compared with placebo on increasing serum phosphorus levels in adults with XLH.CompletedBiological: burosumab|Other: PlaceboPhase 3More Info
Open Label Study of KRN23 on Osteomalacia in Adults With X-linked Hypophosphatemia (XLH)The primary objective of this study is to establish the effect of KRN23 treatment on improvement in XLH-associated osteomalacia as determined by osteoid volume (osteoid volume/bone volume, OV/BV).CompletedBiological: burosumabPhase 3More Info
Efficacy and Safety of Burosumab (KRN23) Versus Oral Phosphate and Active Vitamin D Treatment in Pediatric Patients With X Linked Hypophosphatemia (XLH)The primary objective of this study is to evaluate the effect of KRN23 (burosumab) therapy in improving rickets in children with XLH compared with active control (oral phosphate/active vitamin D).CompletedBiological: burosumab|Drug: Oral Phosphate Supplement|Drug: active vitamin DPhase 3More Info
Evaluation of Safety, Tolerability, and Efficacy of INZ-701 in Adults With ENPP1 DeficiencyThe purpose of this study is to assess the safety and tolerability of INZ-701, an ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) enzyme replacement therapy, for the treatment of ENPP1 Deficiency (including Generalized Arterial Calcification of Infancy Type 1 [GACI] and Autosomal Recessive Hypophosphatemic Rickets Type 2 [ARHR2]).RecruitingDrug: INZ-701Phase 1|Phase 2More Info

Top Treatments in Research

AgentClass/Mechanism of ActionDevelopment StatusCompanyClinical StudiesMore Information
Drug: Paricalcitol|Other: Placebo Paricalcitol is a synthetic, biologically active vitamin D analog of calcitriol with modifications to the side chain (D2) and the A (19-nor) ring. Preclinical andin vitro studies have demonstrated that paricalcitol's biological actions are mediated through binding of the VDR, which results in the selective activation of vitamin D responsive pathways. Vitamin D and paricalcitol have been shown to reduce parathyroid hormone levels by inhibiting PTH synthesis and secretion.Phase 3Yale University|National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)Click here for clinical studiesMore Info
Drug: INZ-701Native ENPP1 is bound to the cell membrane with the active enzymatic portion of the protein outside the cell. We fused this domain with an antibody Fc fragment to construct INZ-701. In contrast from native ENPP1, INZ-701 is a soluble protein designed to circulate throughout the body and cleave extracellular ATP into PPi and AMP, a precursor of adenosine.Phase 1|Phase 2Inozyme PharmaClick here for clinical studiesMore Info

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