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PubMed1989

X-linked hypophosphatemia.

X-linked hypophosphatemia is a common cause of metabolic rickets in children in this country. The gene defect is localized to the Xp22 region in man. Research into this disorder has been enhanced by the discovery of a mutant gene named Hyp on the X chromosome of mice that produces a syndrome similar to the human disease. These mutant genes in humans and mice alike result in low renal tubular reabsorption of phosphate, rickets, and osteomalacia. The renal synthesis of 1,25-dihydroxyvitamin D is unresponsive to low phosphate stimuli in both. A second mutant gene on the X chromosome of mice, Gy, also causes low renal tubular reabsorption of phosphate. The underlying defects in both the human disease and the mouse models are unknown. The availability of these murine models should advance our understanding of this clinical disorder and provide an environment for the testing of novel therapies.

Animals↗
PubMed1989

Hypercalciuric hypophosphatemic rickets, mineral balance, bone histomorphometry, and therapeutic implications of hypercalciuria.

A 14-year-old Turkish boy had severe rickets that had been clinically evident since he was 2 years of age. When he was 5 years of age, he had normal serum calcium and phosphorus levels and increased alkaline phosphatase activity. Treatment with modest dosages of vitamin D (5000 U/d for 3 weeks) resulted in hypercalcemia. At 10 years of age, high-dose vitamin D (40,000 U/d) plus phosphorus (1.1 g/d) therapy for 20 days resulted in symptomatic nephrolithiasis. When, 14 years of age, he had normocalcemia, hypophosphatemia, increased alkaline phosphatase activity, and normal circulating parathyroid hormone concentration. Levels of 25-hydroxyvitamin D were normal but those of 1,25-dihydroxyvitamin D were markedly increased. Rickets and osteopenia were evident on radiographs, and osteomalacia was present on trabecular bone obtained at biopsy. Balance study results showed increased intestinal absorption of calcium and phosphorus, hypercalciuria, and increased urinary phosphorus excretion. This patient manifests an unusual form of hypophosphatemic rickets in which hypercalciuria is a cardinal feature. In contrast with most varieties of hypophosphatemia, this disorder is characterized by appropriately increased production of 1,25-dihydroxyvitamin D in response to hypophosphatemia. It is recommended that urinary calcium excretion be assessed in all patients with hypophosphatemic rickets so that appropriate therapy will be instituted.

Adolescent↗
PubMed1989

X-linked hypophosphatemia: a clinical, biochemical, and histopathologic assessment of morbidity in adults.

Research and management of XLH have concentrated on the disease in childhood, and the natural history and morbidity of XLH in adult life are thus poorly understood. We have studied 22 adults (6 men) with XLH to clarify these aspects of this most common inherited form of rickets and osteomalacia. Most study participants had presented with rickets in early childhood and had undergone tibial osteotomies on at least 1 occasion. Seventeen individuals had genu varum, 1 had genu valgum, and 4 had straight legs, attributable to successful osteotomies in 2. Five subjects reported increasing lower limb deformity in the late teens or subsequently. Eight subjects complained of bone pain, 6 of whom had radiologic evidence of pseudofractures; pseudofractures were found in 4 additional asymptomatic individuals. None of 16 subjects who underwent transiliac bone biopsy had normal double tetracycline labeling; accordingly, all were considered to have osteomalacia. Bone pain was associated with a relative osteoid volume in excess of 25%. Relative osteoid volume was inversely related to serum 1,25(OH)2D concentration (r = -0.74, p less than 0.02), but unrelated to serum concentrations of calcium and phosphate or their product. Eighteen participants complained of joint pain, predominantly in the knees and ankles. The severity of joint pain correlated with the degree of lower limb deformity (p = 0.011) which, in turn, was related to fasting serum phosphate concentration (r = -0.56, p less than 0.025) and TmP/GFR (r = -0.70, p less than 0.005). Enthesopathy affected 33% of those younger than 30 years, and all those above this age. Nineteen individuals had experienced significant dental problems, most commonly abscess formation. Eight had required complete dental clearance. Twelve women from the group had a total of 22 live births. Fifteen of these were by cesarean section, although radiologic evidence of pelvic narrowing was not found in any subject. Serum ALP was elevated in all but 3 of the 18 untreated subjects. Levels correlated with those of other indices of bone turnover (BGP r = 0.82, p less than 0.005; urine total HP r = 0.60, p less than 0.025; urine free HPr = 0.78, p less than 0.005), but were not related to the degree of osteomalacia found on bone biopsy. Serum levels of iPTH, 25(OH)D, 1,25(OH)2D, and thyroid hormones were generally normal in the untreated patients. We conclude that adults with untreated XLH have osteomalacia that is frequently symptomatic. Even greater morbidity is caused by degenerative joint disease arising from lower limb deformities.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1988

[Morphological changes in the jejunal mucosa in vitamin D-resistant rickets].

Sixteen children with vitamin-D deficiency underwent jejunoscopy with spot jejunal biopsy. Morphologic evaluation of the biopsy specimens provided evidence for glycocalyx destruction and malabsorption syndrome. Hyperactivity of hydrolytic enzymes may be concerned with the adjustment to a disturbance of the calcium/phosphorus metabolism.

Child↗
PubMed1988

Principles and results of corrective lower limb osteotomies for patients with vitamin D-resistant hypophosphatemic rickets.

Forty-four lower limb osteotomies were performed in ten patients with vitamin D-resistant hypophosphatemic rickets. The average follow-up period was 51 months. Osteotomies were combined with shortening and compression plating. This allowed corrections of angular deformities in the sagittal plane as large as 70 degrees and in the coronal plane as large as 78 degrees. There was one complication, a compartment syndrome that resolved completely following prompt fasciotomy. Recurrence of deformity occurred in 27% of the cases. While osteotomies were safe and provided dramatic improvement to limb deformity, postoperative control of vitamin D metabolism was the one constant factor for maintenance of correction.

Adolescent↗
PubMedDate not supplied

[Effect of strontium on the anti-rickets activity of vitamin D3 and its hydroxy analogs].

Antirickets activity of vitamin D3 and of its derivatives 1 alpha- and 25-hydroxy vitamin D3 1.25- and 24,25-dihydroxy vitamin D3 and 1,24,25-trihydroxy vitamin D3 was studied in chicken maintained on a diet containing various amount (0.01-2.40 mg) of strontium. Vitamin D3 as well as its 24-hydroxy and 24,25-dihydroxy derivatives lost their antirickets activity in presence of high strontium concentrations. Under the same conditions I alpha-hydroxy, 1,25-dihydroxy and 1,24,25-trihydroxy vitamins D3 retained the ability both to induce calcium-binding protein synthesis in intestinal epithelium and to stimulate bone tissue mineralization, although to a lesser degree as compared with controls, kept on strontium-free diet. These results suggest that presence of I alpha-OH-group in the steroid molecule is necessary for expression of maximal biological activity under conditions of elevated strontium content in diet while the activity of hydroxylase is inhibited in kidney. At the same time, the vitamin D3 derivatives containing the OH-group are responsible for impairments caused by increased accumulation of strontium.

24,25-Dihydroxyvitamin D 3↗
PubMed1986

Acquired hypophosphataemic vitamin D resistant rickets in black children.

The case histories of five black children aged between 4 1/2 and 9 years, with acquired hypophosphataemic vitamin D resistant rickets are presented. Muscle weakness was a striking feature clinically, while radiographically all had marked osteopenia in association with classical florid rickets. Biochemically, they were normocalcaemic and hypophosphataemic, with normal parathyroid hormone concentrations. In three of the children 1,25-dihydroxyvitamin D concentrations were low. One child responded to no specific therapy, while three required continuous 1 alpha-hydroxyvitamin D and oral phosphate supplementation, and the fifth 1 alpha-hydroxyvitamin D therapy alone before the clinical, biochemical and radiographic picture responded. The features in three of the children resemble oncogenous rickets, but the features of the other two do not fit any known aetiology. Although the group as a whole may be heterogeneous, until the pathogenetic mechanisms are determined, the authors believe they should be grouped together as acquired hypophosphataemic vitamin D resistant rickets.

Calcitriol↗