Updated: 10/10/2016

Hypophosphatasia

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Introduction
  • Metabolic bone disease characterized by a generalized impairment of bone mineralization 
  • Incidence
    • estimated to be 1 in 100,000
  • Pathophysiology
    • low levels of alkaline phosphate result in decreased synthesis of inorganic phosphate necessary for bone matrix formation
    • osteoid that forms in the hypertrophic zone of the growth plate fails to mineralize
    • the zone of provisional calcification never forms and growth is inhibited
  • Genetics
    • inheritance pattern
      • autosomal recessive 
    • caused by a mutation in the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP) 
  • Associated conditions
    • orthopaedic manifestations
      • similar to rickets
      • bow legs
      • short stature
    • non-orthopaedic manifestations
      • abnormal tooth formation
      • loss of teeth
Presentation
  • Clinical findings 
    • presentation similar to rickets 
      • genu varum
      • short stature
    • abnormal dentition 
Imaging
  • Radiographs
    • recommended
      • AP and lateral of affected bone
    • findings
      • abnormal bone formation
        • "deossification of bone" adjacent to growth plate 
        • physeal widening
Evaluation
  • Labs
    • serum
      • decreased serum alkaline phosphatase 
    • urine
      • phosphoethanolamine in the urine diagnostic for hypophosphatasia
 
Treatment
  • Nonoperative
    • no approved therapies
      • phosphate therapy under investigation but not utilized at this time
 

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Questions (5)
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(OBQ08.38) Hypophosphatasia is associated with which of the following laboratory findings? Review Topic

QID: 424
1

Hyperbilirubinemia

1%

(12/1418)

2

Decreased urinary phosphoethanolamine

4%

(58/1418)

3

Decreased urinary inorganic pyrophosphate

4%

(62/1418)

4

Decreased serum phosphate

38%

(535/1418)

5

Decreased serum alkaline phosphatase

52%

(743/1418)

ML 4

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