Sir.—I read with interest the article by Klein et al entitled "Infantile Vitamin D-Resistant Rickets Associated With Total Parenteral Nutrition" (TPN) (Journal 1982;136:74-76). The cases of rickets in those three infants were most likely of different pathogeneses, but related to deficiency of some vitamin D metabolite or metabolites.
Although the low level of phosphorus (3.8 mg/dL) of the first case might be responsible for the development of rickets, a more important observation was that five months after supplementation with vitamin D, the child's serum level of 1,25-dihydroxyvitamin
D (1,25-[OH]2-D) was found to be very low (3 pg/mL). In the second case, serum calcium and phosphorus levels were normal and the initial level of 25-hydroxyvitamin D (25-OH-D) could be accepted as low normal (11 ng/mL) for a malnourished infant.1 His serum level of immunoreactive parathyroid hormone (iPTH) was not elevated despite the presence of rickets (which might be due
OZSOYLU S. Rickets and Deficiency of Vitamin D Metabolites. Am J Dis Child. 1982;136(8):754. doi:10.1001/archpedi.1982.03970440098035