Activity of renal 25-hydroxyvitamin D3-1 alpha-hydroxylase in a case of X-linked hypophosphataemic rickets.
In 1974, a 2-year-old boy was diagnosed as having X-linked hypophosphataemic rickets (XLH) because of severe rickets and hypophosphataemia. The vitamin D metabolite concentrations, blood and urine chemistry and renal 25-hydroxyvitamin D3 (25OHD3)-1 alpha-hydroxylase were measured in 1982 (about 2 weeks after withdrawal of medication). 1 alpha-hydroxylase was 392 pg/mg tissue/20 min in the patient, which was high compared with aged-matched controls (69.7 +/- 28.5 pg/mg tissue/20 min, mean +/- SD, n = 7). Our present studies showed that the 1 alpha-hydroxylase activity in the patient with XLH was elevated. Therefore, the normal or low 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) concentrations in XLH patients could be due to accelerated catabolism of 1,25-(OH)2D3 or abnormally regulated 25OHD3-1 alpha-hydroxylase in response to hypophosphataemia, although significantly elevated above that in normal controls.
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002675:Child, Preschool; D006801:Humans; D007015:Hypophosphatemia, Familial / Q000150:complications / Q000201:enzymology*; D007668:Kidney / Q000201:enzymology*; D008297:Male; D012279:Rickets / Q000150:complications / Q000201:enzymology*; D013250:Steroid Hydroxylases / Q000378:metabolism*
D013250:Steroid Hydroxylases; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase