The effect or oral
glucose ingestion on renal
phosphate reabsorption was studied in 13 patients with the inherited form of
vitamin D-resistant rickets (VDRR) and 5 normal subjects. In contrast to the normal subjects,
glycosuria developed in six VDRR patients after
glucose ingestion and resulted in a further 43% decrease in renal
phosphate reabsorption. This was accompanied by a 33% increase in
phosphate clearance. This was not attended by differences in fasting
glucose or
phosphorus levels between groups, or in their respective values 1 h after
glucose ingestion. Baseline renal
phosphate reabsorption was less and baseline
phosphate clearance was greater in those VDRR subjects who developed
glycosuria. The accumulated data suggest that excessive
glucose ingestion by some patients with VDRR may add an additional insult to the
phosphaturia characteristic of this disorder. This, in turn, would further compromise the response of circulating
phosphate to therapeutic attempts at oral
phosphate supplementation, thereby reducing the efficacy of oral
phosphate therapy on skeletal growth and development in this disorder.