Rare tubulopathy - primary hypophosphatemic rickets (case report)

Primary hypophosphatemic rickets is a rare disorder caused by inborn defect of renal tubular reabsorbtion and usually manifested in childhood and infancy with stunted growth and deformities of lower limbs. Patient 12 years old, female, was born to healthy parents, at 41 weeks of gestation by normal delivery and had a normal birth weight and length. She had one healthy sibling (male). Psychomotor development until the age of 2 years was normal. Since the age of 2 years deformation of legs and difficulties with walking have been observed. The Patient was consulted by Pediatric Orthopedist, Nephrologists and Endocrinologist. The blood biochemical findings revealed normal pH, normal calcium (CA), potassium (K), sodium (Na) concentrations, very low phosphate (P) with markedly elevated alkaline phosphatase (AP) and slightly elevated parathyroid hormone (PTH) concentration; urine test indicated impaired tubular function: mild glucosuria, proteinuria, and markedly increased phosphaturia. Phosphate tubular reabsorbtion (PTR) was 52%, phosphate/creatinine clearance 0,52, renal threshold phosphate concentration (TmP/GFR) 0,25 mmol/l. Genetic tests results not available yet.

the diagnosis of phosphate diabetes made on the basis of clinical-laboratory data. The therapy with Inorganic phosphate (50-100mg/kg/d) and 1,25(OH)D3 40-50 ng/kg/d had been started. Childs walking abilities improved with treatment, the deformation of legs decreased, but O-legs and other skeletal deformations are still remarkable. Auxological parameters are not satisfactory. Physical growth is below the normal range (height SDS -3,78); the patient's predicted height less than target height. Biochemical monitoring performed regularly under the treatment, serum phosphate remains below normal, serum ALP is still elevated.

This case is in line with other publications and indicates the difficulty to achieve normal phosphate levels and normal growth without an additional treatment with growth hormone. At this stage of the disease, the question of referring to the growth hormone therapy is being considered aimed to improve the growth tendencies. It is possible that orthopedic surgery is also needed in the future.