Endocrine Abstracts

Introduction: The biochemical diagnosis of hypophosphataemic rickets relies on measurement of tubular phosphate reabsorption. However, as the renal tubules are immature at birth and the reference range for urine phosphate excretion is not well defined in young children, there is uncertainty about how early in life a biochemical diagnosis of phosphate wasting can be made. In addition, the benefit of early treatment of hypophosphataemic rickets is unclear.

History: We recently managed 2 infants born to a mother with hypophosphataemic rickets. In March 2001, she delivered a healthy baby boy at full-term. On the parents’ request he was tested at 6 weeks. The biochemical abnormalities were confirmed at 12 weeks and he was treated with phosphate and 1 alpha calcidol syrup. He walked at the age of 11 months but by the age of 1 year showed marked anterior bowing of the femurs, exaggerated lumbar lordosis and genu varum. The skeletal deformities have progressed despite treatment. In June 2004, the mother had a baby girl. At 10 weeks of age her biochemistry showed evidence of tubular phosphate wasting. Treatment was started at six months old, but despite this she also has leg deformity at the age of 1 year.

Investigation:

Discussion: The repeated early measurement of alkaline phosphatase and renal phosphate handling (%TRP and TmP/GFR) allowed early diagnosis in these children. This illustrates that the tubular phosphate wasting in hypophosphataemic rickets can be evident as early as 6 weeks of life. There is little evidence that very early treatment in these patients improves outcome and this has implications for managing parents’ expectations.