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X-linked hypophosphatemia
Pathology:
1) reduced proximal tubular resorption of phosphate
2) increased fractional excretion of phosphate
3) osteomalacia develops in adult life
4) overgrowth of bones at sites of muscular tendon attachment may compress nerves or limit movement
5) increased secretion of FGF-23
Epidemiology:
- bony abnormalities are less common in women
Genetics:
- X-linked inheritance
Clinical manifestations:
1) patients may be asymptomatic
2) short stature, rachitic bones
3) recurrent striss fractures
4) dental abscesses
5) legs are particularly short & deformed
6) bone age & dentition are retarded
7) skull becomes deformed
- maxillofacial region may be abnormal
Laboratory:
1) serum chemistries
a) serum phosphorus: hypophosphatemia
b) alkaline phosphatase in serum is elevated
c) serum parathyroid hormone (PTH) is normal or high
d) serum calcium is normal
2) urine chemistries
a) urine calcium: Ca+2 excretion is normal or low
b) glycine in urine: mild glycinuria
c) glucose in urine: glycosuria may occur
Management:
1) phosphate (NutraPhos) 1-4 g/day in divided doses
2) calcitriol or some other form of vitamin D
3) burosumab improves renal tubular phosphate reabsorption, serum phosphorus levels, linear growth, & physical function & reduces pain & severity of rickets [2]
3) orthopedic management
-> delay corrective surgery until active growth phase is complete (exception is genu valgum {knock knee})
General
genetic disease of bone/skeletal system
hypophosphatemia
Database Correlations
OMIM 307800
References
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1328
- Carpenter TO, Whyte MP, Imel EA
Burosumab Therapy in Children with X-Linked Hypophosphatemia.
N Engl J Med 2018; 378:1987-1998. May 24, 2018
PMID: 29791829
https://www.nejm.org/doi/full/10.1056/NEJMoa1714641