The management of siblings with familial hypophosphatemic rickets

Two siblings (boy and girl) born to a mother with familial hypophosphatemic rickets had abnormal values of serum phosphorus and serum alkaline phosphatase at the age of six weeks. At this age therapy with 1 alpha-hydroxycholecalciferol (1 alpha OHD3) and phosphate was started resulting in both siblings having normal growth of body length and radiological healing of the bone lesions but persistently low values of fasting serum phosphorus during the time of observation up to 60 and 26 months of age, respectively. Phosphate and 1 alpha OHD3 have a positive influence on serum phosphorus through their effect on the intestine. Neither of the patients developed hypercalcaemia during treatment. It seems, therefore, that the early administration of 1 alpha OHD3 with phosphate in infants with familial hypophosphatemic rickets prevents dwarfism and has a positive effect on intestinal absorption of phosphorus but not on fasting hypophosphatemia.

Serum osteocalcin in the treatment of inherited rickets with 1,25-dihydroxyvitamin D3

Osteocalcin is a vitamin K-dependent protein, synthesized in bone, which can be detected in serum. We have measured circulating osteocalcin levels in 10 patients with x-linked hypophosphatemia (XLH) and in 6 patients with autosomal recessive vitamin D dependence (ARVDD) who started 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] therapy. Patients with XLH were studied before and after 7-12 months of therapy that included 1,25-(OH)2D3 (10-72 ng/kg x day) and oral phosphate. Serum osteocalcin rose from 28 +/- 12 to 52 +/- 12 ng/ml (mean +/- SE; P less than 0.01) in concert with improvements in biochemical status and bone mineralization. Vitamin D therapy was withdrawn for 2 weeks from patients with ARVDD. The vitamin D-deplete status was evidenced by low 1,25-(OH)2D3 levels (12 +/- 2 pg/ml; n = 6). After 1 week of therapy with 1,25-(OH)2D3, serum calcium rose from 9.03 +/- 0.21 to 9.67 +/- 0.25 mg/dl (P less than 0.002), while serum phosphorus and alkaline phosphatase remained unchanged. Serum osteocalcin rose from 35 +/- 7 to 83 +/- 32 ng/ml (P less than 0.05). At 3 weeks, serum calcium remained elevated (9.63 +/- 0.18 ng/dl) over control levels (P less than 0.01); phosphorus and alkaline phosphatase were still unchanged. Serum osteocalcin rose to 114 +/- 42 ng/ml, significantly greater than values at 1 week (P less than 0.05). Thus, serum osteocalcin increases after 1,25-(OH)2D3 therapy in both ARVDD and XLH.

New developments in the vitamin D endocrine system

Vitamin D must be altered first by 25-hydroxylation in the liver and subsequently by 1-hydroxylation in the kidney in order to stimulate intestinal calcium transport, bone calcium mobilization, intestinal phosphate transport, and renal tubular reabsorption of calcium. Other pathways of vitamin D metabolism are described, and evidence is presented which indicates that only 25- and 1-hydroxylation pathways are activation mechanisms. The 1 alpha-hydroxylation step is regulated by the need for calcium and the need for phosphorus. The vitamin D hormone, 1,25-dihydroxyvitamin D3, appears to act in target tissues by virtue of interacting with a receptor appearing in the nucleus and eliciting transcription of specific genetic information that codes for calcium and phosphorus transport proteins. Diseases of calcium and phosphorus metabolism in which there is a disturbance of the vitamin D endocrine system and the use of the vitamin D metabolites are discussed.

Early biochemical findings in familial hypophosphataemic, hyperphosphaturic rickets and response to treatment

Regular biochemical measurements were made in 4 babies, each of whom had one parent with familial hypophosphataemic, hyperphosphaturic rickets. Hypophosphataemia developed by 2 months and levels of alkaline phosphatase had increased by 3 months in all four. Decreased tubular reabsorption of phosphate and x-ray changes of rickets did not develop until 6 months in 3 of the babies. In the fourth these abnormalities developed at 9 days and 3 months. The babies were treated with oral phosphate and small doses of 1-alpha-hydroxy-cholecalciferol. The rickets healed readily in 3 babies and their linear growth kis within the normal range. Healing took much longer in the remaining child and his linear growth is below the 3rd centile. Hypercalcaemia has not been a problem of treatment.

[Hereditary pseudovitamin-D-deficiency rickets with alopecia as a consequence of extreme resistance of target organs to 1.25-(OH)2-cholecalciferol. Therapeutic progress in another disorder of vitamin-D-metabolism (author's transl)]

We report about a pair of Turkish siblings suffering from alopecia and severe rickets. In the elder sister we could show the causal role of extreme resistance of target organs to 1.25-(OH)2-cholecalciferol. The birth of a brother who developed the same symptoms together with two other similar cases in siblings recently published by other authors, made it possible to recognize the disorder as a typical syndrome-like entity, based on a hereditary defect. By successful administration of excessive (and so-far not previously published) doses of Vitamin-D3 a way for therapeutic progress in this new type of vitamin-D-dependent rickets is shown.

[Familial form of idiopathic hypercalciuria with nanism, bone and renal involvement in children]

A brother and a sister are reported, demonstrating the severe form of childhood idiopathic hypercalciuria associated with dwarfism, renal defects and bone lesions (rickets and osteoporosis). The family are Israeli Beduins from a small village with a highly inbred population. The parents who are first cousins, and the remaining 6 siblings are not affected. This suggests an autosomal recessive form of transmission for the trait.

[X-linked familial hypophosphatemic rickets report of six cases (author's transl)]

X-linked familial hypophosphatemic rickets (X.L.F.H.R.) is one of the D resistant rickets. The inheritance pattern is related to the X chromosome. Most constant feature is hypophosphatemia. Pathogenesis is still a subject of controversy. There are three main theories: a) An abnormal vitamin D metabolism. b) Secondary hyperparathyroidism developping as a result of the diminished calcium absorption by gut. c) A primary deffect of phosphate transport al various levels. Authors study and comment six cases of X.L.F.H.R., three of which belong to the same family. Clinical, radiological and higtological findings correspond to those of severe rickets. It is a chronic disease which affects children during growth period, giving rise to deforming bones invalidism. Treatment consists on continuous administration of oral phosphate and vitamin D.

Serum 1,25-dihydroxyvitamin D levels in normal subjects and in patients with hereditary rickets or bone disease

The serum concentration of 1,25-dihydroxylvitamin D (1,25-[OH]2D) in normal children and in children with inherited diseases of bone was compared by use of a competitive binding assay. Observed values were: in 12 normal children and adolescents, 37.1 +/- 1.9 pg per milliliter (mean +/- S.D.); in 14 patients with X-linked hypophosphatemic rickets treated with vitamin D2 and phosphate supplements, 15.6 +/- 7.8 (P less than 0.01 versus control); in six patients with autosomal recessive vitamin D dependency treated with vitamin D2, 9.5 +/- 2.9 (P less than 0.01 versus control); and in four untreated patients with autosomal dominant hypophosphatemic (non-rachitic) bone disease, 30.2 +/- 6.3 (not significantly different from the controls). The difference in bone disease between X-linked hypophosphatemia (severe) and hypophosphatemic bone disease (mild) at comparable low serum levels of phosphate implies that 1,25-(OH)2D and phosphate may have independent roles in the pathogenesis of defective bone mineralization.

Hereditary hypophosphataemic rickets with autosomal recessive inheritance and severe osteosclerosis. A report of two cases

We have observed congenital hypophosphataemic rickets in two sons of a marriage between first cousins, their mother being clinically and biochemically normal. Both patients are now approaching middle age. In addition to severe childhood rickets and lifelong hypophosphataemia, their disease is characterised by gross osteosclerosis with extraskeletal ossification, clinically persistent osteomalacia in one and spinal cord compression in the other. The genetics of this disease can be satisfactorily explained only on the basis of autosomal recessive inheritance, a mode which has only once before been reported in the literature. The severity of certain features, which would be expected in a homozygous state, may help our understanding of the more usual X-linked form.

Susceptibility of a dwarf strain of chickens to rickets

A sex-linked dwarf strain of chickens fed a practical chick starter had a high incidence of rickets while other strains, including the Cornell K strain reared under the same conditions, had no evidence of this disease. In studies of the calcium, phosphorus and vitamin D requirements of the dwarf and K strains, no strain differences in requirement for phosphorus or vitamin D for maximal bone mineralization were apparent. The vitamin D requirement for growth was less for dwarfs than for the K strain; the reverse was observed for phosphorus. A marginal level of calcium (0.6%) did not depress growth or bone ash in either strain. Dwarfs had significantly lower bone ash than chicks of the K strain when dietary levels of calcium, available phosphorus and vitamin D were adequate (1.0%, 0.73% and 400 I.U./kg., respectively). When the diet contained a low level of one nutrient (0.6% calcium, 0.33% of phosphorus or 100 I.U./kg. vitamin D), neither strain was affected. Low levels of two nutrients significantly decreased bone ash in dwarfs but not in the K strain. Low levels of all three nutrients depressed bone ash in both strains, but most markedly in the dwarfs. These studies indicate that chicks of the Cornell dwarf strain have a low bone mineral content and are unusually susceptible to rickets.

Vitamin-D deficiency rickets in Jamaican children

Vitamin-D deficiency is not as rare in Jamaica as previously believed. 9 children with vitamin-D deficiency rickets have been seen at the University Hospital of the West Indies during the past 5 years. All were over 3 years of age at time of presentation. Both dietary deficiency of vitamin D and lack of exposure to sunlight seem to be important causes. Children living in rural Jamaica seem to be more susceptible to the disease than those living in a city, due perhaps to more prolonged breast feeding and lack of fortified milk feeds on weaning.

Genetic aspects of nutritional rickets

Amino acid excretion was investigated in 21 rachitic infants and in 22 of their parents. There was (a) increased alpha-amino acid excretion in one-third of the infants a long time after the rickets had healed, (b) an abnormally high excretion of alpha-amino nitrogen and of phosphorus in many of the parents (c) an abnormal pattern of amino acid excretion in all 9 infants tested, and (d) a good correlation between the excretion of individual amino acids by an infant and by its parents. Our findings suggest that in at least some cases of nutritional rickets there is a genetic element which may manifest itself only under adverse environmental conditions.

Parathyroid hormone status and renal responsiveness in familial hypophosphatemic rickets

Basal serum and urinary biochemical parameters and their response to PTH or calcium infusion were examined in 14 untreated patients with familial hypophosphatemic rickets (FHR) from 5 kindreds and 9 normal control subjects after a period of dietary equilibration. FHR subjects exhibited significantly elevated basal serum iPTH levels (FHR: 11.4 +/- 0.8, controls: 5.1 +/- 0.5 ng/ml, P less than 0.001) and urinary cAMP excretion (FHR: 7.83 +/- 0.81, controls: 3.78 +/- 0.46 nmol/mg creatinine P less than 0.001). In response to PTH infusion (6 units/kg over 4 hours) FHR subjects exhibited a mean 34% decrease in TRP and a 22-fold increase in cAMP excretion, both comparable to the control response. Calcium infusion (10 mg/kg over 1 h) rapidly suppressed serum iPTH and urinary cAMP values in FHR subjects. However, TRP remained inappropriately low for the level of serum phosphate. Basal and post-calcium infusion serum iPTH levels correlated positively with urinary cAMP in FHR subjects and controls. Pre- and post-calcium infusion iPTH levels correlated with serum calcium in FHR subjects. Mean Salivary phosphate concentration was significantly reduced in FHR subjects (FHR: 12.68 +/- 0.87, controls: 22.47 +/- 2.16 mg/100 ml, P less than 0.001). However, calculated salivary phosphate clearance rates were similar in FHR and control subjects. PTH or calcium infusion did not significantly alter salivary phosphate concentration or clearance rates in either patients or controls. We concluded that untreated FHR patients exhibit a state of mild secondary hyperparathyroidism and an at least normal renal phosphaturic response to PTH. In addition, there is no evidence for increased salivary phosphate excretion in FHR.