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Calcium and phosphate metabolism in children with idiopathic hypoparathyroidism or pseudohypoparathyroidism: Effects of 1,25-dihydroxyvitamin D3
Calcium and phosphate metabolism in children with idiopathic hypoparathyroidism or pseudohypoparathyroidism: Effects of 1,25-dihydroxyvitamin D3 Two children with congenital hypoparathyroidism and two children with pseudohypoparathyroidism were given maintenance doses o f 15 to 45 ng/kg/day 1,25-dihydroxyvitarnin D3for a total o f 255 months. The urinary calcium excretion showed an upward elevation after the first 2 years o f treatment but was not significantly higher than that in 10 normal control subjects. The renal threshold for phosphate excretion stayed within the normal ranges compared with control values. Two hypercalcemic and two hypocalcemic episodes occurred during this period o f treatment. Hypercalcemia was reversed within 1 week after withdrawal o f 1,25-dihydroxyvitamin 193. Hypocalcemia was countered by increasing the dose Of 1,25-dihydroxyvitamin D3. Renal functions were not adversely affected, as estimated by creatinine clearance and reciprocals of serum creatinine concentrations. The mean serum calcium concentration during 1,25-dihydroxyvitamin 1)3 treatment was significantly higher (P = 0.00l~ compared with that obtained during vitamin De treatment at a dose o f 500 to 3000 IU/kg/day. These data provide additional support for the long-term use o f 1,25-dihydroxyvitamin D3 in idiopathic hypoparathyroidism and pseudohypoparathyroidism. (J PEDtATR 106:421, 1985)
James C. M. Chan, M.D., Reuben B. Young, M.D., Michael A. Hartenberg, M.D., and Vernon M. Chinchilli, Ph.D. Richmond,
Virginia
IDIOPATHIC HYPOPARATHYROIDISM ~,2 and pseudohypoparathyroidism3,4 are inherited disorders associated with hypocalcemia, as the result of a congenital deficiency of parathyroid hormone in the former and as a consequence of renal tubular and skeletal resistance to parathyroid hormone in the latter. In hypoparathyroidism the impaired renal hydroxylation of 25-hydroxyvitamin D3 to 1,25From the Departments of Pediatrics, Radiology, and Biostatistics, Medical College o f Virginia; and the Nephrology, GeneticsEndocrine-Metabolism, and Radiology Sections, Children's Medical Center, Virginia Commonwealth University. Supported in part by Grants GCRC R R 0065, R01 A M HD 31370, and R01 A M HD 32431 .from the National Institutes of Health. Submitted for publication June 7, 1984; accepted Aug. 17, 1984. Reprint requests: James C. M. Chan, M.D., Box 498 Medical College of Virginia Station, Richmond, VA 23298.
dihydroxyvitamin D 3 plays an important role in the development of hypocalcemia? ,6 The hypocalcemia of pseudohypoparathyroidism may also be secondary to deficiency of I
cAMP
1,25-dihydroxyvitaminD3 25-hydroxyvitamin D3 TmP/GFR PTH PTE
Cyclic adenosine monophosphate Calcitriol, 1,25-dihydroxycholecalciferol, 1,25-(OH)2-D3, 1,25-D Calcidiol, 25-hydroxych01ecaleiferol, 25-OH-D3 Tubular threshold for phosphate Parathyroid hormone Parathyroid extract
1,25-dihydroxyvitamin D~ associated with parathyroid resistance at the renal tubular sites, 7,8 These observations provide the rationale for the therapeutic use of 1,25dihydroxyvitamin D3 in these disorders. H~
The dournal of P E D I A T R I C S
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422
Chanet al.
The Journalof Pediatrics March 1985
Table. Clinical a n d biochemical d a t a in four adolescents given 1,25-dihydroxyvitamin D3
Ageatstart e ] Sex I Maintenancetherapy of therapy* 1,25-D supplement Patient[ (yr) ]Rae (~g/day) (Po) Idiopathic hypoparathyroidism 1 10.2 W 2 9.0 W Pseudohypoparathyroidism 3 14.4 W 4 i2.4 W
Creatinineclearance (ml/min/1.73me) Before [ After/"
Serum calcium (mg/dl) Before After7~
M M
0.75 0.75
No No
116.6 • 11.7 113.1 -~: 26.7
111.3 • 0.6 120.1 • 11.0
6.8 -_+ 0.8 7.6 • 0.5
10.0 • 0.5
F F
1.00 0.75
Yes No
89.5 • 9.2 120.0 _+ 1.4
106.7 ___ 8.9 97.5 _+ 17.6
7.0 • 1.0 8.6 • 2.5
9.0 _+ 0.9 9.7 _+ 0.9
9.8 • 0.4
Data represent mean • SEM. *Age given in years and decimals of years according to recommendations of Roche (Growth assessment in abnormal children. Kidney Int 14:369, 1978). tMean • SEM of values collected during treatment. ~Ca X P product, serum calcium x phosphate solubility product during treatment. W e studied two children with congenital hypoparathyroidism and two with pseudohypoparathyroidism, to confirm the data of M a r k o w i t z et al. 12 and to examine further the effects of long-term t r e a t m e n t with 1,25-dihydroxyvit a m i n D3 in the absence of parathyroid action on (1) clinical and biochemical responses, (2) urinary excretions of calcium a n d phosphate, and (3) growth characteristics. Ten normal children aged 11.5 +_ 1.2 years ( m e a n +_ S E M ) served as controls. Fresh morning, fasting "spot" urine specimens and simultaneous blood samples for calcium, phosphate, and creatinine determinations were obtained. CASE REPORTS Patient 1. Idiopathic hypoparathyroidism was diagnosed when this child was 2 months of age after hypocalcemic symptoms prompted studies that confirmed a normal renal tubular response to PTH infusion. The initial serum calcium concentration of 6.8 mg/dl was normalized with administration of vitamin D2 24,000 U/day. However, by 9 years of age, the dose of vitamin D2 had to be increased to 32,000 U/day because of recurrence of hypocalcemia (Fig. 1). One year later, 1,25-dihydroxyvitamin D3 0.5 #g/day Was initiated in place of the vitamin D2. Whereas four episodes of hypocalcemia (<7.5 mg/dl) occurred before 1,25dihydroxyvitamin D~ therapy, no hypocalcemia was noted after initiation of 1,25-dihydroxyvitamin D3. Two episodes of hypercalcemia (to 11.2 mg/dl) occurred in the 72 months of 1,25dihydroxyvitamin-D~ therapy at 0.5 to 0.75 0:g/day. Patient 2. At 6 weeks of age this child had hypocalcemia (6 mg/dl). Hypoparatbyroidism was indicated by renal tubular responsiveness to infusions of parathyroid extract. Hypocalcemic episodes (<7.5 mg/dl) were frequent despite treatment with vitamin D~ at 50,000 to 75,000 U/day. At 9 years of age, vitamin D2 the?apy was replaced by 1,25-dihydroxyvitamin D3, resulting in sustained normalization of serum calcium concentration, except for one transient episode. No hypercalcemia was observed during the 46 months of oral administration of 1,25-dihydroxyvitamin D3 at 0.75 ug/day.
Patient 3. This girl was the product of a normal pregnancy and delivery. She walked at 13 months of age but had slow speech development, recurrent intermittent abdominal pain, thirst, and lethargy. Her round facies, growth retardation, poor dentition, and obesity initially prompted diagnostic study for chronic lymphocytic thyroiditis, adrenal insufficiency, diabetes mellitus, and renal calculi, all of which were ruled out. At age 6 years she had carpopedal spasm and a serum calcium concentration of 7.3 mg/dl; her mental age was 4.5 years. Results of thyroid function studies were again normal; urinary amino acid screen, electroencephalogram, and ophthalmologic examinations yielded normal findings. At age 6.7 years she had a seizure, with serum calcium concentration 6.5 mg/dl and magnesium concentration 1.3 mg/dl. Intravenous administration of 100 U PTE failed to increase urinary calcium or promote phosphaturia, and the diagnosis of pseudohypoparathyroidism was made. Later, the diagnosis of pseudohypoparathyroidism type 2 was made after PTE infusion demonstrated prompt elevation of cAMP excretion. Treatment with vitamin Dz at 50,000 U/day and calcium lactate 10 gin/ m2/day was initiated, and subsequently the dose of vitamin D2 was increased to 125,000 U/day until the child was 14.4 years of age, when 1,25-dihydroxyvitam!n D3 1.00 ug/day replaced the vitamin D2. In the intervening 69 months of treatment with 1,25-dihydroxyvitamin D3, no hypercalcemia was observed. On one occasion, when 1,25-dihydroxyvitamin D3 dosage was reduced to 0.5 ~g/ day, serum calcium concentrations reached 7.1 mg/dl within 1 week. Patient 4. This child had all of the physical markers of pseudohypoparathy~'oidism: short stocky stature, round face, coarse skin, short pudgy fingers, and growth failure of the first, fourth, and fifth metacarpals and first and fifth metatarsals. She was obese and mentally retarded. At age 2 years, serum calcium concentrations were 3.2 to 4.5 mg/dl and phosphate concentration was 8.2 to 9.0 mg/dl. Vitamin D2 dosage was increased from 50,000 U/day to 65,000 U/day, and finally to an average of 125,000 U/day during the first 12.4 years of her life, together with an average calcium lactate supplementation of elemental calcium 600 mg/day. At age 12.4 years, PTE infusion study showed no phosphaturia or elevation in cAMP excretion, thus confirming the clinical impression of pseudohypoparathyroidism type 1.
Volume 106 Number 3
1,25-Dihydroxyvitamin D3 in hypoparathyroidism
VITAMIN Dz
I, 25 OlHYDROXYVITAMINO3
52,000 u/doy 9 ~[~t_.~
1"Smog/day
0,75 mcg/doy p
-'aC~/doy
Serum calcium >11.0 mg/dl
Duration of treatment (too)
Ca x pC product
2
None
72 46
48.9 +_ 6.7 53.5 _+ 5.2
None None
69 68
47.6 _+ 6.9 48.7 _+ 5.8
423
Y
,1/.,
~'0.5 meg/day
SERUM CALCIUM .
.
.
.
SERUM PHOSPHATE
E
....
SERUM ALKALINE PHOSPHATASE
Sustained normalization of the serum calcium concentration was achieved with 1,25-dihydroxyvitaminD 3 at a maintenance dose of 0.75 /~g/day. METHODS All patients (Table) were studied in the Clinical Research Center of the Medical College of Virginia as part of a protocol approved by the Human Research Committee. Informed consent was obtained from both the parents and th e patients. Before admission, the patients had all received maintenance doses of orally administered vitamin D2, which was discontinued on admission. A constant metabolic diet patterned after the previous dietary history was provided, Consisting of 1800 to 2200 calories (25% protein, 35% Carbohydrate, 40% fat). Daily dietary sodium was 60 mEq, sodium chloride supplements 40 mEq, dietary potassium 70 mEq, dietary calcium 600 mg, and phosphorus 1000 mg, based on 1.73 m 2 body surface area. All height measurements were made by a research nurse, with the patient's heels and back in contact with the same stadiometer firmly fixed to the wall. At any determination, the measurements were repeated until three agreed within 0.2 crn.
Aliquots of each well-mixed 24-hour urine collection were analyzed daily for creatinine~3 as an index of completeness of collection and for calcium TM and phosphate.!5 Urinary calcium was determined by atomic absorption spectrophotometry, TM and phosphate by colorimetric spectrophotometry?4 Fasting blood was drawn every 4 days at 7:00 AM, before administration of 1,25dihydroxyvitamin D3, and was analyzed for calcium, ~4 phosphate, TM and alkaline phosphatase. The tubular threshold for phosphate was obtained by plotting the tubular reabsorption of phosphate and serum phosphate concentration on the nomogram developed by Walton and '~BijVoet.~s The patients have been readmitted annually for repeat metabolic balance studies. In addition, during the first year
-- 190~ D 150 .~. 20 ~
--
. . . SERUM . . . . . . . . .U. . . . . . . . . . . . .~. . . . . . . . . SERUM CREATININE
-2
0
2
4
6
YEARS OF TREATMENT Fig. 1. Clinical data in patient 3, with idiopathic hypoparathyroidism.
they were admitted monthly for 2-day studies, under the same protocol for urine, blood, and height measurements. Thereafter, short-term studies have been conducted quarterly. If hypercalcemia (serum calcium >11 mg/dl) was observed at any time, 1,25-dihydroxyvitamin D3 was immediately withheld for 1 week, and restarted at half of its previous dose. After 1 month, the dose was advanced to maintenance dose at 75% of the dose before hypercalcemia. If hypocaleemia (serum calcium concentrations of <7.5 mg/dl on one occasion or <8.0 mg/dl on two occasions within 1 'week) occurred, the dose of 1,25d i h y d r o x y v i t a m i n D 3 was increased by 50% every month until normocalcemia was demonstrated. We aimed to keep the serum calcium concentration between 9.0 and 10.5 mg/dl and the urinary calcium/ creatinine ratio at<0.25. The 1,25-dihydroxyvitamin D3 dosages were originally given once a day, but in the final 2 years of the study, they were administered in split doses. Roentgenograms of the hands and wrists (for bone age) and knees and ankle,s were taken every 6 months for the first 2 years of therapy, and then annually. All data were analyzed for significance~tgy the Student paired t test, ~6 and applied regression analysis by the method of Draper and Smith. ~7
424
Chan et al.
The Journal o f Pediatrics March 1985
+2 SD
5.5
i/ o
o
//
o "3" / "
IO
,
_/
08 %
o
~
o
~
0
2.0
0 O
URINARY CALCIUM
5.0
,,,,7/I
o . / MEAN
oo
oS#o /'fo
E
[]
0.5 0.30
]
URINARY CALCIUM / URINARY CREAT!NINE
~9 I--
MEAN-;"--~
I--
0
B z 0 c)
o
ito
o 9
o
7
o ~
I 0
6 r =0.46 y= 8 . 7 _+ 0.034x I p < 0.001 I n= 88
r = 0.29 y = 8.4 _+O.O05x p < 0.05 t1=47
N 54-
mg/kg/day 0.025
,
0.050
I , I , ,ooo 2 0 0 0
IU/kg/doy V I T A M I N D2
0.075
I
3000
r o
,
z'o
,
go
'
~o
ng/kg/doy I, 2 5 - D I H Y D R O X Y V I T A M I N
D3
Fig. 2. Linear regression relationship between serum calcium concentration and dosage of vitamin D2 and 1,25-dihydroxyvitarain D3. Serum calcium concentrations during treatment represented bY open circles. Serum calcium concentrations at time of presentation (closed circles) not included in statistical analysis.
RESULTS Clinical and biochemical responses. Patient l, with idiopathic hypoparathyroidism, sustained 2 episodes of hypercalcemia (serum calcium concentrations 11.2 and 11.1 mg/dl) during 72 months of treatment with 1,25dihydr0xyvitamin D3. The renal functions were stable, as suggested by mean (_+SEM) creatinine clearance of 111.3 _+ 0.6 ml/min/1.72 m 2 during treatment with 1,25dihydroxyvitamin D3 (Table) and normal serum urea nitrogen and creatinine concentrations for the duration of the study (Fig. ] ) . Hypercalcemia was not encountered in the other patient with idiopathic hypoparathyroidism, nor in the two with pseudohypoparathyr0idism, for up to 69 months (Table). The serum calcium and phosphate products were within the normal range. As estimated by creatinine clearances, deterioration of renal function was not observed. Renal function, as estimated by the reciprocal of serum creatinine concentration,/8-T9 was also stable over the period of study. Patients 2 and 3 each had One episode of hypocalcemia, associated with reciprocal transient increases in serum phosphate concentrations. Hypocalcemia was tim
TUBULAR PHOSPHATE THRESHOLD
YEARS
I I
i 2
I 3
I 4
! 5
O F T R E A T M E N T WITH I 2 5 - D I H Y D R O X Y V I T A M I N D 3
Fig. 3. Mean (_+SD) urinary calcium excretions, urinary calcium/creatinine ratio, and renal tubular threshold for phosphate in control subjects are shown in stippled areas. In comparison, urinary calcium excretion in study patients is higher before, 1,25-dihydroxyvitaminD~ treatment, which may reflect the effect of previous treatment with vitamin D2. Urinary caicium/creatinine ratio is not different between control subjects and patients given 1,25-dihydroxyvitaminD3. Urinary TmP/GFR excretion stays within that of control subjects. Urinary calcium excretion after the fourth year shows higher values.
documented in the other patients and was not symptomatic in patients 2 and 3. Fifty percent increments in the 1,25-dihydroxyvitamin D3 dose were necessary to counter hypocalcemic episodes. Serum calcium concentrations were examined in relation to the corresponding maintenance doses of vitamin D2 and 1,25-dihydroxyvitamin D3, expressed as dose per kilogram body weight per day (Fig. 2). The initial serum calcium concentrations at the time of diagnosis were not included in the regression analysis. The serum concentration of calcium was correlated to the dose of vitamin D2 (r -- 0.29, y = 8.4 + 0.003x, P < 0.05, n, = 47). A positive and significant correlation was established between serum calcium concentrations and the dose of 1,25-dihydroxyvitamin D3 (r = 0.46, y = 8,7 + 0.034x, P < 0.001, n = 88). To achieve sustained control of serum calcium concentrations above 8 mg/dl, the maintenance dose of 1,25dihydroxyvitamin D3 was shown to be between 10 and 40 ng/kg/day. Paired t tests for determining Whether the means are significantly different showed T = 3.27, with 133 degrees of freedom (P = 0.00!). Thus, the two treatments are significantly different with respect to serum calcium concentrations. Urinary calcium and phosphate excretion. The urinary calcium excretion in the untreated state showed concentrations within the range of that in the control subjects and
Volume 106 Number 3
did not change significantly over the 5 years of maintenance 1,25-dihydroxyvitamin D3 therapy (Fig. 3). The urinary calcium excretion when fractionated by urinary creatinine concentrations (Fig. 3) was also within the normal range. The values toward the end of the study were not significantly higher than those during the first 2 years of treatment. The T m P / G F R stayed within normal ranges. Growth characteristics. Except in patient 1 with idiopathic hypoparathyr0idism, who achieved modestly accelerated growth velocity for the first year after initiation of 1,25-dihydroxyvitamin D 3 therapy, but whose maximum growth velocity stayed within that normally expected for chronologic and bone ages, no significant changes in growth were seen. DISCUSSION Our data provide confirmation of the long-term, comprehensive studies of Kooh et al)' and Markowitz et al. ~2It should be emphasized that 1,25-dihydroxyvitamin D3 may be considered "hormonal replacement," because endogenous production of this renal hormone is depressed. To the extent that vitamin D2 is effective, it is postulated that the supraphysiologic concentrations of 25-hydroxyvitamin D have "fooled" the 1,25-dihydroxyvitamin D receptors. In a study concerning vitamin D2 treatment of hypoparathyroidism, Hossain2~reported 29 episodes of hypercalcemia in excess of 11.3 mg/dl in 13 patients. Significant impairment of renal function, with BUN >40 mg/dl and creatinine clearance <50 ml/min during 22 such episodes, and with lasting impairment in five of the 13 patients, prompted the question as to whether vitamin D2 was "a cumulative renal poison."2~The margin of safety between "controlling" and "intoxicating" doses of vitamin D2 or dihydrotachysterol was apparently small. Accordingly, it was suggested that dihydrotachysterol offered no advantage over vitamin D2. However, data by Harrison et al. 2' suggested more rapid reversal of dihydrotachysterol toxicity as compared to that with vitamin D:. Age-specific factors may have accounted for such differences in vitamin D2 toxicity. Kind et al. 22 showed a much lower incidence of hypercalcemia in children with hypoparathyroidism and pseudohypoparathyroidism, at doses of vitamin D2 comparable on a body weight basis to those used by Hossain, 2~assuming normal adult body weights for patients in the latter study. Our data are consistent with those of Harrison et al. 2' and Kind et al. 22 In fact, serum calcium concentrations did not exceed 11 mg/dl on any occasion in our patients receiving vitamin D2 at doses"~of 400 to 3000 I U / k g / d a y (0.012 to 0.075 mg/kg/day). In contrast, during administration of 1,25-dihydroxyvitamin D3, two episodes of serum calcium concentration >11
1,25-Dihydroxyvitamin D3 in hypoparathyroidism
425
mg/dl were observed, but were rapidly reversed with 50% reduction in dosage. After 1 month, advancement to a maintenance dose at 75% of the hypercalccmic dose resulted in no subsequent hypercalcemia for the remaining 5 years of the study. Sustained normalization of serum calcium concentration is clearly observed during treatment with the maintenance dose of 1,25-dihydroxyvitamin D 3 (Fig. 2), but less so with vitamin D2. The lack of correlation between hypercalcemia and the daily dose of vitamin D2 or dihydrotachysterol was initially reported by Hossain. 2~ None of our patients given vitamin D2 or dihydrotachysterol had calcium values of >11 mg/dl, but serum calcium concentrations were >10.5 mg/dl on three occasions, at low maintenance doses of 900, 1700, and 2200 IU/kg/day, respectively (Fig. 2). However, with rare exceptions, the use of 1,25-dihydroxyvitamin D3 was associated with higher serum calcium concentrations. The more frequent serum sampling during the 1,25-dihydroxyvitamin D3 therapy may have contributed to these differences. Moreover, the mean serum calcium concentrations were significantly higher in the period of treatment with 1,25-dihydroxyvitamin D3 compared with that with vitamin D2 (P = 0.001). Such data, together with the more rapid onset and offset of action, provide additional support for the use of 1,25dihydroxyvitamin D3 in hypoparathyroidism and pseudohypoparathyroidism at maintenance dosages of 20 to 40 ng/kg/day. In the diagnosis of hypocalcemia and hypercalcemia, the measurements of ionized calcium23 offer certain advantages over that of total serum calcium24and should be more widely used. We conclude that 1,25-dihydroxyvitamin D 3 will prove to be the therapy of choice in the treatment of idiopathic hypoparathyroidism or pseudohypoparathyroidism because of its effectiveness at a lower maintenance dose, the relative ease with which treatment can be initiated, and the prompt reversibility of toxicity. High doses, however, can result in hypercalcemia and hypercalciuria and therefore require careful follow-up, even with prolonged treatment. We thank Mrs. Marilyn Reilly for secretarial assistance; Martha D. Wellons, B.A., Martha D. Massie, B.A., R.D., and Cecilia Mulroy, B.S., R.D., for research assistance;the entire staff of the Clinical Research Center, especially Margaret A. Carter, R.N., and Burnetl S. Maddox, R.N., for metabolic studies; and Dr. Peter Mamunes for referring two of the patients. REFERENCES
1. Harrison HE, Harrison HC: Disorders of calcium and phosphate metabolism in childhood and adolescence. Philadelphia, 1979, WB Saunders, 208. 2. Root AW, Harrison HH: Recent advances in calcium metab-
426
3. 4. 5.
6.
7.
8.
9.
10.
11.
12.
13.
Chan et al.
olism. II. Disorders of calcium homeostasis. J PEDIATR 88:177, 1976. Ray EW, Gardner LI: Pseudopseudohypoparathyroidismin a child: Report of the youngest case. Pediatrics 23:520, 1959. Cohen ML, Donnell GN: Pseudohypoparathyroidism with hypothyroidism. J PEDIATR 56:369, 1960. DiGeorge AM: Disorders of the parathyroid glands. In Behrman RE, Vaughan VC III, editors: Nelson's textbook of pediatrics. Philadelphia, 1976, WB Saunders. Mawer EB, Backhouse J, Davis M, et al: Metabolic fate of administered 1,25-dihydroxycholecalciferol in controls and in patients with hypoparathyroidism. Lancet 1:1203, 1976. Sinha TS, DeLuca HF, Bell NH: Evidence for a defect in the formation of 1,25-dihydroxyvitamin-D in pseudohypoparathyroidism. Metabolism 26:731, 1977. Werder EA, Kind HP, Egert F, et al: Effective long-term treatment of pseudohypoparathyroidism with oral lahydroxy- and 1,25-dihydroxycholecalciferol. J PEDIATR 89:266, 1976. Balsan S, Garabedian M, Sorgniard R, et al: 1,25-Dihydroxyvitamin D3 and la-hydroxyvitamin D3 in children: Biologic and therapeutic effects in nutritional rickets and different types of vitamin D resistance. Pediatr Res 9:586, 1975. Russell RGG, Smith R, Walton RJ, et al: 1,25-Dihydroxycholecalciferol and la-hydroxycholecalciferol in hypoparathyroidism. Lancet 2:14, 1974. Kooh SW, Fraser D, DeLuca HF, et al: Treatment of hypoparathyroidism and pseudohypoparathyroidism with metabolites of vitamin D: Evidence of impaired conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. N Engl J Med 293:840, 1975. Markowitz ME, Rosen JF, Smith C, et al: t,25-Dihydroxyvitamin D3-treated hypoparathyroidism: 35 patient years in 10 children. J Clin Endocrinol Metab 55:727, 1982. Folin O: On the determination of creatine and creatinine in urine. J Biol Chem 17:469, 1914.
The Journal of Pediatrics March 1985
14. Chart JCM, Kodroff MB, Landwehr DM: Effects of 1,25dihydroxyvitamin D3 on renal function, mineral metabolism and growth in children with severe chronic renal failure. Pediatrics 68:559, 1981. 15. Walton R J, Bijvoet OLM: Nomogram for derivation of renal threshold phosphate concentration. Lancet 2:309, 1975. 16. Colton T: Statistics in medicine. Boston, 1974, Little, Brown & Co, p 382. 17. Draper NR, Smith H: Applied regression analysis, ed 2. New York, 1981, John Wiley & Sons. 18. Chan JCM, Sharpe AR: Glomerular filtration rate in children with advanced chronic renal failure: Methods of determination and clinical applications. Am J Nephrol 2:46, 1982. 19. Mitch WE, Burlington G, Lemann J, et al: A simple method of estimating progression of chronic renal failure. Lancet 2:132, 1976. 20. Hossain M: Vitamin-D intoxication during treatment of hypoparathyroidism. Lancet 1:1149, 1970. 21. Harrison HE, Lifschitz F, Blizzard RM: Comparison between crystalline dihydrotachysterol and calciferol in patients requiring pharmacologic vitamin D therapy. New Engl J Med 276:894, 1967. 22. Kind HP, Handysides A, Kooh SW, et al: Vitamin D therapy in hypoparathyroidism and pseudohypoparathyroidism: Weight-related dosages for initiation of therapy and maintenance therapy. J PEDIATR 91:1006, 1977. 23. Larsson L, Finnstrom O, Nilson B, et al: Evaluation of Radiometer 1CAI as a routine instrument for serum ionized calcium and its application for whole blood capillary samples from newborn infants. Scand J Clin Lab Invest 43(Suppl 165):1, t983. 24. Ladenson JH, Lewis JW, et al: Failure of total calcium corrected for protein, albumin and pH to correctly assess full calcium status. J Clin Endocrinol Metab 46:986, 1978.
James C. M. Chan, M.D., Reuben B. Young, M.D., Michael A. Hartenberg, M.D., and Vernon M. Chinchilli, Ph.D. Richmond,
Virginia
IDIOPATHIC HYPOPARATHYROIDISM ~,2 and pseudohypoparathyroidism3,4 are inherited disorders associated with hypocalcemia, as the result of a congenital deficiency of parathyroid hormone in the former and as a consequence of renal tubular and skeletal resistance to parathyroid hormone in the latter. In hypoparathyroidism the impaired renal hydroxylation of 25-hydroxyvitamin D3 to 1,25From the Departments of Pediatrics, Radiology, and Biostatistics, Medical College o f Virginia; and the Nephrology, GeneticsEndocrine-Metabolism, and Radiology Sections, Children's Medical Center, Virginia Commonwealth University. Supported in part by Grants GCRC R R 0065, R01 A M HD 31370, and R01 A M HD 32431 .from the National Institutes of Health. Submitted for publication June 7, 1984; accepted Aug. 17, 1984. Reprint requests: James C. M. Chan, M.D., Box 498 Medical College of Virginia Station, Richmond, VA 23298.
dihydroxyvitamin D 3 plays an important role in the development of hypocalcemia? ,6 The hypocalcemia of pseudohypoparathyroidism may also be secondary to deficiency of I
cAMP
1,25-dihydroxyvitaminD3 25-hydroxyvitamin D3 TmP/GFR PTH PTE
Cyclic adenosine monophosphate Calcitriol, 1,25-dihydroxycholecalciferol, 1,25-(OH)2-D3, 1,25-D Calcidiol, 25-hydroxych01ecaleiferol, 25-OH-D3 Tubular threshold for phosphate Parathyroid hormone Parathyroid extract
1,25-dihydroxyvitamin D~ associated with parathyroid resistance at the renal tubular sites, 7,8 These observations provide the rationale for the therapeutic use of 1,25dihydroxyvitamin D3 in these disorders. H~
The dournal of P E D I A T R I C S
421
422
Chanet al.
The Journalof Pediatrics March 1985
Table. Clinical a n d biochemical d a t a in four adolescents given 1,25-dihydroxyvitamin D3
Ageatstart e ] Sex I Maintenancetherapy of therapy* 1,25-D supplement Patient[ (yr) ]Rae (~g/day) (Po) Idiopathic hypoparathyroidism 1 10.2 W 2 9.0 W Pseudohypoparathyroidism 3 14.4 W 4 i2.4 W
Creatinineclearance (ml/min/1.73me) Before [ After/"
Serum calcium (mg/dl) Before After7~
M M
0.75 0.75
No No
116.6 • 11.7 113.1 -~: 26.7
111.3 • 0.6 120.1 • 11.0
6.8 -_+ 0.8 7.6 • 0.5
10.0 • 0.5
F F
1.00 0.75
Yes No
89.5 • 9.2 120.0 _+ 1.4
106.7 ___ 8.9 97.5 _+ 17.6
7.0 • 1.0 8.6 • 2.5
9.0 _+ 0.9 9.7 _+ 0.9
9.8 • 0.4
Data represent mean • SEM. *Age given in years and decimals of years according to recommendations of Roche (Growth assessment in abnormal children. Kidney Int 14:369, 1978). tMean • SEM of values collected during treatment. ~Ca X P product, serum calcium x phosphate solubility product during treatment. W e studied two children with congenital hypoparathyroidism and two with pseudohypoparathyroidism, to confirm the data of M a r k o w i t z et al. 12 and to examine further the effects of long-term t r e a t m e n t with 1,25-dihydroxyvit a m i n D3 in the absence of parathyroid action on (1) clinical and biochemical responses, (2) urinary excretions of calcium a n d phosphate, and (3) growth characteristics. Ten normal children aged 11.5 +_ 1.2 years ( m e a n +_ S E M ) served as controls. Fresh morning, fasting "spot" urine specimens and simultaneous blood samples for calcium, phosphate, and creatinine determinations were obtained. CASE REPORTS Patient 1. Idiopathic hypoparathyroidism was diagnosed when this child was 2 months of age after hypocalcemic symptoms prompted studies that confirmed a normal renal tubular response to PTH infusion. The initial serum calcium concentration of 6.8 mg/dl was normalized with administration of vitamin D2 24,000 U/day. However, by 9 years of age, the dose of vitamin D2 had to be increased to 32,000 U/day because of recurrence of hypocalcemia (Fig. 1). One year later, 1,25-dihydroxyvitamin D3 0.5 #g/day Was initiated in place of the vitamin D2. Whereas four episodes of hypocalcemia (<7.5 mg/dl) occurred before 1,25dihydroxyvitamin D~ therapy, no hypocalcemia was noted after initiation of 1,25-dihydroxyvitamin D3. Two episodes of hypercalcemia (to 11.2 mg/dl) occurred in the 72 months of 1,25dihydroxyvitamin-D~ therapy at 0.5 to 0.75 0:g/day. Patient 2. At 6 weeks of age this child had hypocalcemia (6 mg/dl). Hypoparatbyroidism was indicated by renal tubular responsiveness to infusions of parathyroid extract. Hypocalcemic episodes (<7.5 mg/dl) were frequent despite treatment with vitamin D~ at 50,000 to 75,000 U/day. At 9 years of age, vitamin D2 the?apy was replaced by 1,25-dihydroxyvitamin D3, resulting in sustained normalization of serum calcium concentration, except for one transient episode. No hypercalcemia was observed during the 46 months of oral administration of 1,25-dihydroxyvitamin D3 at 0.75 ug/day.
Patient 3. This girl was the product of a normal pregnancy and delivery. She walked at 13 months of age but had slow speech development, recurrent intermittent abdominal pain, thirst, and lethargy. Her round facies, growth retardation, poor dentition, and obesity initially prompted diagnostic study for chronic lymphocytic thyroiditis, adrenal insufficiency, diabetes mellitus, and renal calculi, all of which were ruled out. At age 6 years she had carpopedal spasm and a serum calcium concentration of 7.3 mg/dl; her mental age was 4.5 years. Results of thyroid function studies were again normal; urinary amino acid screen, electroencephalogram, and ophthalmologic examinations yielded normal findings. At age 6.7 years she had a seizure, with serum calcium concentration 6.5 mg/dl and magnesium concentration 1.3 mg/dl. Intravenous administration of 100 U PTE failed to increase urinary calcium or promote phosphaturia, and the diagnosis of pseudohypoparathyroidism was made. Later, the diagnosis of pseudohypoparathyroidism type 2 was made after PTE infusion demonstrated prompt elevation of cAMP excretion. Treatment with vitamin Dz at 50,000 U/day and calcium lactate 10 gin/ m2/day was initiated, and subsequently the dose of vitamin D2 was increased to 125,000 U/day until the child was 14.4 years of age, when 1,25-dihydroxyvitam!n D3 1.00 ug/day replaced the vitamin D2. In the intervening 69 months of treatment with 1,25-dihydroxyvitamin D3, no hypercalcemia was observed. On one occasion, when 1,25-dihydroxyvitamin D3 dosage was reduced to 0.5 ~g/ day, serum calcium concentrations reached 7.1 mg/dl within 1 week. Patient 4. This child had all of the physical markers of pseudohypoparathy~'oidism: short stocky stature, round face, coarse skin, short pudgy fingers, and growth failure of the first, fourth, and fifth metacarpals and first and fifth metatarsals. She was obese and mentally retarded. At age 2 years, serum calcium concentrations were 3.2 to 4.5 mg/dl and phosphate concentration was 8.2 to 9.0 mg/dl. Vitamin D2 dosage was increased from 50,000 U/day to 65,000 U/day, and finally to an average of 125,000 U/day during the first 12.4 years of her life, together with an average calcium lactate supplementation of elemental calcium 600 mg/day. At age 12.4 years, PTE infusion study showed no phosphaturia or elevation in cAMP excretion, thus confirming the clinical impression of pseudohypoparathyroidism type 1.
Volume 106 Number 3
1,25-Dihydroxyvitamin D3 in hypoparathyroidism
VITAMIN Dz
I, 25 OlHYDROXYVITAMINO3
52,000 u/doy 9 ~[~t_.~
1"Smog/day
0,75 mcg/doy p
-'aC~/doy
Serum calcium >11.0 mg/dl
Duration of treatment (too)
Ca x pC product
2
None
72 46
48.9 +_ 6.7 53.5 _+ 5.2
None None
69 68
47.6 _+ 6.9 48.7 _+ 5.8
423
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~'0.5 meg/day
SERUM CALCIUM .
.
.
.
SERUM PHOSPHATE
E
....
SERUM ALKALINE PHOSPHATASE
Sustained normalization of the serum calcium concentration was achieved with 1,25-dihydroxyvitaminD 3 at a maintenance dose of 0.75 /~g/day. METHODS All patients (Table) were studied in the Clinical Research Center of the Medical College of Virginia as part of a protocol approved by the Human Research Committee. Informed consent was obtained from both the parents and th e patients. Before admission, the patients had all received maintenance doses of orally administered vitamin D2, which was discontinued on admission. A constant metabolic diet patterned after the previous dietary history was provided, Consisting of 1800 to 2200 calories (25% protein, 35% Carbohydrate, 40% fat). Daily dietary sodium was 60 mEq, sodium chloride supplements 40 mEq, dietary potassium 70 mEq, dietary calcium 600 mg, and phosphorus 1000 mg, based on 1.73 m 2 body surface area. All height measurements were made by a research nurse, with the patient's heels and back in contact with the same stadiometer firmly fixed to the wall. At any determination, the measurements were repeated until three agreed within 0.2 crn.
Aliquots of each well-mixed 24-hour urine collection were analyzed daily for creatinine~3 as an index of completeness of collection and for calcium TM and phosphate.!5 Urinary calcium was determined by atomic absorption spectrophotometry, TM and phosphate by colorimetric spectrophotometry?4 Fasting blood was drawn every 4 days at 7:00 AM, before administration of 1,25dihydroxyvitamin D3, and was analyzed for calcium, ~4 phosphate, TM and alkaline phosphatase. The tubular threshold for phosphate was obtained by plotting the tubular reabsorption of phosphate and serum phosphate concentration on the nomogram developed by Walton and '~BijVoet.~s The patients have been readmitted annually for repeat metabolic balance studies. In addition, during the first year
-- 190~ D 150 .~. 20 ~
--
. . . SERUM . . . . . . . . .U. . . . . . . . . . . . .~. . . . . . . . . SERUM CREATININE
-2
0
2
4
6
YEARS OF TREATMENT Fig. 1. Clinical data in patient 3, with idiopathic hypoparathyroidism.
they were admitted monthly for 2-day studies, under the same protocol for urine, blood, and height measurements. Thereafter, short-term studies have been conducted quarterly. If hypercalcemia (serum calcium >11 mg/dl) was observed at any time, 1,25-dihydroxyvitamin D3 was immediately withheld for 1 week, and restarted at half of its previous dose. After 1 month, the dose was advanced to maintenance dose at 75% of the dose before hypercalcemia. If hypocaleemia (serum calcium concentrations of <7.5 mg/dl on one occasion or <8.0 mg/dl on two occasions within 1 'week) occurred, the dose of 1,25d i h y d r o x y v i t a m i n D 3 was increased by 50% every month until normocalcemia was demonstrated. We aimed to keep the serum calcium concentration between 9.0 and 10.5 mg/dl and the urinary calcium/ creatinine ratio at<0.25. The 1,25-dihydroxyvitamin D3 dosages were originally given once a day, but in the final 2 years of the study, they were administered in split doses. Roentgenograms of the hands and wrists (for bone age) and knees and ankle,s were taken every 6 months for the first 2 years of therapy, and then annually. All data were analyzed for significance~tgy the Student paired t test, ~6 and applied regression analysis by the method of Draper and Smith. ~7
424
Chan et al.
The Journal o f Pediatrics March 1985
+2 SD
5.5
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o
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o "3" / "
IO
,
_/
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o
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URINARY CALCIUM
5.0
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oo
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URINARY CALCIUM / URINARY CREAT!NINE
~9 I--
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o
ito
o 9
o
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6 r =0.46 y= 8 . 7 _+ 0.034x I p < 0.001 I n= 88
r = 0.29 y = 8.4 _+O.O05x p < 0.05 t1=47
N 54-
mg/kg/day 0.025
,
0.050
I , I , ,ooo 2 0 0 0
IU/kg/doy V I T A M I N D2
0.075
I
3000
r o
,
z'o
,
go
'
~o
ng/kg/doy I, 2 5 - D I H Y D R O X Y V I T A M I N
D3
Fig. 2. Linear regression relationship between serum calcium concentration and dosage of vitamin D2 and 1,25-dihydroxyvitarain D3. Serum calcium concentrations during treatment represented bY open circles. Serum calcium concentrations at time of presentation (closed circles) not included in statistical analysis.
RESULTS Clinical and biochemical responses. Patient l, with idiopathic hypoparathyroidism, sustained 2 episodes of hypercalcemia (serum calcium concentrations 11.2 and 11.1 mg/dl) during 72 months of treatment with 1,25dihydr0xyvitamin D3. The renal functions were stable, as suggested by mean (_+SEM) creatinine clearance of 111.3 _+ 0.6 ml/min/1.72 m 2 during treatment with 1,25dihydroxyvitamin D3 (Table) and normal serum urea nitrogen and creatinine concentrations for the duration of the study (Fig. ] ) . Hypercalcemia was not encountered in the other patient with idiopathic hypoparathyroidism, nor in the two with pseudohypoparathyr0idism, for up to 69 months (Table). The serum calcium and phosphate products were within the normal range. As estimated by creatinine clearances, deterioration of renal function was not observed. Renal function, as estimated by the reciprocal of serum creatinine concentration,/8-T9 was also stable over the period of study. Patients 2 and 3 each had One episode of hypocalcemia, associated with reciprocal transient increases in serum phosphate concentrations. Hypocalcemia was tim
TUBULAR PHOSPHATE THRESHOLD
YEARS
I I
i 2
I 3
I 4
! 5
O F T R E A T M E N T WITH I 2 5 - D I H Y D R O X Y V I T A M I N D 3
Fig. 3. Mean (_+SD) urinary calcium excretions, urinary calcium/creatinine ratio, and renal tubular threshold for phosphate in control subjects are shown in stippled areas. In comparison, urinary calcium excretion in study patients is higher before, 1,25-dihydroxyvitaminD~ treatment, which may reflect the effect of previous treatment with vitamin D2. Urinary caicium/creatinine ratio is not different between control subjects and patients given 1,25-dihydroxyvitaminD3. Urinary TmP/GFR excretion stays within that of control subjects. Urinary calcium excretion after the fourth year shows higher values.
documented in the other patients and was not symptomatic in patients 2 and 3. Fifty percent increments in the 1,25-dihydroxyvitamin D3 dose were necessary to counter hypocalcemic episodes. Serum calcium concentrations were examined in relation to the corresponding maintenance doses of vitamin D2 and 1,25-dihydroxyvitamin D3, expressed as dose per kilogram body weight per day (Fig. 2). The initial serum calcium concentrations at the time of diagnosis were not included in the regression analysis. The serum concentration of calcium was correlated to the dose of vitamin D2 (r -- 0.29, y = 8.4 + 0.003x, P < 0.05, n, = 47). A positive and significant correlation was established between serum calcium concentrations and the dose of 1,25-dihydroxyvitamin D3 (r = 0.46, y = 8,7 + 0.034x, P < 0.001, n = 88). To achieve sustained control of serum calcium concentrations above 8 mg/dl, the maintenance dose of 1,25dihydroxyvitamin D3 was shown to be between 10 and 40 ng/kg/day. Paired t tests for determining Whether the means are significantly different showed T = 3.27, with 133 degrees of freedom (P = 0.00!). Thus, the two treatments are significantly different with respect to serum calcium concentrations. Urinary calcium and phosphate excretion. The urinary calcium excretion in the untreated state showed concentrations within the range of that in the control subjects and
Volume 106 Number 3
did not change significantly over the 5 years of maintenance 1,25-dihydroxyvitamin D3 therapy (Fig. 3). The urinary calcium excretion when fractionated by urinary creatinine concentrations (Fig. 3) was also within the normal range. The values toward the end of the study were not significantly higher than those during the first 2 years of treatment. The T m P / G F R stayed within normal ranges. Growth characteristics. Except in patient 1 with idiopathic hypoparathyr0idism, who achieved modestly accelerated growth velocity for the first year after initiation of 1,25-dihydroxyvitamin D 3 therapy, but whose maximum growth velocity stayed within that normally expected for chronologic and bone ages, no significant changes in growth were seen. DISCUSSION Our data provide confirmation of the long-term, comprehensive studies of Kooh et al)' and Markowitz et al. ~2It should be emphasized that 1,25-dihydroxyvitamin D3 may be considered "hormonal replacement," because endogenous production of this renal hormone is depressed. To the extent that vitamin D2 is effective, it is postulated that the supraphysiologic concentrations of 25-hydroxyvitamin D have "fooled" the 1,25-dihydroxyvitamin D receptors. In a study concerning vitamin D2 treatment of hypoparathyroidism, Hossain2~reported 29 episodes of hypercalcemia in excess of 11.3 mg/dl in 13 patients. Significant impairment of renal function, with BUN >40 mg/dl and creatinine clearance <50 ml/min during 22 such episodes, and with lasting impairment in five of the 13 patients, prompted the question as to whether vitamin D2 was "a cumulative renal poison."2~The margin of safety between "controlling" and "intoxicating" doses of vitamin D2 or dihydrotachysterol was apparently small. Accordingly, it was suggested that dihydrotachysterol offered no advantage over vitamin D2. However, data by Harrison et al. 2' suggested more rapid reversal of dihydrotachysterol toxicity as compared to that with vitamin D:. Age-specific factors may have accounted for such differences in vitamin D2 toxicity. Kind et al. 22 showed a much lower incidence of hypercalcemia in children with hypoparathyroidism and pseudohypoparathyroidism, at doses of vitamin D2 comparable on a body weight basis to those used by Hossain, 2~assuming normal adult body weights for patients in the latter study. Our data are consistent with those of Harrison et al. 2' and Kind et al. 22 In fact, serum calcium concentrations did not exceed 11 mg/dl on any occasion in our patients receiving vitamin D2 at doses"~of 400 to 3000 I U / k g / d a y (0.012 to 0.075 mg/kg/day). In contrast, during administration of 1,25-dihydroxyvitamin D3, two episodes of serum calcium concentration >11
1,25-Dihydroxyvitamin D3 in hypoparathyroidism
425
mg/dl were observed, but were rapidly reversed with 50% reduction in dosage. After 1 month, advancement to a maintenance dose at 75% of the hypercalccmic dose resulted in no subsequent hypercalcemia for the remaining 5 years of the study. Sustained normalization of serum calcium concentration is clearly observed during treatment with the maintenance dose of 1,25-dihydroxyvitamin D 3 (Fig. 2), but less so with vitamin D2. The lack of correlation between hypercalcemia and the daily dose of vitamin D2 or dihydrotachysterol was initially reported by Hossain. 2~ None of our patients given vitamin D2 or dihydrotachysterol had calcium values of >11 mg/dl, but serum calcium concentrations were >10.5 mg/dl on three occasions, at low maintenance doses of 900, 1700, and 2200 IU/kg/day, respectively (Fig. 2). However, with rare exceptions, the use of 1,25-dihydroxyvitamin D3 was associated with higher serum calcium concentrations. The more frequent serum sampling during the 1,25-dihydroxyvitamin D3 therapy may have contributed to these differences. Moreover, the mean serum calcium concentrations were significantly higher in the period of treatment with 1,25-dihydroxyvitamin D3 compared with that with vitamin D2 (P = 0.001). Such data, together with the more rapid onset and offset of action, provide additional support for the use of 1,25dihydroxyvitamin D3 in hypoparathyroidism and pseudohypoparathyroidism at maintenance dosages of 20 to 40 ng/kg/day. In the diagnosis of hypocalcemia and hypercalcemia, the measurements of ionized calcium23 offer certain advantages over that of total serum calcium24and should be more widely used. We conclude that 1,25-dihydroxyvitamin D 3 will prove to be the therapy of choice in the treatment of idiopathic hypoparathyroidism or pseudohypoparathyroidism because of its effectiveness at a lower maintenance dose, the relative ease with which treatment can be initiated, and the prompt reversibility of toxicity. High doses, however, can result in hypercalcemia and hypercalciuria and therefore require careful follow-up, even with prolonged treatment. We thank Mrs. Marilyn Reilly for secretarial assistance; Martha D. Wellons, B.A., Martha D. Massie, B.A., R.D., and Cecilia Mulroy, B.S., R.D., for research assistance;the entire staff of the Clinical Research Center, especially Margaret A. Carter, R.N., and Burnetl S. Maddox, R.N., for metabolic studies; and Dr. Peter Mamunes for referring two of the patients. REFERENCES
1. Harrison HE, Harrison HC: Disorders of calcium and phosphate metabolism in childhood and adolescence. Philadelphia, 1979, WB Saunders, 208. 2. Root AW, Harrison HH: Recent advances in calcium metab-
426
3. 4. 5.
6.
7.
8.
9.
10.
11.
12.
13.
Chan et al.
olism. II. Disorders of calcium homeostasis. J PEDIATR 88:177, 1976. Ray EW, Gardner LI: Pseudopseudohypoparathyroidismin a child: Report of the youngest case. Pediatrics 23:520, 1959. Cohen ML, Donnell GN: Pseudohypoparathyroidism with hypothyroidism. J PEDIATR 56:369, 1960. DiGeorge AM: Disorders of the parathyroid glands. In Behrman RE, Vaughan VC III, editors: Nelson's textbook of pediatrics. Philadelphia, 1976, WB Saunders. Mawer EB, Backhouse J, Davis M, et al: Metabolic fate of administered 1,25-dihydroxycholecalciferol in controls and in patients with hypoparathyroidism. Lancet 1:1203, 1976. Sinha TS, DeLuca HF, Bell NH: Evidence for a defect in the formation of 1,25-dihydroxyvitamin-D in pseudohypoparathyroidism. Metabolism 26:731, 1977. Werder EA, Kind HP, Egert F, et al: Effective long-term treatment of pseudohypoparathyroidism with oral lahydroxy- and 1,25-dihydroxycholecalciferol. J PEDIATR 89:266, 1976. Balsan S, Garabedian M, Sorgniard R, et al: 1,25-Dihydroxyvitamin D3 and la-hydroxyvitamin D3 in children: Biologic and therapeutic effects in nutritional rickets and different types of vitamin D resistance. Pediatr Res 9:586, 1975. Russell RGG, Smith R, Walton RJ, et al: 1,25-Dihydroxycholecalciferol and la-hydroxycholecalciferol in hypoparathyroidism. Lancet 2:14, 1974. Kooh SW, Fraser D, DeLuca HF, et al: Treatment of hypoparathyroidism and pseudohypoparathyroidism with metabolites of vitamin D: Evidence of impaired conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. N Engl J Med 293:840, 1975. Markowitz ME, Rosen JF, Smith C, et al: t,25-Dihydroxyvitamin D3-treated hypoparathyroidism: 35 patient years in 10 children. J Clin Endocrinol Metab 55:727, 1982. Folin O: On the determination of creatine and creatinine in urine. J Biol Chem 17:469, 1914.
The Journal of Pediatrics March 1985
14. Chart JCM, Kodroff MB, Landwehr DM: Effects of 1,25dihydroxyvitamin D3 on renal function, mineral metabolism and growth in children with severe chronic renal failure. Pediatrics 68:559, 1981. 15. Walton R J, Bijvoet OLM: Nomogram for derivation of renal threshold phosphate concentration. Lancet 2:309, 1975. 16. Colton T: Statistics in medicine. Boston, 1974, Little, Brown & Co, p 382. 17. Draper NR, Smith H: Applied regression analysis, ed 2. New York, 1981, John Wiley & Sons. 18. Chan JCM, Sharpe AR: Glomerular filtration rate in children with advanced chronic renal failure: Methods of determination and clinical applications. Am J Nephrol 2:46, 1982. 19. Mitch WE, Burlington G, Lemann J, et al: A simple method of estimating progression of chronic renal failure. Lancet 2:132, 1976. 20. Hossain M: Vitamin-D intoxication during treatment of hypoparathyroidism. Lancet 1:1149, 1970. 21. Harrison HE, Lifschitz F, Blizzard RM: Comparison between crystalline dihydrotachysterol and calciferol in patients requiring pharmacologic vitamin D therapy. New Engl J Med 276:894, 1967. 22. Kind HP, Handysides A, Kooh SW, et al: Vitamin D therapy in hypoparathyroidism and pseudohypoparathyroidism: Weight-related dosages for initiation of therapy and maintenance therapy. J PEDIATR 91:1006, 1977. 23. Larsson L, Finnstrom O, Nilson B, et al: Evaluation of Radiometer 1CAI as a routine instrument for serum ionized calcium and its application for whole blood capillary samples from newborn infants. Scand J Clin Lab Invest 43(Suppl 165):1, t983. 24. Ladenson JH, Lewis JW, et al: Failure of total calcium corrected for protein, albumin and pH to correctly assess full calcium status. J Clin Endocrinol Metab 46:986, 1978.