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Hypophosphatasia (/ ˌ h aɪ p oʊ ˈ f ɒ s f eɪ t ˌ eɪ ʒ ə /; also called deficiency of alkaline phosphatase, phosphoethanolaminuria, [5] or Rathbun's syndrome; [1] sometimes abbreviated HPP [6]) is a rare, and sometimes fatal, inherited [7] metabolic bone disease. [8]
Alkaline phosphatase levels are relatively low in those with Wilson's-related acute liver failure. [19] If neurological symptoms are seen, magnetic resonance imaging of the brain is usually performed; this shows hyperintensities in the part of the brain called the basal ganglia in the T2 setting. [14]
The enzyme alkaline phosphatase (ALP, alkaline phenyl phosphatase) is a phosphatase with the physiological role of dephosphorylating compounds. The enzyme is found across a multitude of organisms, prokaryotes and eukaryotes alike, with the same general function, but in different structural forms suitable to the environment they function in. Alkaline phosphatase is found in the periplasmic ...
Mutations in the ALPL gene lead to varying low activity of the enzyme tissue-nonspecific alkaline phosphatase (TNSALP) resulting in hypophosphatasia (HPP). [19] There are different clinical forms of HPP which can be inherited by an autosomal recessive trait or autosomal dominant trait, [16] the former causing more severe forms of the disease.
Laboratory findings include low-normal serum calcium, moderately low serum phosphate, elevated serum alkaline phosphatase, and low serum 1,25 dihydroxy-vitamin D levels, hyperphosphaturia, and no evidence of hyperparathyroidism. [8] Hypophosphatemia decreases 2,3-bisphosphoglycerate (2,3-BPG) causing a left shift in the oxyhemoglobin curve.
Alkaline phosphatase levels are usually high in hyperparathyroidism due to high bone turn over. In primary hyperparathyroidism, levels may remain within the normal range, but this is inappropriately normal given the increased levels of plasma calcium. [citation needed]
Hypophosphatasia is caused by a genetic defect of tissue-nonspecific alkaline phosphatase (TNSALP), an enzyme that plays a role in bone mineralization. Asfotase alfa is a recombinant glycoprotein that contains the catalytic domain (the active site) of TNSALP. It is thus a form of enzyme replacement therapy. [5] [12]
Low serum and urinary calcium; Low serum phosphate, except in cases of renal osteodystrophy; Elevated serum alkaline phosphatase (due to an increase in compensatory osteoblast activity) Elevated parathyroid hormone (due to low calcium) Furthermore, a technetium bone scan will show increased activity (also due to increased osteoblasts).