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.

Growth hormone deficiency in autoimmune polyglandular disease type 1

This is a case report of 2 patients who were diagnosed to have autoimmune polyglandular disease type 1. Both developed mucocutaneous candidiasis, hypoparathyroidism, vitiligo, and adrenocortical insufficiency. Both were noticed to have subnormal linear growth velocity and delayed bone age. Both showed subnormal stimulated serum growth hormone values indicating growth hormone deficiency. The first case showed favorable response to growth hormone therapy.

Primary infantile hypomagnesaemia: outcome after 21 years and treatment with continuous nocturnal nasogastric magnesium infusion

Primary infantile hypomagnesaemia is an infrequent cause of neonatal hypocalcaemic seizures but one that responds well to magnesium supplementation. We describe a 22-year-old male, first reported at 4 months of age, who is currently free of neurological deficit but has suffered from intermittent hypomagnesaemic tetany and chronic diarrhoea due to large oral magnesium supplements. Hypothesizing that modest hypercalcaemia might prevent the tetany, we conducted a trial of 5 microg/day 1,25(OH)2D3 over 5 days. Despite the resultant increase in calcium, he developed tetany with the reduction of magnesium intake and decline of serum magnesium from 0.63 to 0.39 mmol/l (normal >0.65 mmol/l). After 1,25(OH)2D3 was stopped and the parenteral magnesium injections suspended, 33% of his usual oral supplement was given instead by continuous nasogastric infusion and serum magnesium rose to 0.60 mmol/l. This regimen was better tolerated because of decreased gastrointestinal side-effects and freedom from parenteral injections. We observed that 1,25(OH)2D3 supplements do not promote magnesium retention nor does the resultant hypercalcaemia prevent hypomagnesaemic tetany.

CONCLUSION

Continuous nocturnal nasogastric infusion may be considered in lieu of parenteral therapy in primary infantile hypomagnesaemia.

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.

Observer reliability in grading nephrocalcinosis on ultrasound examinations in children

BACKGROUND

Nephrocalcinosis is often associated with a variety of hypercalcemic conditions. Diagnostic ultrasound is often used for assessing nephrocalcinosis in children, but its reliability has not been proven.

OBJECTIVE

To determine the reliability of expert interpretation of sonographic films with a grading scale of severity for nephrocalcinosis.

MATERIALS AND METHODS

Fifty-eight ultrasonographic films of 30 children with Williams syndrome and other conditions know to be associated with nephrocalcinosis were assessed. We used a blinded randomized design to assess intra- and interobserver reliability.

RESULTS

Grades I, II, and III nephrocalcinosis were noted in 13 %, 19 %, and 27 % of the examinations, respectively. The weighted kappa coefficient was 0.80 (standard error 0.12; 95 % confidence interval 0.68-0.92) for intraobserver agreement and 0.76 (standard error 0.13; 95 % confidence interval 0.63 to 0.89) for interobserver agreement. Reliability in assessing change from one examination to the next, with independently graded films, was fair with an unweighted kappa coefficient of 0.68 (95 % confidence interval 0.38-0.96) and 0.51 (95 % confidence interval 0.21-0.80) for intra- and interobserver reliability, respectively.

CONCLUSION

The severity of nephrocalcinosis can be reliably interpreted with an ultrasonography grading scale.

Asymmetric medullary nephrocalcinosis in two children

Medullary nephrocalcinosis (MNC) is usually a bilateral process with symmetric involvement of both kidneys. Asymmetric medullary nephrocalcinosis has been previously reported in the literature, but has not been well illustrated or explained. We report the sonographic findings in two pediatric patients with hypercalcemia. In both patients an unrelated unilateral renal abnormality, (renal vein thrombosis in one and obstructive hydronephrosis in the other) prevented the development of MNC in the affected kidney, probably by decreasing the glomerular filtration rate and/or altering the renal tubular function.

Renal tubular acidosis and osteopetrosis with carbonic anhydrase II deficiency: pathogenesis of impaired acidification

Renal tubular acidosis with osteopetrosis is an autosomal recessive disorder due to deficiency of carbonic anhydrase II (CAII). A 3.5-year-old Egyptian boy with osteopetrosis and cerebral calcification has a persistent normal anion gap type of metabolic acidosis (plasma pH 7.26) and a mild degree of hypokalemia. A baseline urine pH was 7.0; ammonium (NH4+) excretion was low at 11 mumol/min per 1.73 m2; fractional excretion of bicarbonate HCO3 (FEHCO3) was high at 9% when plasma HCO3 was 20 mmol/l; citrate excretion rate was high for the degree of acidosis at 0.35 mmol/mmol creatinine. Intravenous administration of sodium bicarbonate led to a urine pH of 7.6, a FEHCO3 of 14%, a urine-blood PCO2 difference of 7 mmHg, NH4+ excretion fell to close to nil, and citrate excretion remained at 0.38 mmol/mmol creatinine. Intravenous administration of arginine hydrochloride caused the urine pH to fall to 5.8, the FEHCO3 to fall to 0, the NH4+ excretion rate to rise to 43 mumol/min per 1.73 m2, and citrate excretion to fall to < 0.01 mmol/mmol creatinine. These results show that our patient had a low rate of NH4+ excretion, a low urine minus blood PCO2 difference in alkaline urine, and a low urinary citrate excretion, but only when he was severely acidotic. He failed to achieve a maximally low urine pH. These findings indicate that his renal acidification mechanisms were impaired in both the proximal and distal tubule, the result of his CAII deficiency.

A new classification for renal defects in net acid excretion

The traditional classification of the group of disorders called renal tubular acidosis (RTA) into proximal and distal subclasses is based on which nephron segment is thought to have an abnormal function. Nevertheless, such a distinction may not be correct and also does not characterize the pathophysiology of the renal acidosis in each patient. In this article, we propose an alternative classification, one that is based on the component of net acid excretion that is abnormal. We also suggest expanding the definition of net acid excretion to include a term that describes the renal handling of metabolizable organic anions because their loss in the urine represents the loss of "potential bicarbonate." Because a low rate of excretion of ammonium (NH4+) is present in patients with both distal and isolated proximal RTA, our initial clinical step in patients with hyperchloremic metabolic acidosis (HCMA) is to evaluate the rate of excretion of NH4+. The basis for a low rate of excretion of NH4+ is shown by examining the urine pH. If the urine pH is low, further studies are performed to determine why the availability of NH3 is low; if the urine pH is high, further investigations are initiated to examine if the defect in H+ secretion involves the proximal or the distal nephron. Conversely, if the rate of excretion of NH4+ is high in a patient with HCMA, a component of the degree of acidosis could be attributable to a high rate of excretion of metabolizable organic anions. Case examples are provided to illustrate the approach and its implications for future molecular studies.

Primary hyperparathyroidism in a paediatric hospital

We retrospectively reviewed the presentation and management of children with primary hyperparathyroidism (PHPT) from 1973 to 1995 at a paediatric tertiary-care centre. There were 11 patients (6 females), aged 12.3-17.7 years at presentation, with sporadic PHPT confirmed by histopathology (single adenoma). Presentation consisted of renal colic, or non-specific gastrointestinal, musculoskeletal or neurological symptoms. Misdiagnosis was common until hypercalcaemia was identified, 0.5-24 months after onset of symptoms (mean 7.7 months). All patients had hypercalcaemia and low-normal serum phosphate. The parathyroid hormone (PTH) radioimmunoassay used before 1986 was elevated in 1/4 patients; the intact PTH assay used after 1986 was elevated in 7/7 patients. At presentation, six had end-organ damage: band keratopathy, renal lesions, and/or bone disease. Preoperative localization was accurate in 0/4 patients diagnosed before 1986, but 5/7 patients diagnosed after 1986: three by ultrasound or sestamibi scan alone, and two by ultrasound and technetium scan. Surgical outcome was not dependent upon the accuracy of pre-operative localization. PHPT is rare in children but usually associated with end-organ damage, presumably due to delayed diagnosis. It should be considered in the differential diagnosis of unexplained non-specific complaints. The intact PTH assay greatly assists pre-operative diagnosis. The usefulness of pre-operative localization requires further research.

Constitutively activated receptors for parathyroid hormone and parathyroid hormone-related peptide in Jansen's metaphyseal chondrodysplasia

BACKGROUND

An activating mutation of the receptor for parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) was recently found in a patient with Jansens's metaphyseal chondrodysplasia, a rare form of short-limbed dwarfism associated with hypercalcemia and normal or low serum concentrations of the two hormones. To investigate this and other activating mutations and to refine the classification of this unusual disorder, we analyzed genomic DNA from six additional patients with Jansen's disease.

METHODS

Exons encoding the PTH-PTHrP receptor were amplified by the polymerase chain reaction (PCR), and the products were analyzed by gel electrophoresis or direct nucleotide-sequence analysis. Nucleotide changes were confirmed by restriction-enzyme digestion of genomic DNA or the PCR products.

RESULTS

The previously reported mutation, which changes a histidine at position 223 to arginine (H223R), was found in genomic DNA from three of the six patients but not in DNA from their healthy relatives or 45 unrelated normal subjects. A novel missense mutation that changes a threonine in the receptor's sixth membrane-spanning region to proline (T410P) was identified in another patient but not in 62 normal subjects. In two patients with radiologic evidence of Jansen's metaphyseal chondrodysplasia but less severe hypercalcemia, no receptor mutations were detected. In COS-7 cels expressing PTH-PTHrP receptors with the T410P or H223R mutation, basal cyclic AMP accumulation was four to six times higher than in cells expressing wild-type receptors.

CONCLUSIONS

The expression of constitutively active PTH-PTHrp receptors in kidney, bone, and growth-plate chondrocytes provides a plausible genetic explanation for mineral-ion abnormalities and metaphyseal changes in patients with Jansen's disease.

Bone mass and soft tissue composition in adolescents with anorexia nervosa

The relationship between bone mass and compartments of soft tissue was studied in 22 adolescent women with anorexia nervosa (mean, 17 years). Results were compared to data on age- and gender-matched controls. Bone mass of the lumbar vertebrae and femoral neck, fat and lean tissue was measured by dual energy X-ray absorptiometry (DXA). Bone mass in the central third of the skeleton, by neutron activation analysis (NAA), and body protein, by prompt gamma ray analysis (PGA), was measured on patients, but not controls. The patients had significantly lower values than controls in total weight (26%), lean tissue (16%), fat (60%), bone mass of lumbar spine (14%), and femoral neck (15%). The mean calcium bone index (CaBI), the central skeletal calcium normalized for body size based on height, was significantly lower than the value for external controls, (0.86 +/- 0.10 vs. 0.97 +/- 0.10). The nitrogen index (NI), body protein normalized for height, showed a similar reduction from external controls (0.84 +/- 0.10 vs. 1.0 +/- 0.10). Bone mass (both DXA and NAA data) was strongly correlated to lean tissue and to protein; the correlations to fat were weaker. Follow-up studies after 7-26 months in 12 patients showed a modest increase in weight (mean, 4.9 kg) which was due, primarily, to an increase in fat with only insignificant increase in lean tissue and in protein. In bone mass, there was either no change or further loss. Only four restored body weight to normal (BMI > 20) and they achieved normal menstruation, but even these four responders showed no increase in bone mass. Our studies confirm that adolescent females with anorexia nervosa suffer losses not only in all compartments of body composition, but also demonstrate that the restoration of bone mass lags behind improvement in soft tissue compartments. These results were independent of methods used for the measurements.

Persistence of Vitamin D-deficiency rickets in Toronto in the 1990s

To assess the current picture of vitamin D deficiency, we reviewed all 17 cases of vitamin D-deficiency rikets seen in the referral clinic of a children's hospital in Toronto between 1988 and 1993. The diagnosis was made at 7 to 33 months of age. All the children were symptomatic all had biochemical and radiographic abnormalities, two suffered hypocalcemic seizures, and all had bowing of the extremities. Twelve of the children were born to parents who were recent immigrants to Canada. All were of Asian or African origin with dark skin. All the children had been exclusively breastfed with no vitamin D supplementation, and had had little or no sunlight exposure. All the patients responded to vitamin D therapy. We conclude that vitamin D-deficiency rickets remains an environmental/nutritional deficiency disease in this city and that efforts at prevention should target children with pigmented skin from families who are recent immigrants.

Bone mass in children with congenital hypothyroidism treated with thyroxine since birth

To determine whether the large doses of thyroxine treatment early in life adversely affect bone mass, we measured bone mass of 20 congenital hypothyroid (CH) patients (8.4 +/- 2.2 years) who were diagnosed and treated since birth. Starting thyroxine dose and current dose were 8.5 +/- 1.9 micrograms/kg/day and 3.1 + 1.2 micrograms/kg/day respectively. Thyroid function and serum biochemical tests for calcium homeostasis were normal at the time of study. Bone mass was measured by dual energy X-ray absorptiometry. Nine siblings served as controls. The patients' bone mineral density was within the normal range of population controls, and was not different from the sibling controls. The patients also had height-adjusted bone mineral content equal to the expected height-adjusted values in the siblings. Our studies indicate that the large doses of thyroxine therapy for CH do not cause osteopenia in childhood.

Normal parathyroid hormone responsiveness of bone-derived cells from a patient with pseudohypoparathyroidism

Pseudohypoparathyroidism (PHP) is characterized by a lack of response to parathyroid hormone (PTH); however, normal skeletal responsiveness to PTH in some patients with PHP type Ia was previously suggested on the basis of clinical observations. To test this hypothesis, we measured cyclic adenosine monophosphate (cAMP) production in response to various agonists in bone-derived osteoblast-like (OBL) cells from trabecular explants obtained from an iliac crest biopsy of a 25-year-old woman with PHP. The patient was proved to have PHP type Ia on the basis of Albright's hereditary osteodystrophy and decreased activity of stimulatory guanine nucleotide-binding protein (Gs) in erythrocytes. Responsiveness of the patient's OBL cells was compared with OBL cells from eight subjects aged 18-39 years who had no evidence of metabolic bone disease. OBL cells from the patient responded to the following agonists (expressed in multiples of elevation of cAMP, stimulated/basal, mean +/- SE, n = 3): PTH, 3.8 +/- 0.3; forskolin, 8.2 +/- 0.2; and cholera toxin, 56.8 +/- 10.0. These responses were not significantly different from those of control OBL cells: PTH, 4.5 +/- 1.1 (range 2.4-7.5); forskolin, 7.7 +/- 1.4; and cholera toxin, 57.9 +/- 16.2. The normal cholera toxin response indicated the presence of functional Gs. Bone cells from patients with PHP type Ia may exhibit a normal PTH receptor-coupled adenylyl cyclase system in vitro despite clinical evidence of impaired hormone-responsive adenylyl cyclase in other tissues, including the kidney. Skeletal responsiveness to PTH may explain the long periods of spontaneous normocalcemia observed in this patient.

Hypoparathyroidism associated with systemic lupus erythematosus

We describe a 15-year-old girl with systemic lupus erythematosus (SLE) who presented with hypocalcemia and a generalized seizure in the setting of an intercurrent illness and active central nervous system lupus. She was subsequently found to have idiopathic hypoparathyroidism. The association of SLE with hypoparathyroidism is extremely rare and this case represents the first pediatric report of this rare association. We suggest there may be a common underlying pathophysiological process linking these diseases.

The value and limitation of dual-energy X-ray absorptiometry

In population studies, in which patients and controls are of comparable size, bone mineral area density (BMD) gives reliable results for mean bone mass data although, with sequential data, BMD may under-estimate the degree of change in bone mass. In children BMD data should be reliable, provided that patients and controls, matched for age and sex, are also of the same size. With disease children may be small for their age so that low bone mass by BMD may be due to small body size and not necessarily to osteopoenia. In these situations the bone mineral content (BMC) index may be more reliable than BMD. To assess bone mass status in individuals, BMC index, as well as BMD, should be used, particularly with adults at the extremes of body size (the very small or very tall).

Nephrocalcinosis and nephrolithiasis due to subcutaneous fat necrosis with hypercalcemia in two full-term asphyxiated neonates: sonographic findings

Subcutaneous fat necrosis leading to hypercalcemia is rare but well documented in asphyxiated neonates. This paper presents two such neonates in whom sonography revealed the development of nephrocalcinosis and nephrolithiasis. The kidneys had initially been shown to be normal sonographically. In one infant, nephrocalcinosis developed as increasing echogenicity of the medullary pyramids. In the other, increased echogenicity of the renal cortex of uncertain cause developed together with nephrolithiasis. These sonographic appearances have not been described previously in this entity.

Comparisons between oral and intraperitoneal 1,25-dihydroxyvitamin D3 therapy in children treated with peritoneal dialysis

Recent studies in adults have suggested that parenteral 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) may have advantages over oral therapy in the management of renal osteodystrophy. The purpose of this study was to determine whether there were clear differences between oral and IP 1,25(OH)2D3 treatments in children who did not pose a treatment problem. Seven children (5 males, 2 females, aged 1.8 to 16 years, median 4.8 years) undergoing peritoneal dialysis were initially treated with oral 1,25(OH)2D3 for a one month equilibration period They were randomly assigned to 3 months of either oral or intraperitoneal (IP) therapy with 1,25(OH)2D3 followed by 3-months-treatment using the alternative route. No significant differences in serum creatinine, phosphate, or parathyroid hormone concentrations were found between the different routes of administration in the patients. No significant differences in height standard deviation scores or renal osteodystrophy scores were found over the six-month study. Paired oral and IP pharmacokinetic studies were performed on these 7 patients and 2 other children who had been treated for at least 2 months using either oral or IP 1,25(OH)2D3. Serum was taken prior to one of the usual 1,25(OH)2D3 doses and 0.5, 1.5, 3, 6, and 24 h afterward. The highest measured concentrations of 1,25(OH)2D3 were found at 1.5 h for both oral and IP treatments (mean Cmax [SD]: oral 116 [23] pmol/l, IP 121 [24] pmol/l, p > 0.05). The AUC's for oral and IP therapy were similar (1701 [276] and 1645 [301] pmol/h/l, respectively). In the paired pharmacokinetic studies no significant differences were found between oral and IP treatments for the serum half life (27.4 [11.6] h and 19.2 [8.1] h, respectively) and total body clearance (15.3 [2.1] h and 18.4 [3.3] h, respectively) of 1,25(OH)2D3. In children who respond appropriately to oral 1,25(OH)2D3 there is no biological advantage to the use of IP 1,25(OH)2D3.

Nephrocalcinosis in X-linked hypophosphataemic rickets: its relationship to treatment, kidney function, and growth

We studied 25 patients treated with oral phosphate and 1,25(OH)2 vitamin D for 0.5-15 y (mean, 7 y) to determine the incidence of nephrocalcinosis and its relationship to treatment, renal function, and growth. During the follow-up period, 3 hypercalcaemic and 13 random hypercalciuric episodes were documented. Creatinine clearances and urine concentration tests were normal in all patients. One patient's 24-h urine specimen indicated hypercalciuria. Kidney ultrasonography revealed nephrocalcinosis in 80% of the patients, but its severity was not significantly related to the dose of calcitriol or of phosphate, the duration of treatment, the age at which treatment was started, or growth. None of the 9 untreated affected family members had nephrocalcinosis. Longitudinal studies revealed that the greatest loss in height velocity occurred during the first 2 y of life. Our study shows that nephrocalcinosis is a common complication of phosphate and 1,25(OH)2D3 treatment, but it is not necessarily associated with impaired renal function. Although the treatment failed to prevent a decrease in height velocity during infancy, it effectively maintained height velocity after 2 y of age.

Refining the genetic map for the region flanking the X-linked hypophosphataemic rickets locus (Xp22.1-22.2)

We have screened fourteen kindreds with X-linked hypophosphataemic rickets with four microsatellite markers, viz AFM163yh2, DXS999 (AFM234yf12), DXS443 and DXS365, in order to refine the genetic map flanking the gene, and to define a close flanking interval for the construction of a yeast artificial chromosome (YAC) and cosmid contig. The genetic data were enhanced after the isolation of a large 1.2-megabase YAC derived from AFM163yh2, in which marker DXS274 was present but not DXS365 or DXS443. Against HYP, DXS365, AFM163yh2 and DXS443 showed no recombinants (Zmax = 18.1, Zmax = 9.9, and Zmax = 16.0 respectively). DXS999 gave Zmax = 9.6 at 4% recombination and lies distal to HYP but proximal to DXS197 and DXS43. The disease gene and markers AFM163yh2 and DXS365 are flanked by DXS443 and DXS274. Combining the genetic and physical data, we are able to propose the following gene marker order: Xptel-DXS43-DXS197-DXS999-DXS443-[(DXS3 65-AFM163yh2), HYP]-DXS274-DXS41-Xcen.

Partial hypoparathyroidism. A variant of transient congenital hypoparathyroidism

We encountered three children who had neonatal hypocalcemia followed by a period of normocalcemia and recurrence of hypocalcemia later in childhood. They were full-term infants with normal birth weights who developed hypocalcemia within the first 48 hours after birth. The hypocalcemia resolved in 1 week, 3 months, and 14 months in the three patients. The recurrences of hypocalcemia occurred at 4, 7, and 12 years of age. Their plasma parathyroid hormone concentrations were consistently low but detectable. We suggest that partial hypoparathyroidism is the underlying abnormality in these patients and that neonatal hypocalcemia in otherwise healthy infants indicates the need for calcium measurements during childhood and adolescence.

Tracer kinetics and actions of oral and intraperitoneal 1,25-dihydroxyvitamin D3 administration in rats

Tracer kinetic parameters of [3H]-1,25(OH)2D3 were calculated from data obtained following its acute oral (p.o.) or intraperitoneal (i.p.) administration. In normal rats studied after the tracer had distributed into the body, the slope and intercept of the log-serum [3H]-1,25(OH)2D3 versus time relationship were not significantly influenced by the route of administration. Pretreatment with 1,25(OH)2D3 (0.2 micrograms/100 g/day) by the same route as the tracer resulted in the following changes: in p.o. rats the serum [3H]-1,25(OH)2D3 intercept was much lower but the slope was not changed; in i.p. rats the intercept was not changed but the slope was increased. Both p.o. and i.p. treatment with 1,25(OH)2D3 lowered the weight gain and diet consumption, and increased serum calcium, kidney tissue calcium and urinary excretion of orally administered 45Ca. All the measures of bioactivity were greater in the i.p. dosed rats than in the p.o. dosed rats. We conclude that the p.o. 1,25(OH)2D3 was less potent because of diminished bioavailability due to self induction of its presystemic metabolism and inactivation.

Hypercalcemia in infants presenting with apnea

To our knowledge apnea in infants has not been associated with hypercalcemia. We describe seven hypercalcemic infants aged 2 days to 3 months who had presented with apnea; six of the seven were otherwise healthy. The apneic attacks were brief, and normal breathing was restored spontaneously or after tactile stimulation. The attacks stopped and the apnea monitoring was discontinued when the children were 1 month to 2 years of age. The only abnormal finding common to all of the patients was hypercalcemia. Idiopathic infantile hypercalcemia was diagnosed in six of the patients and familial benign hypercalcemia in one. Our findings suggest that determination of the plasma calcium level be included in the investigation of apnea in infancy.

Ultraviolet irradiation for hepatic rickets

An infant with chronic cytomegalovirus hepatitis and a child with atypical Alagille's syndrome had vitamin D deficiency rickets due to malabsorption. Both received ultraviolet irradiation. This treatment corrected biochemical abnormalities and healed the rickets. In the infant use of a sunlamp at home maintained normal 25 hydroxy-vitamin D for over a year. Our study shows that ultraviolet irradiation is an effective treatment of hepatobiliary rickets.

Effects of acute carbon tetrachloride poisoning on vitamin D3 metabolism in the rat

To achieve biologic potency, vitamin D must undergo two successive hydroxylations, first, in the liver and then, in the kidney. Carbon tetrachloride is known to cause extensive damage to the liver, but its effect on vitamin D metabolism has not been studied thoroughly. The effect of carbon tetrachloride on renal hydroxylation of 25-hydroxyvitamin D3 has not been studied. To evaluate the acute effect of carbon tetrachloride on vitamin D metabolism in the liver, vitamin D depleted rats received a single intraperitoneal injection of carbon tetrachloride (2.0 mL/kg body weight). After 24 h, they were given 55, 550, or 5050 pmol [3H]vitamin D3 intravenously. Twenty-four hours after injection of [3H]vitamin D3, aliquots of serum and liver were analyzed for [3H]vitamin D3 and its metabolites by high performance liquid chromatography. Sera of carbon tetrachloride treated rats had higher [3H]vitamin D3 and [3H]25-hydroxyvitamin D and lower [3H]1,25-dihydroxyvitamin D3 concentrations than did control sera. Livers of carbon tetrachloride treated rats contained more [3H]vitamin D3, [3H]25-hydroxyvitamin D3, and more fat. Liver histology showed massive centrilobular necrosis in the treated rats. Thus, our experiment in rats given an acute dose of carbon tetrachloride provided no evidence of impairment of vitamin D metabolism by the liver, but offered a suggestion that 25-hydroxyvitamin D3 metabolism by the kidney might be impaired. To determine the acute effect of carbon tetrachloride on metabolism of vitamin D3 by the kidney, we studied hydroxylation of [3H]25-hydroxyvitamin D3 in isolated perfused kidney. Kidneys from the treated rats showed a 66% reduction in [3H]1,25-dihydroxyvitamin D3 production.

Differential behaviour of 25-hydroxyvitamin D3 24-hydroxylase and 1-hydroxylase in response to protein synthesis inhibitors and cytochrome P-450 inhibitors

To characterize 25-hydroxyvitamin D3 24-hydroxylase and 25-hydroxyvitamin D3 1-hydroxylase, the activities of the two enzymes were measured in the presence of two types of inhibitors. The effect of protein synthesis inhibitors on 25-hydroxyvitamin D3-stimulated 24-hydroxylase activity in 1-hydroxylating rat kidneys perfused in vitro was tested. Actinomycin D (4 microM) and cycloheximide (10 microM) each abolished 25-hydroxyvitamin D3 24-hydroxylase synthesis when added at the start of perfusion but not when added 4 h later; they did not affect 25-hydroxyvitamin D3 1-hydroxylase activity. The effects of cytochrome P-450 inhibitors on the two enzyme activities were then studied in vivo. Metyrapone and SKF-525A (50 mg/kg body weight) each inhibited 25-hydroxyvitamin D3 24-hydroxylase at 6 and 24 h; in contrast 1-hydroxylase increased and was 5 times the control value at 24 h. Finally, the in vitro effects of six cytochrome P-450 inhibitors at concentrations ranging from 10(-7) to 10(-3) M on enzyme activities in renal mitochondrial preparations were compared. Both enzymes were inhibited by all of the inhibitors, but inhibition of 25-hydroxyvitamin D3 24-hydroxylase was consistently greater than that of 25-hydroxyvitamin D3 1-hydroxylase. These studies demonstrate that 24-hydroxylation and 1-hydroxylation respond differently to protein synthesis inhibitors and to cytochrome P-450 inhibitors. The findings are consistent with the hypothesis that the two enzyme activities are associated with different cytochrome P-450 moieties.

Low dietary calcium reduces 25-hydroxycholecalciferol in plasma of rats

We investigated whether dietary factors that are known to increase 1,25-(OH)2-cholecalciferol production can deplete plasma 25-OH-cholecalciferol. Plasma concentration of 25-OH-cholecalciferol, its metabolism in vivo and activities of renal mitochondrial 25-OH-cholecalciferol 1-hydroxylase (1-OHase) and 25-OH-cholecalciferol 24-hydroxylase (24-OHase) were measured in rats fed various amounts of calcium (Ca) and phosphorus (P). All diets contained 5 micrograms (200 IU) cholecalciferol per 100 g. For rats fed the "normal" diet (0.7% Ca and 1.2% P) the mean plasma 25-OH-cholecalciferol level was 11.0 +/- 0.8 nmol/L, and the mean 1-OHase activity was 30 +/- 5 fmol/(mg X min). All rats fed the low Ca (0.014%) diet had 1-OHase activities above 200 fmol/(mg X min) and undetectable plasma 25-OH-cholecalciferol levels (less than 2.5 nmol/L). The chi-square test interrelating plasma 25-OH-cholecalciferol and dietary Ca showed statistical significance (P less than 0.001). The high activity of 1-OHase that resulted from dietary Ca restriction increased utilization of 25-OH-cholecalciferol to the point of causing depletion of this metabolite in the circulation.

Keratitis associated with the multiple endocrine deficiency, autoimmune disease, and candidiasis syndrome

Optimal management of the ocular and systemic components of the multiple endocrine deficiency, autoimmune disease, candidiasis syndrome requires early identification of affected individuals. This autosomal recessive syndrome is characterized by hypoparathyroidism, Addison's disease, and chronic mucocutaneous candidiasis among other endocrinopathies and immune disorders. We retrospectively reviewed 16 patients, 14 with the full syndrome and two with the syndrome partially manifested. Four of these patients manifested a self-limited, bilateral keratitis in which the age of onset ranged from 2 to 9 years. Keratitis preceded the onset of any endocrinopathy in two of four patients and was among the first signs of the syndrome. The keratitis was not caused by hypoparathyroidism or candidiasis. The anterior stromal vascularization and scarring resulted in a visual acuity of 20/50 or worse in four of eight affected eyes. We recommend medical management of the corneal disease without surgical intervention.

Renal osteodystrophy in children undergoing continuous ambulatory peritoneal dialysis

Fifteen children undergoing continuous ambulatory peritoneal dialysis for 0.3 to 2.4 years were evaluated longitudinally for renal osteodystrophy. Immunoreactive parathyroid hormone, 25-OHD, total and ionized calcium, inorganic phosphate, and alkaline phosphatase levels were measured regularly. Skeletal radiographic studies were performed at the onset and conclusion of CAPD and at six-month intervals during therapy. All children received 1,25(OH)2D3 and aluminum hydroxide, and nine received supplemental calcium. Plasma 25-OHD concentrations were normal to elevated, and calcium increased steadily to high normal levels despite a trend to persistent hyperphosphatemia. The increased calcium levels suppressed parathyroid hormone overactivity in only one patient. At the onset of CAPD, nine patients had hyperparathyroid bone disease seen radiographically, three of whom also had rachitic lesions. At the end of CAPD, the hyperparathyroid lesions had improved in four patients, completely resolved in three, and deteriorated in two. Rachitic lesions had completely healed in two patients and improved in the third. However, among the six children without radiographically evident lesions at onset of CAPD, hyperparathyroid bone lesions developed in two and rachitic lesions in two others during CAPD. Although CAPD and appropriate therapy benefited most patients with renal osteodystrophy, the benefits were not uniform, and bone lesions deteriorated in some.

Stimulation of 24R,25-dihydroxyvitamin D3 synthesis by metabolites of vitamin D3

Previously we have shown that the isolated perfused kidney from vitamin D-deficient rats converts [3H]25(OH)D3 into [3H]1 alpha,25(OH)2D3. When certain vitamin D metabolites were added to perfusate the same kidney began to synthesize [3H]24R,25(OH)2D3. In this study we investigated the structural requirements of the vitamin D molecule necessary to stimulate synthesis of [3H]24R,25(OH)2D3 in a 1-hydroxylating kidney. Kidneys were perfused with tracer [3H]25(OH)D3 (450 pM) alone and in the presence of a variety of hydroxylated metabolites and fluorinated analogues of vitamin D3 at concentrations of 450 pM to 25 microM. Tracer [3H]25(OH)D3 alone resulted in synthesis of only [3H]1 alpha,25(OH)2D3 during the 6-h perfusion period. 25-Hydroxylated metabolites [25(OH)D3, 25 nM; 1 alpha,25(OH)2D3, 25 nM; 24R,25(OH)2D3, 25 nM; 24(F)2,25(OH)D3, 50 nM] stimulated [3H]24R,25(OH)2D3 production at 2 h of perfusion. On the other hand, analogues without the 25-hydroxyl group [D3; 1 alpha(OH)D3; 25(F)D3; 1 alpha(OH),25(F)D3; 1 alpha(F)D3; 1 beta(F)D3]; did not stimulate [3H]24R,25(OH)2D3 synthesis. We conclude that the 25-hydroxyl group is an essential determinant of 24-hydroxylation.

Renal osteodystrophy in children with chronic renal failure: an unexpectedly common and incapactating complication

The incidence, age at onset, and progression of the biochemical, radiographic, and histologic characteristics of renal osteodystrophy were studied in 50 children in whom chronic renal failure had been recently diagnosed. During a ten-year observation period, 19 patients progressed to end-stage renal failure and radiographic signs of renal osteodystrophy developed in 15 of these (79%). Renal osteodystrophy developed in all nine patients whose chronic renal failure was diagnosed before 3 years of age and in six of the ten children with later onset of failure. The mean interval from diagnosis of renal failure to development of osteodystrophy was 1.4 years. Radiographically, growth zone lesions predominated in the younger children, whereas cortical erosions were more prevalent in the older children. Histologic examination, performed in 38 patients, showed both defective mineralization and excessive resorption and was a more sensitive diagnostic index than radiography. Noticeable deformities developed in one third of the patients with osteodystrophy, despite medical treatment including vitamin D2 therapy. Deformities were particularly frequent and severe in patients whose renal failure developed in infancy. In all 13 patients whose growth patterns were studied before and after osteodystrophy developed, the onset of bone lesions was associated with a deterioration of growth, indicating that osteodystrophy plays a major role in causing the growth retardation commonly observed in children with chronic renal failure.

Inhibition of 25-hydroxyvitamin D3-1-hydroxylase by chronic metabolic acidosis

Chronic metabolic acidosis had been shown to influence the renal metabolism of 25-hydroxyvitamin D3. Using the isolated perfused rat kidney model, we evaluated the rates of synthesis of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in vitamin D-depleted [D(-)] and 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] in vitamin D-replete [D(+)] rats. Metabolic acidosis was induced in both groups of rats by feeding aqueous ammonium chloride for 9 days. Kidneys isolated from D(-) acidotic rats (mean pH, 7.11) exhibited a decreased rate of 1,25(OH)2D3 synthesis (0.79 +/- 0.17 pmol produce . h-1 . g kidney-1) when compared with that (1.27 +/- 0.09) of D(-) nonacidotic (mean pH, 7.33) rats. There was a significant negative linear correlation between the rate of synthesis of 1,25(OH)2D3 and the hydrogen ion concentration of the animal (r = 0.79, P less than 0.005). The rate of synthesis of 24,25(OH)2D3 by the kidneys from D(+) acidotic (mean pH, 7.06) and nonacidotic (mean pH, 7.39) rats did not differ (0.81 +/- 0.21 vs. 0.60 +/- 0.12 pmol product . h-1 . g kidney-1). It is concluded that chronic acidosis suppressed 1-hydroxylase activity, but does not suppress 24-hydroxylase activity.

Hypoparathyroidism and pseudohypoparathyroidism in childhood

Although relatively uncommon, the conditions of hypoparathyroidism and pseudohypoparathyroidism in childhood provide an exciting diagnostic and therapeutic challenge. Knowledge of calcium-phosphate homeostasis has progressed rapidly over the past few years so that our understanding of the basic pathophysiological mechanisms has increased tremendously. However, further clinical and basic scientific research will, no doubt, unravel further variations of the various disease entities described.

Parathyroid hormone responsiveness in the sheep fetus and newborn lamb

Responsiveness of the sheep fetus to parathyroid hormone (PTH) infusion was studied in the unanesthetized fetus in situ and the results were compared with those obtained in the newborn lamb, PTH, 0.5 USP U/min per kilogram body weight was infused intravenously to four sheep fetuses in utero (gestational age 127-141 days) and 10 newborn lambs (1-20 days of age). PTH infusion increased plasma Ca in the fetus and the PTH-induced hypercalcemia increased plasma calcitonin although the maternal levels of Ca and calcitonin did not change. In the fetus, as well as in the newborn lamb, PTH decreased the percentage tubular reabsorption of phosphate (TRP) and increased urinary excretion of cAMP. These results indicate that the sheep fetus has developed the target organ responsiveness to PTH and a normal calcitonin secretory mechanism by the last trimester of gestation.

25-hydroxyvitamin D3 metabolism by isolated perfused rat kidney

Kidneys of adult rats were removed and perfused with semisynthetic media with the object of elucidating the separate actions of factors implicated as modulators of renal metabolism of 25-hydroxyvitamin D3 (25(OH)D3). During a 3-h perfusion with 3[H]25(OH)D3, the kidney produced high yields of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) or 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) depending on whether the rat had previously been, respectively, normocalcemic, normophosphatemic, vitamin D-replete or hypocalcemic, hypophosphatemic, vitamin D-deplete. With longer perfusion (up to 12 h), kidneys from normocalcemic, normophosphatemic, vitamin D-replete rats mainly produced 24,25(OH)2D3 but also amounts of 1,25(OH)2D3. This pattern was unaltered by reducing Ca or Pi concentrations of perfusate or by adding parathyroid hormone. Kidneys of hypocalcemic, hypophosphatemic, vitamin D-deplete rats perfused with low Ca, low Pi medium for 12 h at first produced 1,25(OH)2D3 exclusively. However, 24,25(OH)2D3 appeared after 4 h and accumulated thereafter, whereas 1,25(OH)2D3 synthesis ceased after 7 h, a metabolic pattern unaffected by the concentration of substrate or end products in the perfusate or by addition of cyclic AMP. The model shows promise for studying regulation of 25(OH)D3 metabolism by the kidney.

25-hydroxyvitamin D metabolism in the sheep fetus and lamb

The metabolism of [3H]-25-hydroxyvitamin D3(3H-25-OH-D3) to [3H]-1,25-dihydroxyvitamin D3 (3H-1,25-(OH)2D)3 and [3H]24, 325 dihydroxyvitamin D3 (3H-24,25-(OH)2D3) was studied in sheep fetuses and lambs. In vivo metabolism was observed by chromatography of extracts of plasma obtained 24 hr after direct iv injection of 3H-25-OH-D3 to the fetus and lamb. The renal enzymes 25-hydroxyvitamin D-1-hydroxylase and -24-hydroxylase were determined in vitro by quantitative assay. In fetal lambs, 3H-24,25-(OH)2D3 was consistently the only detectable dihydroxyvitamin D3 metabolite; this was confirmed by the in vitro studies in which 24-hydroxylase was the only detectable enzyme. Parathyroid hormone infusion to the fetus did not stimulate 3H-1,25-(OH)2D3 production. In normal lambs fed sheep's milk or cow's milk 3H-24,25-(OH)2D3 was the only metabolite of 3H-25-OH-D3 in vivo and only 24-hydroxylase activity was detected in vitro. In lambs fed a low-calcium, vitamin D-free formula, 24-hydroxylase activity remained measurable for at least 11 days of feeding, and by that time 1-OHase activity became evident in vitro. Appreciable 3H-1,25-(OH)2D3 was not observed in plasma until 16 days of feeding with the formula. After 18 days on low-calcium, vitamin D-free formula, 1-OHase was the only detectable 25-OH-D3 metabolizing enzyme. We also studied the rates at which 3H-25-OH-D3, 3H-24,25-(OH)2D3 and 3H-1,25-(OH)2D3 disappeared from the lamb plasma compartment. Within 1 hr, 3H-1,25-(OH)2D3 fell to 50% of its initial concentration, and after 72 hr only 2% was left. In the case of 3H-25-OH-D and 3H-24,25-(OH)2D3, 50% of each metabolite was left after 7 to 10 hr and about 20% after 72 hr. The rapid disappearance of 3H-1,25-(OH)2D3 may explain the low levels or absence of this metabolite observed in the plasma of some animals shown to have renal 1-hydroxylase activity.

Pathogenesis of rickets in chronic hepatobiliary disease in children

To investigate whether hepatobiliary rickets is caused by defective intestinal absorption of vitamin D or by impaired hepatic hydroxylation of the vitamin, we studied three children who developed severe rickets, hypocalcemia, and hypophosphatemia, two despite having received 400 to 800 IU vitamin D per day by mouth, and one despite prolonged treatment with 10,000 IU daily. On oral vitamin D therapy, plasma vitamin D and 25-hydroxyvitamin D levels were low. When two children were treated with weekly intravenous doses of 3,000 IU vitamin D to approximate the recommended prophylactic allowance, their plasma calcium and phosphate values improved promptly, the radiographic lesions healed, and the plasma concentrations of vitamin D and 25-hydroxyvitamin D became normal. Our studies indicate that the primary cause of hepatobiliary rickets is intestinal malabsorption of vitamin D, not impairment of the hepatic metabolism of the vitamin.

Vitamin D therapy in hypoparathyroidism and pseudohypoparathyroidism: weight-related dosages for initiation of therapy and maintenance therapy

The aims of this study were to determine the dose of vitamin D2 that maintains the serum calcium level within the normal range in hypoparathyroid and pseudohypoparathyroid children and to establish a safe and quickly acting dose for initiating therapy in symptomatic patients. The dose requirement for maintenance therapy was studied in 11 patients and initiation therapy was studied in five newly diagnosed hypocalcemic patients. The results show that (1) the maintenance requirement of vitamin D2 is proportional to body weight and averages 2,000 IU (50 microgram)/kg/day for children of all ages and with all types of hypoparathyroid disorders and the (2) in newly diagnosed symptomatic patients, carefully controlled administration of 8,000 IU (200 microgram) vitamin D2/kg/day for the first one to two weeks corrects hypocalcemia quickly and safely.

Keratitis with hypoparathyroidism

Chronic kiratitis developed in two children with nonsurgical hypoparathyroidism, as part of an autosomal recessive syndrome that included adrenal insufficiency and moniliasis in what was postulated to be an autoimmune disease. The corneal changes may also have been caused by autoimmune mechanism. Activity of the keratitis diminished once the hypoparathyroidism had been brought under control. However, these patients were thought to be at risk for adrenal insufficiency: neither had moniliasis or adrenocortical insufficiency at present, but the features of the hypoparathyroidism adrenal insufficiency-moniliasis syndrome appeared at different ages and in differing sequences.

Response of protracted neonatal hypocalcaemia to 1alpha,25-dihydroxyvitamin D3

Six infants with protracted hypocalcaemia (5 classed as tetany of the newborn) had a mean plasma-calcium of less than 6-4 mg/dl and raised plasma-inorganic-phosphate. Four had been hypocalcaemic for longer than 2 weeks despite treatment with low phosphate formulae and extra calcium. All the infants were treated with 1alpha,25-dihydroxyvitamin D3 (1alpha,25-(OH)2D3), usually in a dose of 0-05 mug/kg body-weight/day, administered intravenously for 5--12 days. The plasma-calcium levels began to rise within 24 h after starting 1alpha,25-(OH)2D3 treatment, increased above 7-5 mg/dl within 3 days, and reached the normal range within 8 days. Four of the infants remained normocalcaemic when 1alpha,25-(OH)2D3 was discontinued, but two infants became hypocalcaemic again and required long-term treatment. 1alpha,25-(OH)2D3 has been found safe and dependable as treatment for protracted neonatal hypocalcaemia.

Increased bone mineral content in young adults with familial hypophosphatemic vitamin D refractory rickets

Seven adults with familial hypophosphatemia have been investigated by histologic and radiographic examination of bone, and estimates of bone mineral status by in vivo neutron activation analysis (IVNAA). Histological examination showed severe osteomalacia and osteosclerosis in all cases. Radiography showed skeletal deformities and other sequelae of severe rickets of childhood in five of the seven cases, with, in addition, thickened well-mineralized bones; the other two showed normal radiographs. IVNAA measurements showed that the first five had greater than normal bone calcium and that the other two had normal values. Thus, in all cases there is a greater than normal total bone tissue (osteoid and mineralized bone together). The quantitative body calcium measurements show clearly that osteosclerosis occurs in familial hypophosphatemia, confirming the opinions based on histological and radiological data. Although there has been occasional reference to this sclerosis in the literature, up to the present it has received little attention.