Hypophosphatemic Renal Rickets: Experience in 10 Years

Abstract

Objetives: Analyze frequency of X- linked renal hypophosphatemic rickets (XLH) in the period of 10 years, determine clinical, laboratory and radiological finding, analyze the height Z score DS (HSDS) at diagnostic and follow up and analyze the efficacy of therapy in the longitudinal growth in relation to age and at the starting of the treatment.

Methods: This is a retrospective, observational and longitudinal study in patient with X- linked renal hypophosphatemic rickets, which were seen, in the Nephrology Service of the Instituto Nacional de Salud del Niño (INSN) in Lima, during the years 2002-2011. We used the Microsoft Office Excel 2007 program, NCHS 2007 table and WHO Anthro 2009 for the calculation of Z score size. Results: In 123 outpatients in the INSN with diagnosis of rickets, 22 (18%) were XLH based on clinical, laboratory and radiologicical criteria, of those, 82% were girls and 73% pre-school. The average age at onset was 1.8 years and at diagnosis (1st query) was 4.3 years. Four (18%) came from provinces and 55% had a familiar history. There were lower limb deformity, statural delay by more than 70%, gait disturbance 50% and a lower percentage of epiphyseal enlargement, raquitic rosary and diminished of muscle strength. All of them had hypophosphatemia and high level of alkaline phosphatase. In 10 cases it was performed dosage of parathyroid hormone, which was normal, but active vitamin D was diminished. Hyperphosphaturia was observed in urine, with calciuriawasnormal.In19patientswecalculated phosphate tubular reabsorption percentage, which was diminished. HSDS analysis results can be grouped in 3 series: a) Z Score>-1.88 in six patients, b) Z Score< -1.88 under 6years in 7patients, c) Z Score < -1.88 over 6 years sin three patients. In group(a) there was a greater commitment to final height in those with irregular therapy. In group (b) 3 from 7 patients, the final Z score was profoundly impaired in those with irregular therapy. In group(c) despite its late start of treatment, there is aslight improvement in final height, since all therapy was met regularly, but did not reach the normal growth. 73% of the patients received phosphate salts, 12 patients took calcitriol and 27% diuretics. There was bone rarefaction in 100% of the X-ray performed cases; diminished bone age was seen in 64% and nephrocalcinosis in 5 cases.

Conclusions: The XLH is a major cause of growth retardation, there may be the sporadically form in a significant percentage, nephrocalcinosis is a common complication and there is a higher incidence in women because of X-linked inheritance.