Abstract
Red cell inorganic phosphate (Pi) was studied in two siblings (a 3y-old girl and a 2m-old boy) with VDDR and another infant (2m-old boy) with RTA before and during therapy. The girl was already on 2μg 1αOHD3/d which was discontinued and the boy was followed from the age of two months. In both cases the parameters studied were normal at start and were followed regularly until SeCa had fallen respectively to 6.52 and 6.38mg/dl, when 1αOHD3 administration commenced. At that time plasma Pi (PlPi) also fell by 1-1.5mg/dl while red cell Pi (RBCPi) hardly changed. Consequently the distribution of phosphate ions across the erythrocyte membrane changed markedly. All parameters studied started normalising from the first weeks of treatment. In the case of RTA at the time of diagnosis when blood pH was 7.27, HCO3− 6mEq/1 and C1− 118mEq/1 SeCa was 8.5mg/dl, PlPi 4.6mg/dl and RBCPi abnormally low (0.7mg/dl). After the commencement of HCO3−, SeCa started rising while PlPi showed a transient fall and began rising after a week when 1αOHD3 (0.3μg/d) and citrate were given. RBCPi showed a steady rise and within 2 months it had reached physiological levels (2.8mg/dl). At that time SeCa was 9.8mg/dl and PlPi 5.7mg/dl. Metabolic acidosis seems to be responsible for the depletion of erythrocyte Pi and probably in other cells too, while the correction of pH leads to repletion even before HCO3− and Cl− ion concentrations normalise.
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Lapatsanis, P., Vrionis, G., Salvanos, H. et al. INTRACELLULAR PHOSPHATE METABOLISM IN METABOLIC DISORDERS: Vitamin D dependent rickets (VDDR) and renal tubular acidosis (RTA). Case reports. Pediatr Res 19, 1117 (1985). https://doi.org/10.1203/00006450-198510000-00269
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DOI: https://doi.org/10.1203/00006450-198510000-00269