Effects of therapy in X-linked hypophosphatemic rickets

Adverse renal and metabolic effects associated with oral sodium phosphate bowel preparation

Colorectal cancer can be prevented by the removal of adenomatous polyps during screening colonoscopy, but adequate bowel preparation is required. Oral sodium phosphate (OSP), an effective bowel purgative, is available over the counter and requires a substantially lower volume than polyethylene glycol-based preparative agents. Accumulating reports implicate OSP in electrolyte disturbances as well as acute kidney injury (AKI) in a syndrome termed phosphate nephropathy (a form of nephrocalcinosis). Despite published case reports and case series, the actual incidence, risk factors, and natural history of phosphate nephropathy remain largely undefined. Several recent observational studies have provided new information on these important issues while supporting a link between OSP and acute phosphate nephropathy as well as the development of chronic kidney disease in elderly patients, many of whom had a normal serum creatinine at the time of OSP ingestion. This review summarizes current knowledge about the renal complications of OSP, risk factors for its development, and the pathophysiology of acute and chronic kidney damage in nephrocalcinosis.

[Inherited monogenic kidney stone diseases: recent diagnostic and therapeutic advances]

Hereditary monogenic kidney stone diseases are rare diseases, since they account for nearly 2% of nephrolithiasis cases in adults and 10% in children. Most of them are severe, because they frequently are associated with nephrocalcinosis and lead to progressive impairment of renal function unless an early and appropriate etiologic treatment is instituted. Unfortunately, treatment is often lacking or started too late since they are often misdiagnosed or overlooked. The present review reports the genotypic and phenotypic characteristics of monogenic nephrolithiases, with special emphasis on the recent advances in the field of diagnosis and therapeutics. Monogenic stone diseases will be classified into three groups according to their mechanism: (1) inborn errors of the metabolism of oxalate (primary hyperoxalurias), uric acid (hereditary hyperuricemias) or other purines (2,8-dihydroxyadeninuria), which, in addition to stone formation, result in crystal deposition in the renal parenchyma; (2) congenital tubulopathies affecting the convoluted proximal tubule (such as Dent's disease, Lowe syndrome or hypophosphatemic rickets), the thick ascending limb of Henlé's loop (such as familial hypomagnesemia and Bartter's syndromes) or the distal past of the nephron (congenital distal tubular acidosis with or without hearing loss), which are frequently associated with nephrocalcinosis, phosphatic stones and extensive tubulointerstitial fibrosis; (3) cystinuria, an isolated defect in tubular reabsorption of cystine and dibasic aminoacids, which results only in the formation of stones but requires a cumbersome treatment. Analysis of stones appears of crucial value for the early diagnosis of these diseases, as in several of them the morphology and composition of stones is specific. In other cases, especially if nephrocalcinosis, phosphatic stones or proteinuria are present, the evaluation of blood and urine chemistry, especially with regard to calcium, phosphate and magnesium, is the key of diagnosis. Search for mutations is now increasingly performed in as much as genetic counselling is important for the detection of heterozygotes in autosomic recessive diseases and of carrier women in X-linked diseases. In conclusion, better awareness to the rare monogenic forms of nephrolithiasis and/or nephrocalcinosis should allow early diagnosis and treatment which are needed to prevent or substantially delay progression of end-stage renal disease. Analysis of every first stone both in children and in adults should never be neglected, in order to early detect unusual forms of nephrolithiasis requiring laboratory evaluation and deep etiologic treatment.

Calcimimetics as an adjuvant treatment for familial hypophosphatemic rickets

BACKGROUND AND OBJECTIVES

The treatment for X-linked hypophosphatemia (XLH) with phosphate and calcitriol can be complicated by secondary hyperparathyroidism and nephrocalcinosis. Furthermore, vitamin D and phosphate stimulate FGF23 production, the pathogenic factor causing XLH. We investigated in XLH patients: 1) whether treatment with the calcimimetic agent, cinacalcet, will block the rise in parathyroid hormone (PTH) caused by phosphate administration; and 2) whether treatment with oral phosphate and calcitriol increases FGF23 levels.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Eight subjects with XLH were given a single oral dose of phosphate, followed the next day by combined treatment with phosphate and cinacalcet. Serum measurements of ionized calcium (Ca), phosphate, creatinine, intact PTH, 1,25(OH)(2)D, FGF23, and tubular threshold for phosphate/glomerular filtration rate (TP/GFR) were assessed in response to short-term treatment with phosphate and cinacalcet and compared with long-term administration of phosphate and calcitriol.

RESULTS

Oral phosphate load increased serum phosphate, decreased ionized calcium, and increased PTH. Twenty-four hours later, FGF23 significantly increased and 1,25(OH)(2)D decreased. The concomitant administration of phosphate and cinacalcet resulted in further decrease in serum Ca(2+) but suppression of PTH and greater increase in serum phosphate and TP/GFR. Chronic treatment with phosphate and calcitriol resulted in a smaller increment in serum phosphate and high serum FGF23.

CONCLUSIONS

Traditional therapy of XLH with phosphate and calcitriol elevates FGF23 and has the potential to stimulate PTH. Short-term treatment with cinacalcet suppresses PTH, leading to increase in TP/GFR and serum phosphate. Thus, long-term clinical studies are needed to investigate whether cinacalcet may be a useful adjuvant in the treatment of XLH, allowing the use of lower doses of phosphate and calcitriol.

Hypophosphatemia: clinical consequences and management

Current evidence regarding the clinical consequences of hypophosphatemia is not straightforward. Given the potentially different implications of hypophosphatemia among various patient groups, this commentary touches on patients with low serum phosphate after acute hospitalization, those with chronic ambulatory hypophosphatemia, and those with hypophosphatemia in the setting of advanced renal disease. Finally, this commentary examines the evidence regarding how best to replete phosphorous in the hypophosphatemic patient.

How fibroblast growth factor 23 works

There is a discontinuum of hereditary and acquired disorders of phosphate homeostasis that are caused by either high or low circulating levels of the novel phosphaturic hormone fibroblastic growth factor 23 (FGF23). Disorders that are caused by high circulating levels of FGF23 are characterized by hypophosphatemia, decreased production of 1,25-dihydroxyvitamin D, and rickets/osteomalacia. On the other end of the spectrum are disorders that are caused by low circulating levels of FGF23, which are characterized by hyperphosphatemia, elevated production of 1,25-dihydroxyvitamin D, soft tissue calcifications, and hyperostosis. Knowledge of the genetic basis of these hereditary disorders of phosphate homeostasis and studies of their mouse homologues have uncovered a bone-kidney axis and new systems biology that govern bone mineralization, vitamin D metabolism, parathyroid gland function, and renal phosphate handling. Further understanding of this primary phosphate homeostatic pathway has the potential to have a significant impact on the diagnosis and treatment of disorders of bone and mineral metabolism.

Severe kyphoscoliosis associated with osteomalacia

BACKGROUND CONTEXT

Kyphoscoliosis is one of the most frequent complications of osteomalacia, which only rarely results in severe deformity requiring surgery. To the best of our knowledge, there has been only one previous report of a spinal deformity as a complication of osteomalacia that was sufficiently severe so as to require surgical treatment.

PURPOSE

To report here the case of a 27-year-old woman who experienced back pain of gradual onset accompanied by progressive scoliosis resulting in severe dyspnea.

STUDY DESIGN

A case report.

METHODS

She was diagnosed with hypophosphatemic osteomalacia and secondary hyperparathyroidism. She underwent posterior surgical correction and fusion from Th4-L1 using the ISOLA spinal system.

RESULTS

At the last follow-up (3 year and 9 months postoperatively), her body balance was good and the dyspnea had disappeared. Plain radiographs demonstrated no loss of correction and also showed no evidence of instrumentation failure.

CONCLUSIONS

We present a unique instance of a young woman with severe kyphoscoliosis who underwent posterior surgical correction/fusion with spinal instrumentation.

Role of prostaglandins in the pathogenesis of X-linked hypophosphatemia

X-linked hypophosphatemia is an X-linked dominant disorder resulting from a mutation in the PHEX gene. PHEX stands for phosphate-regulating gene with endopeptidase activity, which is located on the X chromosome. Patients with X-linked hypophosphatemia have hypophosphatemia due to renal phosphate wasting and low or inappropriately normal levels of 1,25-dihydroxyvitamin D. The renal phosphate wasting is not intrinsic to the kidney but likely due to an increase in serum levels of fibroblast growth factor-23 (FGF-23), and perhaps other phosphate-wasting peptides previously known as phosphatonins. Patients with X-linked hypophosphatemia have short stature, rickets, bone pain and dental abscesses. Current therapy is oral phosphate and vitamin D which effectively treats the rickets and bone pain but does not adequately improve short stature. In this review, we describe recent observations using Hyp mice; mice with the same mutation as patients with X-linked hypophosphatemia. We have recently found that Hyp mice have abnormal renal prostaglandin production, which may be an important factor in the pathogenesis of this disorder. Administration of FGF-23 in vivo results in phosphaturia and an increase in prostaglandin excretion, and FGF-23 increases proximal tubule prostaglandin production in vitro. In Hyp mice, indomethacin improves the phosphate transport defect in vitro and in vivo. Whether indomethacin has the same effect in patients with X-linked hypophosphatemia is unknown.

[Hyperparathyroidism associated with hypophosphatemic osteomalacia: case report and review of the literature]

Adult-onset hypophosphatemic osteomalacia is a rare disease characterized by hypophosphatemia, increased levels of alkaline phosphatase and decreased bone mass. Oral supplementation with phosphate and vitamin D is the main treatment and, in cases of oncogenic osteomalacia, tumor resection is mandatory. We report the case of a patient with hypophosphatemic osteomalacia of an unknown cause. Despite extensive search, no tumor was found. The patient was treated with phosphate for a long period and developed tertiary hyperparathyroidism. Serum PTH levels did not return to normal after surgical excision of three parathyroids and the patient refused to continue clinical investigation and treatment. After ten years absent from the hospital, during which medications were used irregularly, she was admitted with multiple fractures and respiratory insufficiency caused by severe thoracic deformities, and died. The authors discuss the relationship between osteomalacia and hyperparathyroidism and the aggressive course of the disease.

Hypophosphatemic rickets: results of a long-term follow-up

This study reports the benefits and side effects of conventional treatment, phosphate and calcitriol supplementation in patients with heritable hypophosphatemic rickets and a long-term follow-up, median of 60.9 months. The group is composed of 17 patients (ten girls). Sixteen patients presented with bone pain and/or deformities, and in one patient the diagnosis was radiological. All the patients had increased alkaline phosphatase, hypophosphatemia, decreased fractional phosphate tubular reabsorption (TRP) and maximum tubular phosphate reabsorption/glomerular filtration rate ratio (TPO4/GFR). Ten of 17 patients had metabolic acidosis, which was corrected only with the conventional treatment. Potassium citrate was prescribed to the patients who developed hypercalciuria. Excluding one patient with pulmonary dysfunction, the remaining 16 patients were divided into two groups according to the age at treatment onset (T0): group I (GI) > or =4 years (n =9) and GII <4 years (n =7). GI and GII had similar follow-up periods and treatment protocols. Seven out of nine GI patients underwent orthopedic surgery, in contrast to none of GII. Anthropometric data results showed that within each group there is no difference in weight and stature z -score at T0 and at the end of the observation (Tf), but, when both groups are compared, GII shows higher z-score for stature at T0 (p <0.05) and at Tf (p <0.05). Nephrocalcinosis developed in three cases and correlated with hypercalciuria (p <0.001) and dose of calcitriol (p =0.03). In conclusion, higher stature z-score is associated with early treatment. A careful protocol is recommended to detect such complications as nephrocalcinosis. We suggest potassium citrate for patients with hypercalciuria to avoid calcium precipitation.

Hypophosphatémies génétiquement déterminées chez l’adulte

Hereditary hypophosphatemic rickets groups together X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets (ADHR) and hereditary hypophosphatemic rickets with hypercalciuria (HHRH, autosomal recessive). Clinical and biological characteristics and treatment depend on specific etiology. Mutations causing hereditary hypophosphatemic rickets involve PHEX located on Xp11.22 for XLH and FGF-23 located on 12p13 for ADHR. The gene involved in HHRH remains unknown: candidates may encode proteins that modulate phosphate transporter expression or activity. Others forms of rickets must be ruled out: acquired hypophosphatemia due to oncogenic osteomalacia, X-linked recessive hypophosphatemic rickets or Dent's disease, and hereditary 1, 25-dihydroxyvitamin D-resistant rickets with a defect either in the 1-alpha-hydroxylase gene (pseudo-vitamin D deficiency rickets, PDDR) or in the vitamin D receptor (hereditary vitamin D-resistant rickets, HVDRR).

Resolution of medullary nephrocalcinosis in children with metabolic bone disorders

Ultrasonographic resolution of nephrocalcinosis (NC) has been reported in children with furosemide-induced NC, but not in other entities. We report the cases of four children with metabolic bone disease, two with hypophosphatasia and two with X-linked hypophosphatemic rickets, in whom we observed resolution of renal calcifications. At the time of ultrasonographic resolution of NC, 3 of the patients were on anticalciuric diuretics, and all 4 had normal urinalysis, serum creatinine and electrolyte profiles, as well as estimated creatinine clearance. In 3 of the children, evidence of mild tubular dysfunction was found. It thus seems that in some children with bone and mineral disorders who develop NC, ultrasonographic resolution of the renal calcifications can be seen; however, mild tubular dysfunction may remain and require follow-up. Further studies are suggested to explore the possible role of anticalciuric diuretics in promoting the resolution of NC.

A clinical and molecular genetic study of hypophosphatemic rickets in children

X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets, hereditary hypophosphatemic rickets with hypercalciuria, and tumor-induced osteomalacia share clinical and biochemical features, and are collectively referred to as hypophosphatemic rickets (HR). Recently, the molecular bases of HR were elucidated. A review of medical records and mutational analyses of the PHEX and FGF23 genes were performed on 17 unrelated Korean children with HR. The male-to-female ratio was 3:14, and 5 patients were familial. Initial laboratory tests revealed typical features of HR. Seven different PHEX mutations were detected in 8 patients: 2 missense mutations, 2 nonsense mutations, and 3 short deletions. No functional FGF23 mutation was detected in any patient. Patients with the PHEX mutation tended to have more severe skeletal disease than those without. Of the patients with this mutation, no genotype-phenotype correlation and no gene dosage effect were noted. Treatment with vitamin D and phosphate resulted in only a partial growth improvement in most cases, and was frequently complicated by hypercalciuria, hypercalcemia, nephrocalcinosis, or hyperparathyroidism. Renal glycosuria was detected in six cases and was associated with more severe skeletal disease. We conclude that current HR treatment is not fully safe or effective, and that close monitoring of treatment effectiveness and for complications should be performed during long-term treatment. No genotype-phenotype correlation in XLH was detected in this study, but a large-scaled study on this topic is warranted. The large proportion of patients with a normal genetic study suggests the possibility of other causative gene(s).

Cyclic bisphosphonate therapy in osteogenesis imperfecta type V

The clinical and radiographic features and management of a young person with recently delineated Osteogenesis Imperfecta Type V is described. A female aged 9 years presented with a history of multiple fractures since 3 years of age and bilateral dislocation of the elbows from infancy. She was commenced on a low dose frequent regimen of cyclic intravenous pamidronate, which resulted in progressive improvement in bone density, reduced fracture frequency and remission of symptoms of osteoporosis.

Renal phosphate wasting disorders: clinical features and pathogenesis

Rickets and osteomalacia are associated with hypophosphatemia in several disease states, including X-linked hypophosphatemic rickets, autosomal-dominant hypophosphatemic rickets, and tumor-induced osteomalacia. Recent advances in the understanding of these diseases include discovery of mutations in the genes encoding human phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and fibroblast growth factor 23 (FGF-23) and the finding of overproduction of FGF-23 and other proteins including matrix extracellular phosphoglycoprotein (MEPE) and frizzled-related protein 4 (FRP-4) in tumor-induced osteomalacia. Research is ongoing to better define how these proteins relate to each other and to the sodium-phosphate cotransporter in both normal and abnormal phosphate metabolism. New and improved therapies for disorders of phosphate metabolism, osteomalacia, and rickets will develop as our knowledge of phosphate metabolism grows.

Correction of proximal tubule phosphate transport defect in Hyp mice in vivo and in vitro with indomethacin

X-linked hypophosphatemia is the most prevalent inherited form of rickets. In this disorder, rickets results from hyperphosphaturia and inappropriately normal levels of 1,25(OH)2-vitamin D. Current therapy with oral phosphate and vitamin D improves the rickets, but has significant morbidity and does not significantly affect the short stature and hypophosphatemia. In the present study, we demonstrate that Hyp mice, which have a mutation homologous to that in patients with X-linked hypophosphatemia, have a 2-fold greater urinary prostaglandin E2 (PGE2) excretion than C57/B6 mice. To determine whether PGs were involved in the pathogenesis of this disorder, Hyp and C57/B6 mice received i.p. injections with vehicle or indomethacin (1 mg/kg of body weight twice daily for 4 days) and were studied approximately 12 h after the last dose of indomethacin. In the Hyp mice, indomethacin treatment decreased the fractional excretion of phosphate from 13.0 +/- 3.2% to 2.2 +/- 1.1% (P < 0.05), and increased serum phosphate from 2.9 +/- 0.2 mg/dl to 4.1 +/- 0.2 mg/dl (P < 0.05). There was no effect of indomethacin in C57/B6 mice. Indomethacin did not affect serum creatinine or inulin clearance, demonstrating that the normalization of urinary phosphate excretion was not caused by changes in glomerular filtration rate. Indomethacin treatment increased renal brush border membrane vesicle NaPi-2 protein abundance in Hyp mice to levels comparable to that of C57/B6 mice, but had no effect in C57/B6 mice. In vitro isolated perfused proximal tubule studies demonstrate directly that 10-6 M bath indomethacin normalized the phosphate transport defect in Hyp mice but had no effect on C57/B6 mice. In conclusion, there is dysregulation of renal PG metabolism in Hyp mice, and indomethacin treatment normalizes the urinary excretion of phosphate by a direct tubular effect.

Early treatment improves growth and biochemical and radiographic outcome in X-linked hypophosphatemic rickets

X-Linked hypophosphatemic rickets (XLH) is characterized by hypophosphatemia, rickets, and impaired growth. Despite oral phosphate and 1,25-dihydroxyvitamin D(3) treatment, many patients have suboptimal growth and bone healing. The aim of this study was to assess whether age at treatment onset impacts the outcome. Growth data, biochemistry, and radiographs of 19 well-controlled patients with XLH were analyzed retrospectively. Patients were divided into two groups based on the age at treatment onset (group 1, <1.0 yr; group 2, >or=1.0 yr). The median height z-score was higher in group 1 (n = 8) than in group 2 (n = 11) at treatment onset [-0.4 SD score (SDS) vs. -1.7 SDS; P = 0.001], at the end of the first treatment year (-0.7 SDS vs. -1.8 SDS; P = 0.009), throughout childhood (P > 0.05) and until predicted adult height (-0.2 SDS vs. -1.2 SDS; P = 0.06). The degree of hypophosphatemia was similar in both groups, but serum alkaline phosphatase remained higher in group 2 throughout childhood. Radiographic signs of rickets were more marked in group 2, but even patients with early treatment developed significant skeletal changes of rickets. These data suggest that treatment commenced in early infancy results in improved outcome in patients with XLH, but does not completely normalize skeletal development.

Prolonged high-dose phosphate treatment: a risk factor for tertiary hyperparathyroidism in X-linked hypophosphatemic rickets

OBJECTIVE

X-linked hypophosphatemic rickets is characterized by renal phosphate wasting, hypophosphatemia and defective bone mineralization. Treatment with oral phosphate (Pi) and calcitriol improves skeletal changes but associates with secondary hyperparathyroidism and nephrocalcinosis. Tertiary hyperparathyroidism is a rare complication of the treatment. The aim of the present study was to identify treatment-related factors that might be associated with the transition of secondary hyperparathyroidism to tertiary hyperparathyroidism in patients with X-linked hypophosphatemic rickets.

DESIGN

Thirteen patients with X-linked hypophosphatemic rickets and secondary or tertiary hyperparathyroidism were included in the study. Their hospital records were reviewed and compared for onset, duration and dosage of treatment, and for age of diagnosis and degree of secondary hyperparathyroidism.

RESULTS

Two patients developed tertiary hyperparathyroidism and 11 patients secondary hyperparathyroidism during the treatment. Patients with tertiary hyperparathyroidism had, on average, earlier onset and longer duration of treatment, higher dose of Pi and longer duration of treatment with very high Pi doses (> 100 mg/kg/day) compared to the 11 patients with secondary hyperparathyroidism. However, variation of all parameters was great with considerable overlap. Very high S-PTH levels > or = 42 pmol/l were observed in those who later developed tertiary hyperparathyroidism.

CONCLUSIONS

Prolonged very high dose oral Pi treatment is a major risk factor for the development of tertiary hyperparathyroidism in X-linked hypophosphatemic rickets.

Hypertension in hypophosphatemic rickets--role of secondary hyperparathyroidism

Hypertension has been anecdotally reported in children with familial hypophosphatemic rickets (XLH). To better identify and characterize the clinical and laboratory features of hypertensive XLH children, we reviewed the medical records of 41 XLH children, all treated with phosphate and vitamin D analogues. Eight children, who were originally normotensive, developed hypertension during the 2nd decade of life. At diagnosis of hypertension all had persistent secondary/tertiary hyperparathyroidism (HPTD), defined as high serum parathyroid hormone (PTH) for 12 months or longer. Seven had nephrocalcinosis (NC). Analysis of data showed that of 11 children with HPTD, 8 developed hypertension compared with 0 among 30 without HPTD (P<0.001). Of 40 children studied, 18 had NC that was significantly associated with both HPTD (P<0.01) and hypertension (P<0.025). At diagnosis of hypertension, serum calcium was elevated in 2. Plasma renin activity was high in 3 of 4 patients in whom it was measured. Doppler ultrasonography or renal scan was normal in the 5 children studied. Early echocardiography showed left ventricular hypertrophy in only 2 of 5 children studied. In 3 patients who underwent parathyroidectomy, hypertension persisted and 1 progressed to renal failure. Serum creatinine remained normal in all others. Successful treatment of hypertension consisted of beta-adrenergic blockers, angiotensin converting enzyme inhibitors, and Ca channel blockers as monotherapy or in combination. We conclude that hypertension in treated XLH children is closely associated with HPTD. Emphasis should therefore be placed on prevention of the development of HPTD as a complication of XLH treatment, and close monitoring for hypertension in those who do develop HPTD.

Tertiary hyperparathyroidism after high-dose phosphate therapy in adult-onset hypophosphatemic osteomalacia

OBJECTIVE

To describe a case of adult-onset hypophosphatemic osteomalacia treated with orally administered phosphate and complicated by tertiary hyperparathyroidism.

METHODS

We present pertinent clinical, radiologic, and laboratory details of the study patient for a period of more than 20 years and discuss the few reported cases of tertiary hyperparathyroidism attributable to prolonged phosphate therapy.

RESULTS

A 49-year-old Jordanian man, who had been diagnosed at age 26 years as having sporadic adult-onset hypophosphatemic vitamin D-resistant osteomalacia, presented with severe right hip pain, severe osteopenia with lytic bone lesions, and hypercalcemia after prolonged oral treatment with phosphate and vitamin D. These clinical, radiologic, and biochemical findings, in conjunction with a very high serum parathyroid hormone level, indicated the diagnosis of tertiary hyperparathyroidism, which was substantiated histopathologically.

CONCLUSION

Physicians should be aware of the potential for development of tertiary hyperparathyroidism in patients receiving prolonged oral phosphate therapy.

Ectopic cardiac calcification associated with hyperparathyroidism in a boy with hypophosphatemic rickets

An adolescent with hypophosphatemic rickets developed cardiac calcifications in the absence of hypercalcemia or elevation of the phosphocalcic product (the product of the total serum calcium and phosphorus concentrations). Cardiac calcifications led to aortic and mitral valve dysfunction, myocardial calcification, and arrhythmia. Hyperparathyroidism probably played a significant role in the development of this complication, which emphasizes the necessity for intermittent assessment of parathyroid status in individuals receiving medical therapy for hypophosphatemic rickets.

Thiazide diuretics arrest the progression of nephrocalcinosis in children with X-linked hypophosphatemia

OBJECTIVE

X-linked hypophosphatemia (XLH) is characterized clinically by rickets, hypophosphatemia, and hyperphosphaturia. Conventional treatment of XLH with oral phosphate and vitamin D is associated with increased urinary calcium excretion and nephrocalcinosis. Thiazide diuretics decrease urinary calcium excretion. The objective of this study was to determine the effect of thiazide diuretics on the clinical and radiologic course of nephrocalcinosis in children with XLH.

METHODS

The effect of hydrochlorothiazide (HCTZ) on clinical and radiologic progression of nephrocalcinosis was evaluated in 11 children with XLH. All patients had been treated previously with vitamin D and oral phosphate and had radiologic evidence of nephrocalcinosis. The average age of the patients at the start of HCTZ was 6.6 +/- 1.0 years. The effect of oral HCTZ at 0.8 +/- 0.1 mg/kg body weight per day given for 3.3 +/- 0.6 years on the progression of nephrocalcinosis and urinary calcium excretion was evaluated.

RESULTS

There was no change in serum phosphorous, calcium, potassium, and chloride after HCTZ therapy. HCTZ therapy increased serum bicarbonate and decreased urinary calcium excretion. The grade of nephrocalcinosis increased from 0.4 +/- 0.2 to 1.5 +/- 0.3 in the 2.3 +/- 0.3 years before initiation of HCTZ therapy, whereas the degree of nephrocalcinosis was stable after 3.3 +/- 0.6 years of HCTZ therapy (1.5 +/- 0.3 vs 3.0 +/- 0.3).

CONCLUSION

HCTZ decreased urinary calcium excretion but did not result in the resolution of nephrocalcinosis. However, when compared with the control period, HCTZ prevented the progression of nephrocalcinosis in children with XLH.

Effect of growth hormone treatment on final height, phosphate metabolism, and bone mineral density in children with X-linked hypophosphatemic rickets

OBJECTIVE

To evaluate the effect of growth hormone treatment on final height, phosphate metabolism, bone markers, and bone mineral density in children with X-linked hypophosphatemic rickets.

STUDY DESIGN

Six patients (aged 7.8 +/- 1.8 years; height z score, -3.4 +/- 0.5) received conventional treatment (1,25-dihydroxyvitamin D(3) plus phosphate salts) combined with growth hormone (0.6-0.9 IU/kg per week, subcutaneously) (group A); 6 patients (aged 7.9 +/- 2.5 years; height z score, -2.1 +/- 0.6, P <.01 with respect to group A) received only conventional treatment (group B).

RESULTS

Final height z score significantly improved in group A (-2.4 +/- 0.5, P <.03 with respect to the value at entry), whereas it did not change in group B (-2.8 +/- 0.5, P = NS). At final height, degree of body disproportion was similar between the groups (group A, 1.3 +/- 0.2; group B, 1.2 +/- 0.1; P = NS). Phosphate retention, bone markers, and radial bone mineral density increased only in group A. No adverse effects were observed.

CONCLUSIONS

In poorly growing patients with X-linked hypophosphatemic rickets, growth hormone therapy combined with conventional treatment improves final height, phosphate retention, and radial bone mineral density, but it does not influence degree of body disproportion.

Etiology of nephrocalcinosis in preterm neonates: association of nutritional intake and urinary parameters

BACKGROUND

Nephrocalcinosis (NC) in preterm neonates has been described frequently, and small-scale studies suggest an unfavorable effect on renal function. The etiologic factors have not yet been fully clarified. We performed a prospective observational study to identify factors that influence the development of NC.

METHODS

The study population consisted of 215 preterm neonates with a gestational age <32 weeks. Clinical characteristics and intake in the first four weeks of calcium, phosphorus, vitamin D, protein, and ascorbic acid were noted. Serum calcium, phosphate, vitamin D, magnesium, uric acid, creatinine, urea and urinary calcium, phosphate, oxalate, citrate, magnesium, uric acid, and creatinine were assessed at four weeks of age and at term. Renal ultrasonography (US) was performed at four weeks and at term. At term was defined as a postconceptional age of 38 to 42 weeks.

RESULTS

NC was diagnosed by means of US in 33% at four weeks and in 41% at term. Patients with NC at four weeks had a significantly higher mean intake of calcium (P < 0.05), phosphorus (P < 0.05), and ascorbic acid (P < 0.01) than patients without NC. They had a higher mean serum calcium (2.55 vs. 2.46 mmol/L, P < 0.01) and a higher mean urinary calcium/creatinine ratio (2.6 vs. 2.1 mmol/mmol, P < 0.05). Patients with NC at term had a lower birth weight (1142 vs. 1260 g, P < 0.05) and a lower gestational age (28.8 vs. 29.4 weeks, P < 0.05), were treated significantly longer with furosemide, dexamethasone, theophylline, and thiazides, developed chronic lung disease more frequently (40 vs. 16%, P < 0.001), and had a higher mean urinary calcium/creatinine ratio (2.7 vs. 2.3 mmol/mmol, P < 0.05) and a lower mean urinary citrate/calcium ratio (1.1 vs. 1.7 mmol/mmol, P = 0.005).

CONCLUSIONS

NC develops as a result of an imbalance between stone-inhibiting and stone-promoting factors. A high intake of calcium, phosphorus, and ascorbic acid, a low urinary citrate/calcium ratio, a high urinary calcium/creatinine ratio, immaturity, and medication to prevent or treat chronic lung disease with hypercalciuric side effects appear to contribute to the high incidence of NC in preterm neonates.

The effects of bone marrow transplantation on X-linked hypophosphatemic mice

The genes responsible for X-linked hypophosphatemic (XLH) vitamin D-resistant rickets and the murine homolog, hypophosphatemic mice (Hyp), were identified as PHEX and Phex (phosphate-regulating gene with homology to endopeptidases on the X chromosome), respectively. However, the mechanism by which inactivating mutations of PHEX cause XLH remains unknown. We investigated the mechanisms by syngeneic bone marrow transplantation (BMT) from wild mice to Hyp mice. The expression of the Phex gene was detected in mouse BM cells. BMT introduced a chimerism in recipient Hyp mice and a significant increase in the serum phosphorus level. The renal sodium phosphate cotransporter gene expression was significantly increased. The effect of BMT on the serum phosphorus level depended on engraftment efficiencies, which represent the dosage of normal gene. Similarly, the serum alkaline phosphatase (ALP) activity was decreased and bone mineral density was increased. Furthermore, the renal expression of 25-hydroxyvitamin D3 24-hydroxylase, which is a key enzyme in the catabolic pathway and is increased in XLH/Hyp, was improved. From these results, we conclude that transplantation of normal BM cells improved abnormal bone mineral metabolism and deranged vitamin D metabolism in Hyp by replacing defective gene product(s) with normal gene product(s). This result may provide strong evidence for clinical application of BMT in metabolic bone disorders.

A trial of growth hormone therapy in well-controlled hypophosphataemic rickets

OBJECTIVE

Conventional therapy of hypophosphataemic rickets (HR) with oral phosphate and calcitriol does not always result in normal linear growth. Recombinant human growth hormone (rhGH) offers theoretical advantages as an adjunctive therapy. We aimed to determine the effects of adjunctive rhGH therapy in children with well-controlled HR.

PATIENTS

In this report, 5 prepubertal children (aged 3.5-10.9 years) with well-controlled HR on conventional therapy were given adjunctive standard dose rhGH therapy for one year.

DESIGN AND MEASUREMENTS

Height, growth velocity, metabolic markers of calcium and phosphate metabolism, body composition, bone mineral density, wrist and knee X-rays, and renal sonography were assessed at regular intervals. Height and growth velocities were also calculated 12 months after ceasing rhGH therapy.

RESULTS

After 12 months therapy with rhGH, no significant biochemical or radiological benefits were observed. A significant increase in height SD score was observed (P = 0.023), but this was not associated with any increase in the growth velocity SD score and appears to have been due to catch-up growth caused by conventional therapy alone. When rhGH therapy was ceased, no significant decreases in mean height SD or growth velocity SD scores were observed.

CONCLUSIONS

In well-controlled hypophosphataemic rickets patients receiving conventional therapy, adjunctive therapy with standard dose rhGH offers no benefits in linear growth or rachitic disease markers.

X-linked hypophosphatemia: normal renal function despite medullary nephrocalcinosis 25 years after transient vitamin D2-induced renal azotemia

Nephrocalcinosis (NC) detected by ultrasound is a recognized abnormality for some patients with X-linked hypophosphatemia (XLH) who received vitamin D2 and inorganic phosphate therapy, but is commonly observed in XLH patients treated with 1,25-dihydroxyvitamin D3 and inorganic phosphate supplementation. Nevertheless, long-term follow-up of kidney function in XLH patients with NC detected ultrasonographically has not been reported. We investigated two women with XLH, ages 31 (patient 1) and 39 (patient 2) years, each of whom had suffered at least one documented episode of vitamin D2-induced hypercalcemia and renal azotemia during childhood. Patient 2 had also been treated with inorganic phosphate. No medications for XLH had been taken during adulthood. Renal ultrasonography at our institution demonstrated marked bilateral medullary NC in both women. No other explanation was found for their NC that apparently occurred several decades earlier from medical therapy for XLH. Detailed studies (including creatinine clearance, beta2-microglobulin excretion, and fasting urinary osmolality and acidification) revealed no impairment of kidney function in either patient. Our findings indicate that subradiographic medullary NC acquired during medical therapy for XLH may persist for decades, but with no adverse renal sequelae. Definitive (long-term) assessment of kidney function in the XLH population with NC, however, will be necessary to fully understand the risk of current medical treatment for this most common heritable form of rickets.

The effect of recombinant human growth hormone in children with X-linked hypophosphatemia

BACKGROUND

X-linked hypophosphatemia (XLH) is characterized clinically by rickets and growth retardation. Conventional treatment of XLH with oral phosphate and vitamin D fails to normalize linear growth. Objective. To determine the benefit and the potential side effects of recombinant human growth hormone (rhGH) therapy in patients with XLH.

DESIGN AND METHODS

A randomized, double-blind, crossover study was performed throughout a 24-month period in five children with XLH, each patient serving as his own control. The effect of 12 months of rhGH therapy on height, mineral metabolism, glucose and lipid metabolism, hemoglobin, thyroid and parathyroid function, serum 1,25-(OH)2 vitamin D, osteocalcin, growth hormone, urinary calcium, phosphate, nephrocalcinosis, renal function, and bone density was compared with the effects of 12 months of placebo administration on the same parameters.

RESULTS

The average age (mean +/- SEM) of the patients at the start of the study was 5.6 +/- 1.4 years. Growth hormone therapy improved the height standard deviation score (z-score) from a baseline of -2.66 +/- 0.21 to -2.02 +/- 0.25 and to -1.46 +/- 0.28, after 3 and 12 months, respectively. At the start of the control period the height z-score was -2.27 +/- 0.30 compared with -2.22 +/- 0.16 after 12 months of placebo administration. The growth velocity standard deviation score was -1. 90 +/- 0.40 during the 12 months of placebo administration and +4.04 +/- 1.50 during the 12 months of rhGH therapy. An increase in serum phosphate from 0.88 +/- 0.07 mmol/L to 1.17 +/- 0.14 mmol/L and tubular maximum for phosphate reabsorption (TmP/GFR) from 2.12 +/- 0. 15 to 3.41 +/- 0.25 mg/dL, was observed after 3 months of rhGH therapy. However, both serum phosphate and TmP/GFR were unchanged from baseline after 6, 9, and 12 months of rhGH therapy. Neither serum phosphate nor TmP/GFR changed from baseline during the placebo administration. Insulin-like growth factor 1 (IGF-1) increased from 114 +/- 25 to 354 +/- 51 ng/mL after 12 months of rhGH therapy. Despite the increase in IGF-1 after rhGH therapy, the value did not exceed normal serum concentration. IGF-1 did not change from baseline after 12 months of placebo administration. Neither therapy with rhGH nor with placebo had an effect on glucose and lipid metabolism, hemoglobin, thyroid and parathyroid function, serum 1, 25-(OH)2 vitamin D, alkaline phosphatase, osteocalcin, urinary calcium excretion, the grade of nephrocalcinosis, glomerular filtration rate, or urinary albumin excretion. Twelve months of rhGH therapy increased bone mass and width but not density. Twelve months of placebo administration had no effect on bone mass, width, or density.

CONCLUSION

Patients with XLH have an improvement in linear growth and a transient increase in serum phosphate attributable to a transient decrease in urinary phosphate excretion when treated with rhGH.

Medical management and complications of X-linked hypophosphatemic vitamin D resistant rickets

To improve the growth failure, bowed legs, and biochemical and radiological abnormalities in patients with X-linked hypophosphatemic vitamin D resistant rickets (XLH), combined therapy of phosphate and calcitriol is the best therapeutic approach at present. However, the complications involving combined therapy, such as hypercalcemia, nephrocalcinosis and hyperparathyroidism, are not fully solved. To achieve better control, new therapeutic approaches have been reported recently, for example, growth hormone (GH) or new vitamin D analogs. GH improved linear growth, decreased phosphate reabsorption and increased 1-alpha-hydroxylase activity. Furthermore, 24R,25-dihydroxyvitamin D3 (24,25) improved the bone lesions in hypophosphatemic (Hyp) mice, and also in XLH, without the adverse effects such as hypercalcemia or hypercalciuria compared with 1,25-dihydroxyvitamin D3. These new approaches should be considered for the treatment of patients with XLH.

Osteomalacia

Osteomalacia is a generalized bone disorder characterized by impairment of mineralization, leading to accumulation of unmineralized matrix or osteoid in the skeleton. The classical clinical features of osteomalacia include musculoskeletal pain, skeletal deformity, muscle weakness and symptomatic hypocalcaemia. In childhood the features of osteomalacia are accompanied by rickets, with widening of the epiphyses and impaired skeletal growth. The major cause of osteomalacia is vitamin D deficiency, which is most often due to reduced cutaneous production of vitamin D in housebound elderly people, immigrants to Northern countries and women who adopt strict dress codes which prohibit exposure of uncovered skin. Vitamin D deficiency osteomalacia may also occur with malabsorption, liver disease and anticonvulsant therapy. Less commonly, osteomalacia may result from abnormal vitamin D metabolism, resistance to the action of vitamin D, hypophosphataemia or toxic effects on osteoblast function.

New perspectives on the biology and treatment of X-linked hypophosphatemic rickets

This article updates the practicing pediatrician's knowledge of the hypophophatemic disorders that may occur in children. The classic X-linked disorder is emphasized. Details of clinical manifestations, the wide spectrum of disease severity, and complications of the disorder in adults are reviewed. Recent research, new genetic findings, and speculations regarding pathophysiology are discussed. A strategy for approaching medical treatment of X-linked hypophosphatemic rickets is provided, together with complications of treatment and treatment after cessation of growth.

Craniosynostosis in X-linked hypophosphataemic rickets

A report of three cases of craniosynostosis in X-linked hypophosphataemic rickets (XLH) is presented. The literature is reviewed, suggesting that craniosynostosis is relatively common in XLH and that boys may be more at risk than girls. It is recommended that radiological screening be offered to all patients with XLH.

Effects of serum phosphate level on formation of incisor dentine in hypophosphatemic mice

The effects of serum phosphate level on the formation of incisor dentine were investigated in hypophosphatemic (Hyp) mice fed a diet high in calcium and phosphorus (high Ca/P diet). Feeding a high Ca/P diet for more than 10 days resulted in an increase in the serum phosphate level in Hyp mice to one similar to that of normal mice. Lower incisors were cut transversely at the centre of the length of the incisor, a point that had taken approximately 40 days to be reached from the start of dentine formation in Hyp mice. Transverse views of the incisors showed a triangle-like outline in Hyp mice fed a control diet, while the outline became rounded in Hyp mice fed the high Ca/P diet for more than 40 days. In Hyp mice fed the high Ca/P diet for 40 days interglobular dentine was still observed and fluorescent lines produced by tetracycline showed a diffuse and wavy pattern in incisor dentine; however, interglobular dentine became indistinct and fluorescent lines showed a relatively smooth pattern in the incisor dentine of Hyp mice fed the diet for more than 60 days.

Comparison of 22-oxacalcitriol and 1,25(OH)2D3 on bone metabolism in young X-linked hypophosphatemic male mice

Using a mouse model (Hyp) of human hypophosphatemic vitamin D-resistant rickets [X-linked hypophosphatemia (XLH)], we compared the effects of 22-oxa-1,25-dihydroxyvitamin D3 (OCT) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on restoring defects in mineral and skeletal metabolism. Hyp/Y mice received OCT or 1,25(OH)2D3 at doses of 0.05-0.25 micron.kg-1.day-1 for 4 wk. OCT normalized serum calcium levels, whereas 1,25(OH)2D3 produced hypercalcemia in Hyp/Y. OCT and 1,25(OH)2D3 also normalized serum phosphate levels and increased urinary calcium levels. Additionally, OCT and 1,25(OH)2D3 reduced elevated urinary pyridinoline levels and suppressed urinary adenosine 3',5'-cyclic monophosphate levels to normal. Bone ash content was low in Hyp/Y, and OCT was more effective than 1,25(OH)2D3 in reversing this defect. Histomorphometric analysis of bone turnover, mineralization rate, and osteoid content demonstrated comparable responses with OCT and 1,25(OH)2D3, although the highest dose of 1,25(OH)2D3 resulted in increased osteoid content and delayed mineralization. OCT appears to be more effective and definitely less toxic than 1,25(OH)2D3 in reversing skeletal lesions in Hyp/Y mice and may prove to be the drug of choice in the treatment of childhood XLH.

Recurring oral giant cell lesion in a child with X-linked hypophosphatemic rickets: clinical manifestation of occult parathyroidism?

A 9-year-old boy with X-linked hypophosphatemic rickets had a recurring oral giant cell lesion. These lesions are relatively uncommon in children and represent a potentially aggressive disorder that is microscopically indistinguishable from the brown tumors of hyperparathyroidism. Subclinical hyperparathyroidism is not uncommon in X-linked hypophosphatemic rickets and may account for the giant cell lesion in this patient.

Medullary nephrocalcinosis in nephropathic cystinosis

Children with nephropathic cystinosis excrete large amounts of calcium and phosphate due to renal tubular Fanconi syndrome, and also receive substantial supplements of phosphate and alkalinizing agents. Since these constitute risk factors for nephrocalcinosis, we evaluated 41 children age 2 months to 15 years with nephropathic cystinosis and good renal function by performing retroperitoneal ultrasound examinations in a blinded fashion. We also retrospectively analyzed parameters of calcium and phosphate metabolism representing 216 person-years of data on these children. Fifteen children had no evidence of medullary nephrocalcinosis, while 18 had mild nephrocalcinosis, and 8 severe nephrocalcinosis; 5 had renal stones. Mean urine calcium and phosphate concentrations increased from 1.47 mM and 5.30 mM, respectively, in children without nephrocalcinosis to 1.60 mM and 5.69 mM in children with mild nephrocalcinosis to 1.66 mM and 6.19 mM in children with severe nephrocalcinosis. Mean urine pH ranged from 7.5 to 8.1. The mean (+/- SD) age of the 26 patients with nephrocalcinosis was 9.4 +/- 3.8 years compared with 5.1 +/- 3.8 years for those without nephrocalcinosis (P < 0.005). Serum calcium, phosphate, vitamin D, and parathyroid hormone did not correlate with frequency or degree of nephrocalcinosis. We conclude that nephrocalcinosis frequently accompanies nephropathic cystinosis, can be detected by ultrasound examination, and might be managed by reducing oral replacement of phosphate, calcium, vitamin D, and citrate. Consideration should be given to truncating phosphate replacement once bone growth ceases.

Nephrocalcinosis in X-linked hypophosphatemia: effect of treatment versus disease

While the literature has suggested that vitamin D and phosphate therapy benefits children, and possibly adults, with X-linked hypophosphatemia (XLH), there have been increasing reports of nephrocalcinosis by renal ultrasound examination in treated patients. Although it has been assumed that nephrocalcinosis is the result of treatment, there has been no systematic comparison of treated and untreated XLH patients with long-term follow-up. Therefore, we studied 10 adults and 4 children by renal ultrasound examination with no history of medical therapy and 10 adults and 8 children with a history of medical therapy. None of the untreated patients had nephrocalcinosis; 5 treated adults and 5 treated children had nephrocalcinosis. In 3 of 4 treated children, serial renal ultrasounds did not show progression of the nephrocalcinosis. One patient progressed from baseline to year 1 only. Comparisons of means between treated patients without and with nephrocalcinosis showed statistically significant differences for urine calcium/creatinine ratios and urine phosphorus/creatinine ratios, differences not seen between untreated patients and treated patients without nephrocalcinosis. Phosphate dose, but not vitamin D dose, was statistically significantly different between the two treated groups. Our studies point to a convincing role for the association between nephrocalcinosis, as diagnosed by renal ultrasound examination, and medical therapy.

Autonomous hyperparathyroidism in X-linked hypophosphataemia

Four patients with familial hypophosphataemic rickets developed significant hypercalcaemia which persisted after discontinuation of vitamin D therapy. They had increased PTH levels and were operated for hyperparathyroidism at the ages of 18, 20, 24 and 45 years, respectively. Three of the patients had previously received phosphate treatment and one patient developed hyperparathyroidism 7 years after treatment with calcitriol. Histological evaluation revealed different degrees of parathyroid hyperplasia in all patients, with persistently increased PTH and/or calcium levels after surgery. The possibility of autonomous hyperparathyroidism should be evaluated in the follow-up of patients with X-linked hypophosphataemic rickets.

Hypercalciuria and ultrasound abnormalities in children with cystinosis

We noted microscopic haematuria in children with cystinosis. To investigate this we studied urinary calcium excretion and undertook renal ultrasound scans. Most patients had elevated urinary calcium excretion and all had abnormal appearances on ultrasound scan, ranging from increased cortical echogenicity only to those with increased cortical and medullary echogenicity. The ultrasound scan appearance was graded and correlated with laboratory parameters. It remains unclear as to the aetiology of the ultrasound findings and whether they are a consequence of treatment or a hitherto unrecognised feature of the disease.

Oral calcium treatment in vitamin D-dependent rickets type II

Vitamin D-dependent rickets type II is a rare hereditary disease that results from target organ resistance to the action of 1,25-dihydroxyvitamin D3. There is a great heterogeneity in the clinical presentation of this condition. The affected patients usually present early in childhood with clinical and biochemical evidence of rickets. Physiological replacement dosage of 1,25-dihydroxyvitamin D3 has no therapeutic effect. Responses to pharmacological doses of vitamin D metabolites or long-term calcium infusion have been variable. A case is reported here of an 8 year old girl, of consanguineous parents with vitamin D-dependent rickets, type II, in whom treatment with high dose oral calcium resulted in marked biochemical and radiological improvement. It is concluded that high dose oral calcium treatment is an effective treatment option for patients with vitamin D-dependent rickets type II.

Growth hormone secretion in poorly growing children with renal hypophosphataemic rickets

We evaluated growth hormone (GH) secretion and baseline serum free insulin-like growth factor-I (IGF-I) levels in 12 poorly growing patients (5 males and 7 females; age 1.6-12.5 years, median 6.4) with renal hypophosphataemic rickets treated with 1,25-dihydroxy-vitamin D3 plus inorganic oral phosphate salts. Eleven healthy normally growing children (6 males and 5 females; age 3.1-10.8 years, median 6.6) were studied as control group. All patients had a normal GH response (GH peak > or = 10 micrograms/l) to at least one provocative pharmacological stimulus (levodopa or insulin tolerance test), as well as all the controls. Mean growth hormone concentrations (MGHC), mean pulse amplitude, number of GH peaks above 5 micrograms/l, and IGF-I values overlapped between patients and controls, even though four patients had MGHC below the lower limit of MGHC of controls. In these patients, however, height-SDS, serum calcium, phosphate, alkaline phosphatase, intact parathyroid hormone, 1,25-dihydroxyvitamin D concentrations and maximum tubular phosphate reabsorption/glomerular filtration rate ratio did not differ in respect to the patients who showed MGHC in the range of controls (n = 6). MGHC IGF-I and biochemical parameters of phospho-calcium metabolism did not differ when the patients were subdivided in two groups on the basis of the median (-2.4) of height-SDS. No relationship was found between MGHC or IGF-I and height-SDS or growth velocity-SDS. Height-SDS and years of treatment or age at which therapy was started were not related.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutics of X-linked hypophosphatemic rickets

X-linked hypophosphatemia, the most common form of familial rickets, is conventionally treated with 1,25-dihydroxyvitamin D3 (5-50 ng/kg per day) plus phosphate supplementation (70-100 mg/kg per day). However, nephrocalcinosis is noted in many children treated with this therapy. Whether to treat or not and whether such treatment should be continued into adulthood or in pregnancy are unsettled questions. This article reviews these controversies and provides current recommendations.

Growth in children with X-linked hypophosphataemic rickets

Currently, X-linked hypophosphataemic rickets (XLHR) is most commonly treated with a combination of phosphate and vitamin D, but there is conflicting evidence about the effects of this treatment on linear growth. In all, 25 patients with XLHR (current age range, 4.1-22.1 years; median, 8.2 years) were studied to determine whether there was any improvement in height SDS during treatment. The duration of therapy was 2.9-15.0 years (median, 5.7 years). Measurements before the age of 2 years or after the onset of puberty were excluded to remove the effects of measurement difficulties in small infants and of variation in pubertal timing. The growth of these patients was compared with a similar group of untreated historical controls. Patients treated with calcitriol and phosphate for at least 2 years before the onset of puberty (n = 22) had a significantly better mean height SDS than the historical controls (-1.23 compared with -2.05 for the historical controls; p = 0.02). Among patients treated with calcitriol and phosphate for at least 2 years (n = 21), the change in height SDS had a positive correlation with the duration of therapy (r = 0.51; p = 0.02). The growth of children with XLHR treated with combination therapy was thus significantly better than that of historical controls.