In this patient...

  • 25-OH-D level = 63 ng/mL (normal 20-60)
  • 24,25-(OH)2D level = 0.4 ng/mL (normal 2-8)
  • Thus, 25-OH-D:24,25 OH D = 125 (normal 15-25)

    • Diagnosis

  • Likely Genetic defect in vitamin D 24 hydroxylase gene
    24 hydroxylase is responsible for degradation of active vitamin D to inactive metabolite
    24,25-OH vitamin D

  • The diagnosis can be confirmed by genetic testing

    • References

  • A lifetime of hypercalcemia and hypercalciuria, finally explained.JCEM2014 Mar;99(3):708-12
  • Loss-of-function mutations of CYP24A1, the vitamin D 24-hydroxylase gene, cause long-standing hypercalciuric nephrolithiasis and nephrocalcinosis. J.Urol 2013 Aug;190(2):552-7