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Vitamin D metabolism in hypophosphatasia
Insights
This study tracked a boy with infantile hypophosphatasia, observing vitamin D metabolite changes. Vitamin D treatment corrected rickets and normalized alkaline phosphatase levels.
Area of Science:
- Biochemistry
- Pediatrics
- Endocrinology
Background:
- Hypophosphatasia is a rare genetic disorder affecting bone mineralization.
- Infantile hypophosphatasia presents with severe skeletal abnormalities and metabolic derangements.
Observation:
- A 4-month-old boy with infantile hypophosphatasia exhibited hypercalcemia and altered vitamin D metabolites.
- The patient later developed vitamin D-deficiency rickets due to restricted intake and sun exposure.
- Serum alkaline phosphatase was initially low, rose during rickets, and normalized with treatment.
Findings:
- During hypercalcemia, 25-hydroxyvitamin D was normal, with low 1,25-(OH)2D and high other dihydroxymetabolites.
- Vitamin D deficiency led to very low 25-hydroxyvitamin D and increased urinary cyclic AMP.
- Vitamin D therapy significantly increased 1,25-(OH)2D levels.
Implications:
- This case highlights the complex interplay between hypophosphatasia and vitamin D metabolism.
- Understanding these metabolic shifts is crucial for managing rickets in infants.
- Effective vitamin D supplementation can reverse rickets and normalize biochemical markers.
Abstract:
A 4-month-old boy with the infantile form of hypophosphatasia was followed for 9 months with measurements of serum calcium, phosphate, alkaline phosphatase and various vitamin D metabolites, together with urinary excretion of cyclic AMP. During the initial hypercalcemic stage the serum concentration of 25-hydroxyvitamin D was normal. Urinary cyclic AMP was low and the serum concentration of the dihydroxymetabolites of vitamin D were appropriate to the high serum calcium with low 1,25-(OH)2D and relatively high 24,25(OH)2D and 25,26(OH)2D levels. Due to restrictions of the vitamin D intake and lack of exposure to sun he developed vitamin D-deficiency rickets at 9 months of age with very low serum concentration of 25-hydroxyvitamin D and markedly increased urinary excretion of cyclic AMP. Following vitamin D treatment the serum level of 1,25(OH)2D showed a brisk rise to a considerably elevated value. Initially the serum concentration of alkaline phosphatase was well below the normal range, rose markedly during the stage of active rickets and returned to the characteristic low levels of hypophosphatasia with healing of the rickets.