Pseudohypoparathyroidism

Pseudohypoparathyroidism Disappearance

of the Resistance to Parathyroid Extract During

Treatment with Vitamin D

WALTER STaGMANN,

M.D.

Graz, Austria JAN A. FISCHER, M.D. Zurich, Switzerland

From the Department of Pediatrics, University of Graz, Graz, Austria; and the Research Laboratory for Calcium Metabolism, Departments of Orthopedic Surgery and Medicine, University of Zurich, Zurich, Switzerland. This work was supported by the Schweizerische Verein Balgrist. Requests for reprints should be addressed to Dr. Jan A. Fischer, Orthopadische Universitiitsklinik Balgrist, Forchstrasse 340, 8008 Zurich, Switzerland. Manuscript accepted June 12, 1974. 149

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Serum immunoreactive parathyroid hormone (IPTH) levels were increased in a 15 year old girl with pseudohypoparathyroidism, hypocalcemia, hyperphosphatemia, and minlmal phosphaturic and absent hypercalcemic responses to exogenous parathyroid extract (PTE). Following normalization of the serum calcium concentration with vitamin D, serum IPTH and phosphate concentrations returned to the normal range, and phosphaturia could be clearly stimulated and hypercalcemia induced by PTE. On the other hand, the urinary cyclic adenosine 3’,5’-monophosphate (cyclic AMP) excretion could not be stimulated, suggesting that in this case, there appears to be no relationship between the urinary excretion of cyclic AMP and the phosphaturic effect of PTE. The minimal phosphaturic effect and the lack of hypercalcemic effects of PTE in untreated pseudohypoparathyroidism can be explained by the secondary hyperparathyrotdism causing elevated iPTH levels rather than by a defect at the level of the receptor sites. A requirement of pharmacologic amounts of vitamin D per se, however, for the responsiveness of patients wlth pseudohypoparathyroidism to PTE cannot be ruled out. Albright et al. [l] demonstrated that pseudohypoparathyroidism is not caused by a lack of parathyroid hormone (PTH) but by an inability to respond to it. The finding that the mechanism of action of PTH is apparently mediated through an activation of adenylate cyclase and that the urinary excretion of cyclic adenosine 3’,5’-monophosphate (cyclic AMP) cannot be stimulated with parathyroid hormone in pseudohypoparathyroidism gave support to the hypothesis that the metabolic defect of the disorder could be caused by a lack or defective forms of PTH-sensitive receptors in bone and kidney [2]. In some patients with pseudohypoparathyroidism, there is histologic evidence of osteitis fibrosa [ 3-51. Some patients show a partial resistance only to exogenous parathyroid extract (PTE) [ 1,3-g] ; recent studies gave evidence that the responsiveness to PTE improved after treatment with vitamin D [7,8]. lmmunoreactive PTH (iPTH) was demonstrated in peripheral serums of patients with pseudohypoparathyroidism [2,4,5,10-131. In view of the known resistance of patients with primary hyperparathyroidism to exogenous PTE [ 141 and the inverse relation between serum iPTH and calcium levels [ 15,161, we have studied the responsiveness of the PTH-sensitive receptor sites to PTE in a patient with pseudohypoparathyroidism before and during normalization of the serum calcium and iPTH levels with vitamin D.

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Figure I. Metabolic data on a patient with pseudohypoparathyroidism show the effect of treatment with vitamin D on . , serum calcium, phosphorus and iPTH levels. Ordfnafe: serum calcium, phosphorus and iPTH concentrations (the crosshatched area indicates the normal range), as well as the amount of vitamin & administered per day. Abscissa: time in months and years. CASE REPORT The mother of the patient suffers from pseudopseudohypoparathyroidism with short stature and soft tissue calcifications and a normal serum iPTH concentration (28 nglml) (normal range: undetectable to 40 ng/ml) [ 171. The diagnosis of pseudohypoparathyroidism was made in the 15 year old girl on the basis of untreated tetanic cramps since the age of 4 years and the characteristic physical signs (obesity, round face, short stature, cataracts, mental retardation and dental defects). Roentgenographic examinations revealed ectopic subcutaneous and basal ganglia calcifications, as well as brachydactyly. Laboratory results included decreased serum calcium (6.1 and 5.5 mg/lOO ml) and increased iPTH (64 and 77 ng/ml) levels, the serum inorganic phosphorus was increased (7.7 and 8.6 mg/iOO ml), the phosphate clearance was 2.8 ml/min/ 1.73 m* and the tubular reabsorption of phosphate 98 per cent (Figure 1). There were no symptoms of steatorrhea or renal disease. The fecal fat excretion (7.9 g/3 day collection period), xylose resorption (18.7 and 23.1 per cent/4 hours), and the creatinine clearance (113 ml/ minI1.73 m*) were normal. The serum alkaline phosphatase (40 mU/ml), magnesium (1.9 mg/lOO ml) and thyroxine (3.6 pg/lOO ml) levels were within the normal range. The patient was subsequently treated with vitamin 0s (1

to 5 mg/day orally) (Figure l), and the serum calcium, iPTH and phosphorus levels returned into the normal range. There was an increase of the phosphate clearance from 2.8 to 6.2 and 11.8 ml/min/1.73 m* with a concomitant decrease of the tubular reabsorption of phosphate from 98 to 95 and 87 per cent. METHODS Calcium was determined by emission flame spectrophotometry, phosphate by the method of Fiske and Subbarow [ 181, and creatinine according to Folin and Wu [ 191; serum iPTH was estimated in peripheral serums according to Arnaud, Tsao and Littledike [ 161 with the only modification that a crude human tissue culture standard (C-72) was used. Dilution curves of the tissue culture standard and hyperparathyroid serums, using antiporcine PTH obtained in a guinea pig (GPIM), showed superimposition indicating immunologic similarity [ 201. Normal iPTH levels (in 42 control subjects with normal serum calcium [total and ionized], phosphorus, alkaline phosphatase and creatinine) ranged from undetectable to 40 ng/ml [ 171. All the iPTH concentrations were determined in a single assay (coefficient of variation 12 per cent). Urinary cyclic AMP was determined by Dr. G. van den Berghe, University of Louvain, Belgium [21]. July 1975

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200 US&J P;‘E iv 2

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Urinary phosphorus and cyclic AMP excretion in a patient with pseudohypoparathyroidism in response to PTE injected before and during treatment with vitamin 4. A, before treatment with vitamin 4. B, during treatment with vitamin L?J (4 mg/day orally). a = 1st control day. b = 2nd experimental day when 200 USP units of PTE were injected intravenously at 2 PM.

Figure 2.

L1,2,3,4,5861 a

123456 b

RESULTS OF SPECIAL STUDIES Effects of Exogenous PTE. The effects of a single batch of parathyroid extract (Lilly) on the urinary phosphorous excretion and on the serum calcium levels were studied before (serum calcium 6.1 mg/ 100 ml, iPTH 64 ng/ml) and during treatment with vitamin D for 10 months (serum calcium 9.8 mg/lOO ml, iPTH 14 ng/ml). At this time, the effect of PTE on urinary cyclic AMP was also studied. Urinary Phosphate and Cyclic AMP Excretion (Figure 2). Urine was collected at 1 hour time intervals from 12 AM to 6 PM during a 1st control day and a 2nd experimental day, when 200 USP units of PTE (Lilly) were injected intravenously within 10 to 20 seconds at 2 PM [ 221. The per cent change of the urinary phosphorus excretion (mg/min) between the 2nd and the 1st day from 2 to 6 PM was calculated.

Before treatment with vitamin D, the per cent increase of the urinary phosphorus excretion amounted to 72 per cent: this contrasted with a prompt and dramatic increase of 363 per cent during treatment with vitamin D. The urinary cyclic AMP and creatinine excretions were only determined during treatment with vitamin D and remained unchanged. Serum collected at 4 PM was analyzed for phosphate and creatinine. The tubular reabsorption of phosphate decreased from 86.5 to 6 1.7 per cent between 2 and 6 PM. Serum Calcium (Figure 3). Injections of 700 USP units of PTE/day were given at 8 hour intervals until a continuous rise of the serum calcium concentration could be observed, but not for longer than 7 days. Before treatment with vitamin D, PTE had no consistent effect on the serum calcium concentration: dur-

Figure 3. Serum calcium levels in a patient with pseudohypoparathyrotiism in response to PTE injected before and during treatment with vitamin &. A, before treatment with vitamin 5. B, during treatment with vitamin 4 (4 mg/day orally). The arrows indicate intramuscular injections of 233 USP units of PTE at 8 hour intervals. 142

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ing treatment with vitamin D, the serum calcium was increased from 9.5 to ‘14.4 mg/lOO ml on the 4th treatment day. Serum iPTH Before and After Calcium Infusion. The serum calcium was increased from 8.9 to 14.1 mg/lOO ml following an intravenous infusion of calcium (15 mg/kg/body weight) as calcium gluconate between 9 and 12 PM, and iPTH levels were lowered from 32 to 12 ng/ml.

The diagnosis of pseudohypoparathyroidism was established on the basis of the typical physical signs, the lowered serum calcium and increased serum iPTH and phosphorus levels, and the resistance of urinary cyclic AMP excretion to PTE [l-13]. Following treatment with vitamin D, the serum calcium, phosphorous and iPTH levels were normalized, and the patient became clearly responsive to exogenous PTE with an increase in urinary phosphate excretion and in serum calcium concentration. This is in line with previous reports demonstrating that vitamin D improved the responsiveness of patients with pseudohypoparathyroidism to parathyroid hormone [7,8]. Vitamin D, in relatively large amounts, was required for the normalization of the serum calcium, phosphorus and iPTH levels in our patient. The amounts, however, were comparable to the dose of vitamin D occasionally used for the treatment of true hypoparathyroidism [23]. Since patients with true hypoparathyroidism clearly respond to PTE with an increase in urinary phosphate excretion and in serum calcium concentration prior to treatment with vitamin D [8], the hypocalcemia and the hyperphosphatemia appear unimportant in this respect. It remains to be shown whether vitamin D in pharmacologic amounts per se restores the responsiveness to PTE in patients with pseudohypoparathyroidism. The urinary cyclic AMP excretion was not affected after an intravenous injection of PTE, even when the kidney tubules clearly responded with an increased urinary phosphorus excretion and a concomitant lowering of the tubular reabsorption of phosphate [3,5,8,9]. Marcus et al. [24] demonstrated normal adenylate cyclase activity in vitro in the renal cortex of a patient with pseudohypoparathyroidism. A defect in the transport of cyclic AMP across the tubular membranes or increased metabolic degradation could possibly explain the absent urinary cyclic AMP response to PTE. On the other hand, stimulation of a tubular adenylate cyclase may not be essential for the biologic responsiveness of the renal receptor sites to PTH in pseudohypoparathyroidism type I [ 131. The relevance of this finding cannot be judged under in vivo conditions. In pseudohypoparathyroidism type II with a normal urinary cyclic AMP re-

FISCHER

sponse, but absent responses of the urinary phosphate excretion and serum calcium to PTH, the defect appears to represent a failure of intracellular receptors of cyclic AMP [ 131. In view of the suppressibility of the iPTH levels with a calcium infusion in our patient and the negative relationship between serum calcium and iPTH levels, it appears that a normal secretory activity of the parathyroid glands was present [ 161. The possibility remains that exogenous PTE is ineffective in our patient as long as the endogenous iPTH levels are raised. It can be speculated than an immunoreactive, but biologically inactive PTH occupies the receptor sites [ 12,251. The resistance observed to exogenous PTE is in line with Becker et al. [ 141, who showed a smaller decrease in tubular reabsorption of phosphate after infusions with PTE in patients with primary hyperparathyroidism and presumably increased levels of biologically active PTH than in normal subjects. Removal of the parathyroid tumors in patients with primary hyperparathyroidism or the normalization of elevated iPTH levels with vitamin D in our patient led to the disappearance of the so-called resistance of the biologic receptor sites to exogenous PTE; the responsiveness is probably dependent in part, in our case at least, on the amount of endogenous parathyroid hormone present.

ACKNOWLEDGMENT We are indebted to Dr. G. van den Berghe, University of Louvain, Belgium, for the urinary cyclic AMP determinations: to Dr. C. D. Arnaud, Mayo Clinic, Rochester, Minn. for the generous gift of the antiserum and tissue culture standard: and to Bayer Pharma, Zurich, Switzerland, for the Trasylol used in the radioimmunoassay for PTH. ADDENDUM After submission of our manuscript, Rodriguez et al. [26] presented comparable results in a case of pseudohypoparathyroidism type II. The patient became responsive to exogenous PTE during treatment with calcium infusions, which thus restored the responsiveness to PTE in the absence of a treatment with vitamin D. The authors claim, furthermore, that the infusions of calcium lead to a normal responsiveness PTE of the renal tubules despite an increased iPTH level. Since calcium infusions may normalize iPTH levels, as the authors have demonstrated with a prolonged calcium infusion, and since the concentration of certain iPTH fragments may remain elevated for several hours [27,28], the conclusion that calcium infusions alone are the reason for the normalization of the PTE response appears not to be warranted. July 1975

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