Acceleration of growth with combined vitamin D-phosphate therapy of hypophosphatemic resistant rickets

Growth in PHEX-associated X-linked hypophosphatemic rickets: the importance of early treatment

Inactivating mutations in phosphate-regulating endopeptidase (PHEX) cause X-linked hypophosphatemic rickets (XLHR) characterized by phosphaturia, hypophosphatemia, bony deformities, and growth retardation. We assessed the efficacy of combined calcitriol and orally administered phosphate (Pi) therapy on longitudinal growth in relation to age at treatment onset in a retrospective, single-center review of children with XLHR and documented PHEX mutations. Growth was compared in those who started treatment before (G1; N = 10; six boys) and after (G2; N = 13; five boys) 1 year old. Median height standard deviation score (HSDS) at treatment onset was normal in G1: 0.1 [interquartile range (IR) -1.3 to 0.4) and significantly (p = 0.004) lower in G2 (IR -2.1 (-2.8 to -1.4). Treatment duration was similar [G1 8.5 (4.0-15.2) vs G2 11.9 (6.2-14.3) years; p = 0.56], as were prescribed phosphate and calcitriol doses. Recent HSDS was significantly (p = 0.009) better in G1 [-0.7 (-1.5 to 0.3)] vs G2 [-2.0 (-2.3 to -1.0)]. No effects of gender or genotype on growth could be identified. Children with PHEX-associated XLHR benefit from early treatment and can achieve normal growth. Minimal catchup growth was seen in those who started treatment later. Our findings emphasize the importance of early diagnosis to allow treatment before growth has been compromised.

[Hypophosphatemic diabetes and knee pain: does treatment with total knee arthroplasty promise success?]

Hypophosphatemic diabetes, a rare metabolic disease, presents in children, young adults as well as in elderly patients. In this report we describe the case of a 43-year-old woman with known hypophosphatemic diabetes who complained of severe knee pain after several osteotomies of the lower extremities. The patient was treated with bilateral total knee arthroplasty. The immediate post-operative outcome was good but showed deterioration at 12-month follow-up with decreased range of motion due to ligament stiffness. Knee arthroplasty in patients with hypophosphatemic diabetes remains a challenge for the orthopaedic surgeon. Arthroplasty can be recommended in severe knee pain; however, pre-operative interventions should be considered to prevent post-operative complications.

Anthropometric characteristics of X-linked hypophosphatemia

An anthropometric study was undertaken to assess head proportions of patients with X-linked hypophosphatemia (XLH). Fourteen morphometric parameters of the head were measured and 10 cephalic indices calculated in 82 affected persons (57 females and 25 males) from 55 unrelated families with XLH, and compared with the results obtained in the group of their healthy relatives (37 females and 33 males), as well as with general population control values. Normalized values (SD, z-score) were analyzed statistically. The group of healthy relatives, both males and females, differed significantly from Polish population control values in most of the normalized variables measured, making population control values useless as a control group for the analyzed XLH group. Intrafamilial values of cephalic parameters in healthy relatives of the XLH patients were finally applied for statistical analysis. Generally patients with XLH showed highly statistically significant increase in head length (males 0.95 +/- 1.07 vs. -0.37 +/- 1.02, females 0.57 +/- 1.59 vs. -0.06 +/- 1.15), significant decrease in occipital breadth (males -0.56 +/- 1.27 vs. 0.70 +/- 1.28, females -0.59 +/- 1.7 vs. 0.13 +/- 1.1) and several milder anomalies of craniofacial proportions. Mean cephalic index was significantly lower in XLH patients when compared with the healthy relatives (males -0.909 vs. 0.278 P < 0.0001, females -0.705 vs. 0.381 P = 0.007). The cephalic changes were found both in XLH children and XLH adults and were more pronounced in affected males than in females. There were no differences between offspring born by hypophosphatemic and normophosphatemic mothers.

The pattern of growth and growth retardation of patients with hypophosphataemic vitamin D-resistant rickets: a longitudinal study

Growth in height of 16 patients (5 boys and 11 girls) with hypophosphataemic rickets (HR) was studied in a longitudinal survey. The data shortly before and during puberty were analysed on the basis of Preece Baines curves, fitted to the original data; for the analysis at the age of 5 years, the original data were used. It appeared that the overall shape of the individual and average growth pattern could be adequately described by the Preece Baines method. The results further showed that from the age of 5 years onwards, average height was approximately two standard deviations below the normal mean for Dutch children. The patients showed a normal pubertal growth spurt which was, in general, insufficient to restore the growth retardation already established before adolescence. The four children who did show catch-up growth between the age of 5 years and adulthood had minimal rachitic lesions. The greater impact of the disease on growth in early childhood than on adolescent growth could be explained by the fact that HR mainly affects the growth of the legs, the major contributor to body size in early childhood. Finally, it was found that the difference between bone age, as determined by the Tanner Whitehouse (TW2)-method, and chronological age was not significant and the adult height in all patients except two could be adequately predicted from bone age and height.

X-linked hypophosphatemic rickets: a study (with literature review) of linear growth response to calcitriol and phosphate therapy

Not all children with X-linked hypophosphatemia (XLH) have demonstrated improved linear growth with calcitriol [1,25-(OH)2D3] and inorganic phosphate (Pi) therapy. To assess which factors are associated with a favorable growth response during this treatment, we retrospectively compared demographics and biochemical parameters of bone metabolism to the linear growth patterns of 20 children with XLH who were prepubertal and had not required osteotomy. A total of 15 patients had family histories consistent with XLH; 5 appeared to be sporadic cases. During 3 years of therapy, the growth velocities of 12 patients had been at or above the mean for age (good growers) and those of 8 patients had been below the mean (poor growers). Data from the two groups were contrasted. We found no difference between the good growers and poor growers before or after the 3 year period of therapy in mean age, dietary calcium, calcitriol dose or compliance, or Pi dose or compliance. Both groups increased their mean fasting serum Pi levels with treatment. The TmP/GFR (mean +/- SEM) of the good growers improved with therapy (1.9 +/- 0.2 to 2.6 +/- 0.2 mg/dl, p = 0.01), and their posttreatment value was higher compared to that of the poor growers (2.6 +/- 0.1 versus 2.2 +/- 0.1 mg/dl, p = 0.02). However, their enhanced TmP/GFR was not associated with a reduction in serum iPTH levels (before, 693 +/- 50; after, 688 +/- 76 pg/ml; p = 0.9). The Z test for binomial proportions showed that the group that grew well contained a disproportionate number of girls (10 of 12, p = 0.04). Our findings suggest that calcitriol may exert a direct effect on the renal tubule to improve Pi reclamation in XLH. The observation that heterozygous girls appear to respond better than hemizygous boys to calcitriol and Pi therapy provides evidence for a gene dosage effect in the expression of this X-linked dominant disorder.

X linked hypophosphataemia: treatment, height gain, and nephrocalcinosis

The clinical data of 18 patients with X linked hypophosphataemia were analysed retrospectively. The height data were expressed as SD scores. There was no difference in the final height of patients treated with vitamin D (or 1,25-dihydroxyvitamin D) and phosphate for at least two years (n = 12) and that of 16 hypophosphataemic family members who had never been treated. The mean final SD score (-2.07) of treated patients, however, was significantly higher than the value before treatment (-2.79), which indicated an average absolute height gain of 4-4.5 cm compared with the expected height values. Six of the treated patients developed ultrasonographically detectable nephrocalcinosis with normal renal function. The daily phosphate intake and excretion of patients with nephrocalcinosis was significantly higher than that of patients with normal renal morphology. There was no difference in the doses of vitamin D between the two groups. The average urinary calcium:creatinine ratio of the two groups was similar to and below the hypercalciuric 0.6 mmol:mmol limit. The group with nephrocalcinosis, however, had a higher incidence of hypercalciuric episodes than the group without nephrocalcinosis (12 in 130 observations compared with six in 334 observations, respectively). The benefits and risks of treatment of patients with X linked hypophosphataemia must be further evaluated. The high dose of phosphate seems to be an important factor in the development of nephrocalcinosis in this group of patients.

Evidence suggesting hyperoxaluria as a cause of nephrocalcinosis in phosphate-treated hypophosphataemic rickets

Urinary excretion of oxalate and phosphate was measured in twelve vitamin-D-treated, phosphate-supplemented patients with X-linked hypophosphataemia (XLH; four children, eight adolescents and adults) to investigate possible causative factors of nephrocalcinosis other than calcium. Oxalate excretion correlated highly with urinary phosphate excretion and with intake of phosphate supplements corrected for body surface area. Young children received the highest relative doses of phosphate (range 2.27-10.8 g/1.73 m2 daily) and their urinary oxalate excretion was very high (0.94-3.38 mmol/1.73 m2 daily). The urinary oxalate excretion of untreated adults with XLH was within normal limits. Six patients had evidence of nephrocalcinosis on ultrasound. The high urinary oxalate excretion in phosphate-supplemented XLH may be seen as a special type of enteric hyperoxaluria, in which the conditions of calcium-oxalate crystal precipitation could be reached even at normal levels of urinary calcium excretion. Urinary excretion of both calcium and oxalate should therefore be monitored during treatment in young XLH patients.

The relation between attained adult height and the metaphyseal lesions in hypophosphataemic vitamin-D resistant rickets

In 13 young adult patients (5 men and 8 women) adult height was correlated with the average rachitic activity on radiographs of the wrist, taken at intervals during childhood. To this end the rachitic activity was classified into 4 different, clearly distinguishable stages according to its severity. The coefficient of correlation between adult height (expressed as standard deviation score) and the average rachitic activity or score was -0.796 (p less than 0.01), indicating that adult height varied inversely with the severity of the disease. The regression equation between adult height (y) and the rachitic score (x) was: y = -1.53x + 0.90; the SEy was 0.76. Although the coefficient of correlation was highly significant, this value for SEy indicated that much of the observed variation was due to other factors, apart from the rachitic process.

Bone response to phosphate salts, ergocalciferol, and calcitriol in hypophosphatemic vitamin D-resistant rickets

We treated 11 children with vitamin D-resistant rickets with a phosphate mixture either alone (1.2 to 3.6 g per day) or combined with ergocalciferol (vitamin D2, to 50 x 103 IU per day) or with calcitriol (1,25-dihydroxyvitamin D3, 0.25 to 1 microgram per day). Serum calcitriol concentrations were normal in all patients. Calcitriol therapy circulating levels of the hormone to values above normal and increased intestinal phosphate absorption. In some patients this regimen decreased the need for phosphate supplements. None of the treatment regimens corrected the renal phosphate leak. Radiologic studies and bone histomorphometric analyses showed that phosphate (alone or with ergocalciferol) induced the mineralization of the growth plate but not of the endosteal bone surface. Combined calcitriol and phosphate therapy for a total of 2850 patient-days greatly improved the mineralization of trabecular bone. Short-term episodes of hypercalcemia were easily controlled by changes in calcitriol dosage. The data indicate that the combined calcitriol and phosphate regimen is useful in the treatment of vitamin D-resistent rickets.

Growth and glucocorticoids in children with kidney disease

Glucorticoid therapy inhibits statural growth. Alternate-day therapy causes less growth suppression than does daily therapy, and, in experimental animals and children with asthma, it has been associated with normal growth. Although catch-up growth may occur after cessation of steroid therapy, this is not always the case, especially when therapy has been prolonged. In children treated with steroids for glomerulonephritis or nephrotic syndrome and especially in children after renal transplantation, factors other than steroid therapy may contribute to growth retardation. Steroids may suppress growth by direct action on cell metabolism, by inhibition of growth hormone or somatomedin and/or by effects on calcium and phosphorus metabolism. Present knowledge of mechanisms of action and dose-response relationships is complete, and it is difficult to prescribe therapy which will achieve a predictable therapeutic effect without inhibiting growth.

Recent advances in calcium metabolism. II. Disorders of calcium homeostasis

Abnormalities of calcium and mineral metabolism are described in relation to the differential diagnosis, clinical characteristics, diagnostic procedures, and treatment of infants and children with hypocalcemia, hypercalcemia, rickets, chronic renal insufficiency, and other disorders of calcium metabolism. Understanding of the basic pathogenesis of each abnormality of calcium homeostasis is essential for the rational management of affected patients.