Updated: 6/18/2021

Hypophosphatasia

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  • summary
    • Hypophosphatasia is a metabolic bone disease caused by a mutation in the isoenzyme of alkaline phosphatase that leads to low levels of alkaline phosphate and generalized impairment of bone mineralization. Patients present with clinical manifestations similar to rickets with bow legs, short stature, abnormal teeth, and increased susceptibility to fractures. 
    • Diagnosis is made with the presence of phosphoethanolamine in the urine.
    • Treatment modalities are currently under investigation.
  • Epidemiology
    • Incidence
      • estimated to be 1 in 100,000
  • Etiology
    • 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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(OBQ11.160) A decrease in alkaline phosphatase would most likely be manifest in which metabolic disorder?

QID: 3583
1

Familial hypocalciuric hypercalcemia

16%

(471/3010)

2

Hypophosphatasia

49%

(1473/3010)

3

X-linked hypophosphatemia

18%

(528/3010)

4

Secondary hyperparathyroidism

13%

(398/3010)

5

Tertiary hyperparathyroidism

4%

(109/3010)

L 4 C

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

QID: 424
1

Hyperbilirubinemia

1%

(13/1617)

2

Decreased urinary phosphoethanolamine

4%

(67/1617)

3

Decreased urinary inorganic pyrophosphate

5%

(73/1617)

4

Decreased serum phosphate

38%

(616/1617)

5

Decreased serum alkaline phosphatase

52%

(840/1617)

L 4 D

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(SAE07PE.23) Figure 11 shows the radiograph of a 2-year-old child with marked genu varum and tibial bowing. Based on these findings, what is the best initial course of action?

QID: 6083
FIGURES:
1

Obtain serum phosphorous, calcium, and alkaline phosphatase levels.

82%

(358/435)

2

Obtain a scanogram to assess for limb-length discrepancy.

1%

(3/435)

3

Perform bilateral valgus osteotomies to correct the deformities.

1%

(3/435)

4

Measure the child for a varus prevention orthosis.

5%

(20/435)

5

Educate the family about physiologic genu varum and conduct a follow-up examination in 6 months.

10%

(45/435)

L 2 E

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