An uncommon cause of hypophosphatemic rickets: Questions

Excerpt

A 4-and-a-half-year-old boy, who had been followed up with a diagnosis of hypophosphatemic rickets at a local hospital, was referred to our clinic. He was admitted with growth retardation and bowing of legs when he was 11 months old and was given oral phosphate and calcitriol therapies. His motor development was normal until 10 months of age, but he began to walk at 30 months of age. He had polyuria and polydipsia since 2 years of age. There was no consanguinity between his parents; none of the family members had any kidney disease. He had two healthy brothers and one healthy sister. His height was 101 cm (10–25 p) and weight 17.5 kg (50–75 p). Physical examination was unremarkable. The results of laboratory examinations were as follows: blood urea nitrogen 16 mg/dL, serum creatinine 0.44 mg/dL, serum uric acid 2.1 mg/dL, sodium 140 mEq/L, potassium 4.4 mEq/L, chloride 105 mEq/L, calcium 9.4 mg/dL, phosphorus 3.5 mg/dL (he was on oral phosphate therapy), magnesium 2.4 mg/dL, plasma glucose 72 mg/dL, ALT 16 U/L and AST 40 U/L. pH was 7.31, and bicarbonate was 16.3 mmol/L. On urinalysis pH 7, density 1010, protein trace, glucose 2 + . Urine sodium 73 mEq/L, potassium 58 mEq/L, chloride 69 mEq/L, urine protein/creatinine ratio 0.88 (mg/mg) (Table 1). Daily calcium excretion was 11.9 mg/kg/d and protein excretion 12 mg/m²/h. Tubular phosphate reabsorption (TPR) was calculated as 83% (N > 85%). Urine aminoacid analysis yielded generalized aminoaciduria. On ultrasonography, medullary nephrocalcinosis and increased echogenicity of both kidneys were detected. Ophthalmological examination was normal. A urine organic acid analysis showed normal succinyl acetone levels. Leukocyte cystine level was within normal limits. Ceruloplasmin and urinary copper excretion was also normal. …