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Evaluation of renal parathyroid hormone receptor function in myotonic dystrophy
Journal of the Neurological Sciences, 1985, 70:339-346 Elsevier JNS 2556
Evaluation of Renal Parathyroid Hormone Recept Function in Myotonic Dystrophy Yoko Konagaya, Masaaki Konagaya, Yukio Mano, Tetsuya Takayanagi Akio Tomita t Department of Neurology, Nara Medical University, and 1First Department of Internal Medicine, Na University School of Medicine, Nagoya (Japan) (Received 6 December, 1984) (Revised, received 4 June, 1985) (Accepted 7 June, 1985)
SUMMARY
Endocrine abnormalities in myotonic dystrophy (MyD) reflect some of the m systemic involvement resulting from this disorder. One of these, abnormal ins secretion, is considered to be caused by receptor dysfunction. Bone abnormalil cataract and calcium transport defect suggest the abnormal calcium metabolisn MyD. The calcium metabolism is chiefly regulated by parathyroid hormone (PTH). interest in the similarity between MyD and pseudohypoparathyroidism, w h i c h disorder of PTH receptor dysfunction, encouraged the authors to evaluate renal P receptor function from the responses of urinary adenosine 3',5'-monophospl (cAMP) and phosphate excretion after administration of human PTH(1-34). ' responses of cAMP were high in 3 cases, low in one case, but normal in the 4 o~ cases. The phosphaturic responses were elevated in 3 cases, reduced in 3 cases, normal in 2 other cases. Since these abnormal responses closely mimic thos~ hypoparathyroidism, there may also be renal PTH receptor dysfunction in some c," of MyD. The results of the present study suggest another peptide hormone rece1 defect, similar to insulin, which supports the hypothesis of generalised rece1 dysfunction in MyD.
Key words: Myotonic dystrophy ~ Renalparathyroid hormone receptor B Urinary cA excretion
Address for correspondence: Department of Neurology, Nara Medical University, 840 Shijo. Kashihara City, Nara 634, Japan. 0022-510X/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)
340 INTRODUCTION Myotonic dystrophy ( M y D ) is a disease characterized by wasting and weakness of muscles, myotonic reaction as well as other systemic symptoms and signs, especially metabolic or endocrine disturbances (Harper 1979). Recent investigations revealed that the possible etiology o f the disease may be an underlying cellular membrane defect (Brumbak etal. 1981; Fratino etal. 1982; L a m etal. 1983), and insulin receptor abnormality has been demonstrated by several investigators. Moreover, bone deformities, cataract and defect in calcium transport suggest abnormal calcium metabolism in M y D . However, calcium metabolism in this disease has not been investigated intensely, and there have been a few reports about parathyroid function in M y D (Marcel 1930; Bernard-Weil 1972). Thus, the present study was undertaken to elucidate a similarity between M y D and pseudohypoparathyroidism, which is a disorder of parathyroid hormone ( P T H ) receptor dysfunction, as to bone deformities, cataract, mental retardation and myotonic phenomenon. To determine whether P T H receptor is disturbed in M y D , the renal P T H receptor function was investigated from the responses of urinary adenosine 3 ' , 5 ' - m o n o p h o s p h a t e ( c A M P ) and phosphate excretion to human PTH(1-34). SUBJECTS AND METHODS Subjects
The subjects were 8 patients with M y D (5 males and 3 females), ranging in age from 30 to 46 years (mean, 36.6 years) (Table 1). Diagnosis was established on the basis TABLE 1 CLINICAL AND LABORATORY FEATURESIN 8PATIENTS WITH MYOTONIC DYSTROPHY NormalcontrolvNuesarepresentedas m e ~ s ± SEM. No./Sex/Age (yr)
1 / M /
2 3 4 5 6 7 8
/M /M /M /M /F /F /F
/ / / / / / /
46 41 34 33 30 42 34 33
Serum Ca (mg/dl)
P Cr PTH (mg/dl) (mg/dl) (ng/ml)
8.6 8.4 9.3 9.5 8.9 9.1 8.1 8.4
2,1 3,4 4,3 2,7 4.5 2.6 4.5 2.9
0.9 1.0 0.9 1.0 1.0 0.7 0.9 0.9
3.3 + 0.20
0.9 + 0.05
0.5 0.5 0.2 0.2 0.4 0.5 0.3 0.2
Normal controls (n = 9)
34.6
9.2 + 0.07
<0.5
Bone abnormalities on X-ray
Cataract
Mentality
+
+
+ + + + +
+ ? ? + + ? +
normal retarded normal normal retarded retarded retarded normal
341 of clinical signs and symptoms (wasting and weakness of muscles, myotonic reaction, cataract and mental retardation as well as other characteristic systemic dysfunctions), electromyographic t'mdings (myogenic patterns and myotonic discharges) and in some cases pathological findings of the biopsied muscle sho~Jng rather characteristic features. In addition, bone X-rays showed various abnormal findings such as cranial hyperostosis, air sinus enlargement and small pituitary fossa in 6 cases. In the present series, cases 3, 4 and 7 were familial. Control subjects were 9 healthy volunteers age- and sex-matched to patients (5 males and 4 females; average age, 32.2 years). The subjects took no drugs prior to this study and had normal renal function. Informed consent was obtained from each patient and control subject.
Methods Examination was performed in the morning after an overnight fast. Thirty #g of human PTH(1-34) (Niall sequence; Toyo Jozo Inst.) was injected intravenously with saline over a period of 5 rain at 10 : 00 a.m. No significant side-effects were observed in any subjects. Urine was collected at 9:00, 10:00, 10:30, 11:00, 11:30, 12:00 and 13:00. Urine and serum calcium, phosphate and creatinine were measured using a Technicon Autoanalizer ®. Urine cAMP was measured by radioimmunoassay. Since the expression of urinary cAMP and phosphate values differs according to the investigator, we evaluated these values in relation to creatinine ratios, which are not affected by urine volume or by a mistake in urine collection. Statistical analysis was performed by 2-sided tolerance limit test. RESULTS Serum calcium, phosphate, creatinine and PTH levels were normal in all subjects (Table 1).
(1) Basal excretion of urinary cAMP and phosphate (Table 2) The basal excretion of urinary cAMP and phosphate in control subjects was 6.63 + 0.64 nmoles/mg Cr (mean + SEM) and 419.2 + 72.7 #g/mg Cr, respectively. Mean basal urinary cAMP and phosphate in MyD cases were not significantly different from those of controls except in case 5 who showed a slightly elevated basal urinary cAMP level. (2) Renal responses of cAMP and phosphate to human PTH(1-34) (Tables 2 and3) In control subjects, human PTH (1-34) induced a remarkable elevation of urinary cAMP excretion at 30 rain. Increment of cAMP and phosphate were analyzed by the peak to basal ratio (P/B cAMP or phosphate) and the increase from the basal value (,6 cAMP or phosphate). In controls, P/B cAMP and A cAMP were 37.2 + 7.70 and 227.9 + 52.4 umoles/mg Cr, respectively. Phosphaturic responses in control subjects were more blunted than those of cAMP, and the peak values were obtained at 60 min.
342 TABLE 2 URINARY cAMP AND PHOSPHATE EXCRETION BEFORE AND AFTER ADMINISTRATION OF HUMAN PTH(1-34) Case no.
1 2 3 4 5 6 7 8
cAMP
Phosphate
base nmoles/mg Cr
P/B
AcAMP nmoles/mg Cr
base #g/mg Cr
P/B
AP ~tg/mg Cr
5.26 7.44 4.57 6.21 9.34 a 7.40 7.02 6.51
185.1 8.3 72.6 94.2 17.0 31.6 19.5 42.9
968.4 34.5 327.1 578.7 149.9 226.1 129.9 272.7
463 443 660 239 507 650 365 609
5.76 1.02 1.19 5.48 1.33 1.36 1.00 2.02
2,204 26 148 107 167 235 0 619
6.63 8.97 4.29
37.2 65.7 8.7
227.9 420.0 35.8
419.2 686 153
1.73 2.22 1.24
Normal controls
Mean Upper b Lower ~
249.3 438.0 60.1
a Elevated. b Upper and c lower values of 2-sided tolerance limit of control subjects. TABLE 3 SUMMARY OF URINARY cAMP AND PHOSPHATE AFTER ADMINISTRATION OF HUMAN PTH(I-34) IN MYOTONIC DYSTROPHY Case no.
1 2 3 4 5 6 7 8
cAMP
Phosphate
Response type
P/B
AcAMP
P/B
AP
hyper hypo hyper hyper N N N N
hyper hypo N hyper N N N N
hyper hypo hypo hyper N N hypo N
hyper hypo N N N N hypo hyper
IHP-type PHP I-type PHP II-type IHP-type Normal Normal PHP II-type almost normal
Hyper = hyperresponse, hypo = hyporesponse, N = normal response; IHP = idiopathic hypoparathyroidism, PHP = pseudohypoparathyroidism.
P/B phosphate
and
A phosphate
in controls were
1.73 + 0.13
and
249.3 + 51.6
#g/mg Cr, respectively. I n M y D , u r i n a r y r e s p o n s e s o f c A M P a n d p h o s p h a t e v a r i e d in e a c h c a s e . T h u s , c a s e s 1, 3 a n d 4 s h o w e d h y p e r r e s p o n s e s o f c A M P , a n d c a s e 2 s h o w e d a h y p o r e s p o n s e ,
343 whereas cases 5, 6, 7 and 8 were normoresponders. Phosphaturic responses were high in cases 1, 4 and 8, and low in cases 2, 3 and 7, and normal in cases 5 and 6. Here, a hyper- or hyporesponse was taken to be above or below the 95 % 2-sided tolerance limit of controls in either P/B or A values. To summarize the results in Table 3, these response patterns have been classified into four groups: (1)hyperresponse in cAMP and phosphate; (2)hyporesponse in cAMP and phosphate; (3)hyper- or normal response in cAMP but hyporesponse in phosphate; and (4)normal response. DISCUSSION MyD is a systemic disorder considered to be caused by a generalised cellular membrane defect the exact nature of which remains unclear (Brumbak et al. 1981). There have been many reports concerning endocrinological abnormalities in this disease such as abnormal carbohydrate metabolism and insulin secretion (Walsh et al. 1970; Polgar et al. 1972; Tevaarwerk and Hudson 1977), gonadal dysfunction (Harper et al. 1972; Febres et al. 1975; Sagel et al. 1975), low basal metabolic rate with euthyroidism (Drucker et al. 1961; Sagel et al. 1976), elevated growth hormone without acromegaly (Caughey and Koochek 1974) and abnormal growth hormone responses by insulin and arginine infusion (Yamamoto et al. 1974). The abnormal carbohydrate metabolism has been explained by a decrease in affinity of cellular insulin receptor (Kobayashi et al. 1977; Festoff and Moore 1979; Tevaarwerk et al. 1979; Moxley III et al. 1981; Fratino et al. 1982; Lam et al. 1983). Similar receptor dysfunction may underlie diseases involving gonadal hormone, thyroid hormone, growth hormone and PTH. Since peptide hormones act on similar cyclic nucleotide-coupled receptors, it is possible that the basic defect in MyD is a general disturbance in either density or affinity of hormonal receptor throughout the body. From these points of view, it is of interest that MyD has been said to mimic pseudohypoparathyroidism (PHP), which is a disorder of PTH receptor dysfunction (Albright et al. 1942), with regard to cataract, bone deformities, mental retardation and myotonia (mimicking Trousseau's sign). In MyD, cranial hyperostosis, air sinus enlargement, small pituitary fossa as well as metacarpal bone mass loss (Spengos et al. 1980) suggest a widespread abnormality in calcium metabolism. However, details about the nature of this abnormality or parathroid function in this disease are not clear. Thus, the renal PTH receptor function in MyD was also a focus of investigation. PTH has been said to act in the proximal renal tubule to inhibit resorption of phosphate resulting in increment of urinary phosphate excretion. In addition, it has been clarified that there is PTH-sensitive adenylate cyclase, PTH receptor, in the proximal tubule, and that PTH activates this enzyme to produce cAMP (Chase and Aurbach 1967; Rusmussen and Tenenhouse 1968; Aurbach and Heath 1974; Shlatz et al. 1975). Administration of PTH to normal subjects results in a remarkable rise in urinary cAMP that precedes the phosphaturic response (Chase and Aurbach 1967; Potts et al. 1971; Kurokawa et al. 1974; Tomlinson et al. 1974). On the other hand, PTH, the first messenger, increases permeability of the target
344 cell membrane to calcium ions and thereby increases cellular uptake of calcium which acts as a second messenger. Simultaneously, PTH stimulates adenosine triphosphate to manufacture cAMP in the cytoplasm, cAMP, acting as another second messenger, stimulates specific protein kinases which control the activity of other enzyme systems by phosphorylation of specific proteins (Habener and Potts 1978). Alternatively, hypoparathyroidism is divided into two groups according to the responses of urinary cAMP and phosphate to extrinsic PTH. One is idiopathic hypoparathyroidism (IHP) which is caused by inexplicable PTH secretion; the other is PHP, a disease of PTH receptor dysfunction. There are two types of PHP, type I and type II. In the former, renal PTH receptor is almost completely disturbed, so urinary cAMP and phosphate responses are very blunted (Chase et al. 1969); in the latter, however, renal adenylate cyclase is intact although action of PTH distal to the cAMP step is disturbed, and so considerable cAMP excretion is observed without phosphaturic response (Drezner et al. 1973). Still, IHP shows remarkable responses of urinary cAMP and phosphate because circulating PTH is negligibly low. As previously reported, the PTH administration test is very useful for differentiating these three types of hypoparathyroidism and also reveals the renal PTH receptor function (Konagaya et al. 1981). According to these classifications, the responses of the present 8 cases may be evaluated as follows. Cases 1 and 4 showed IHP-like responses, cases 2 and 7 indicated type I PHP-like response, cases 3 and 7 presented type II PHP-like responses, and cases 5, 6 and 8 were normo-responders. The reason why the responses were so different in each case is not clear, but it could be considered that the PTH receptor differs either in number or sensitivity. In IHP-like responders there may be hypersensitivity or an increased number of receptors, and in PHP-like responders, an insensitivity or reduced number of receptors. The 8 cases under study had normal parathyroid function because of normal serum calcium, phosphorus and PTH levels. Therefore, the abnormal renal PTH receptor function is not due to parathyroid dysfunction but suggests a membrane defect of PTH similar to insulin. It has also been demonstrated in MyD that there is abnormal phosphorylation of membrane protein (Roses and Appel 1973; 1975) and reduced activity of adenyl cyclase in the sarcolemmal membrane (Reddy et al. 1977) or a defect in calcium transport (increased rate of calcium accumulation and efflux in the red blood cells) (Seiler and Kuhn 1970; Plishker and Gitelman 1978), suggesting that a change in membrane permeability rather than a specific transport defect is the cause. Therefore, the abnormal phosphorylation of membrane protein may well be caused by the PTH dysfunction. The present results provide evidence indicating the generalised membrane defect in MyD, and assist in understanding the pathogenesis of this disorder. ACKNOWLEDGEMENT We are grateful to Toyo Jozo Institute for the gift of human PTH(1-34).
345 REFERENCES Albright, F., C.H. Burnett, P.H. Smith and W. Parson (1942) Pseudohypoparathyroidism - - an example of "Seabright-Bantam syndrome ~ - - Report of three eases, Endocrinology, 30: 922-932. Aurbach G.D. and D.A. Heath (1974) Parathyroid hormone and caleitonin regulation of renal function, Kidney International, 6: 331-345. Bernard-Weft, E. (1972) Donn6es neuro-endocriniennes nouvelles sur la maladie Steinert, particuli6rement en ce qui eoncerne l'axe hypothalamohypophysio-surr6nalien et la r6gulation du m6tabolisme phosphocalcique, Ann. d'Endocrinol. (Paris), 33: 251-266. Brumbak, R.K., K.M. Carlson, H. Wilson and R.D. Staton (1981) Myotonic dystrophy as a disease of abnormal membrane receptors - - A hypothesis of pathophysiology and a new approach to treatment, Medical Hypothesis, 7: 1059-1066. Caughey J. E. and M.H. Koochek (1974) Growth hormone in dystrophia myotonica, New Zealand Med. J., 79: 685-687. Chase L.R. and G.D. Aurbach (1967) Parathyroid function and the renal excretion of 3',5'-adenylic acid, Proc. Nat. Acad. Sci. (USA), 58: 581-525. Chase L.R., G. L. Melson and G.D. Aurbaeh (1969) Pseudohypoparathyroidism - - Defective excretion of 3',5'-AMP in response of parathyroid hormone, J. Clin. Invest., 48:1832-1844. Drucker W. D., L. P. Lowland, K. Sterling and N. P. Christy (1961) On the function of the endocrine glands in myotonic muscular dystrophy, Amer. d. Med., 31: 941-950. Drezner M., F. A. Neelon and H. E. Lebovitz (1973) Pseudohypoparathyroidism type II - - A possible defect in the reception of the cyclic AMP signal, N. Engl. J. Med., 289: 1056-1060. Febres F., H. Scaglia, R. Lisker, J. Epinosa, T. Morato, M. Shlurovich and G. Perex-Paracios (1975) Hypothalamic-pituitary-gonadal function in patients with myotonic dystrophy, J. Clin. Endocrinol. Metab., 41: 833-840. FestoffB. W. and W. V. Moore (1979) Evaluation of the insulin receptor in myotonic dystrophy. Ann. NeuroL, 6: 60-65. Fratino P., G. Bellomo, R. Bellazzi, E. Martignoni and G. Nappi (1982) Insulin receptors in myotonic dystrophy. Acta Neurol. Belg., 82: 128-137. Habener J. F. and J.T. Potts Jr. (1978) Parathyroid phisiology and primary hyperparathyroidism. In: L.V. Avioli and S.M. Krane (Eds.), Metabolic Bone Disease, Vol. 2, Academic Press, New York, pp. 1-147. Harper P., R. Penny, T.P. Foley, C.J. Migeon and R.M. Blizzard (1972) Gonadal function in males with myotonic dystrophy, J. Clin. Edocrinol. Metab., 35: 852-856. Harper P. S. (1979)In: J.N. Walton (Ed.), Myotonic Dystrophy, W.B. Saunders, Philadelphia. Kobayashi M., J.C. Meek and E. Streib (1977) The insulin receptor in myotonic dystrophy, J. Clin. Endocrinol. Metab., 45: 821-824. Konagaya Y., K. Takatsuki and A. Tomita (1981) Effects of synthetic human parathyroid hormone (1-34) on plasma and urinary adenosine 3' ,5'-monophosphate and urinary phosphate and calcium in patients with hypoparathyroidism and pseudohypoparathyroidism, Folia Endocrinol. Jap., 57:1591-1608. Kurokawa K., N. Nagata, M. Sasaki and K. Nakane (1974) Effects of calcitonin on the concentration of cyclic adenosine 3' ,5'-monophosphate in rat kidney in vivo and in vitro, Endocrinology, 94: 1514-1518. Lam L., A.J. Hudson, K. P. Strickland and G. J. M. Tevaarwerk (1983) Insulin binding to myotonic dystophy fibroblasts, J. Neurol. Sci., 58: 289-295. Marcel M. (1930) Dystrophie myotonique et insuffisance parathyroidienne, Bull. M~m. Soc. H6p. Paris, 46: 534-535. Moxley III, R.T., J. N. Livingston, D.H. Lockwood, R. C. Griggs and R.L. Hill (1981) Abnormal regulation of monocyte insulin-binding affinity after glucose ingestion in patients with myotonic dystrophy, Proc. Nat. Acad. Sci. (USA), 78: 2567-2571. Plishker G.A. and H.J. Gitelman (1978) Myotonic muscular dystrophy - - Altered calcium transport in erythrocytes, Science, 200: 323-325. Polgar J.G., W.G. Bradley, A.R.M. Upton, J. Anderson, J.M.L. Howat, F. Petito, D.F. Roberts and J. Scopa (1972) The early detection of dystrophia myotonica, Brain, 95: 761-776. Potts Jr. J.T., G. W. Tregear, H.T. Keutmann, H. D. Niall, R. Sauer, L.J. Defto, B. F. Dowson, M. L. Hogan ~nd G.D. Aurbach (1971) Synthesis of a biologically active N-terminal tetratriacontapeptide of parathyroid hormone, Proc. Nat. Acad. Sci. (USA), A' : 63-67. Reddy N. M., K. L. Oliver and W. K. Engel (1977) Alterations in the sarcolemmal adenylate cyclase activity (AC-D) in myotonia, Neurology (Minneap.), 8: 378-379. Roses A.D. and S.H. Appel (1973) Protein kinase activity in erythrocyte gohsts of patients with myotonic muscular dystrophy, Proc. Nat. Acad. Sci. (USA), (Wash.), 70: 1855-1859. Roses A.D. and S.H. Appel (1973) Protein kinase activity in erythrocyte ghosts of patients with myotonic muscular dystrophy, Proc. Nat. Acad. Sci. (USA), (Wash.), 70: 1855-1859.
346 Roses A.D. and S. H. Appel (1975) Phosphorylation of component a of the human erythrocyte membrane in myotonic muscular dystrophy, J. Membr. Biol., 20: 51-58. Rusmussen H. and A. Tenenhouse (1968) Cyclic adenosine monophosphate, Ca + +, and membranes, Proc. Nat. Acad. Sci. (USA), 59: 1364-1370. Sagel J., L.A. Distiller, J.E. Morley and H. Issacs (1975) Myotonia d y s t r o p h i c a - Studies on gonadal function using luteinizing hormone-releasing hormone (LRH), J. Clin. Endocrinol. Metab., 40: 1110-1113. S agel J., L.A. Distiller, J.E. Morley and H. Issacs (1976) Normal thyrotropin-releasing hormone response in myotonia dystrophica, Arch. Neurol. (Chic.), 33: 520. Seller D. and E. Kuhn (1970) Kalzium Transport der isolierten Vesikel des sarkoplasmatischen Retikulums von Patienten mit Myotonia congenita und Myotonia dystrophica, Schweiz Med. Wschr., 100: 1374-1376. Shlatz L.J., I.L. Schwartz, K.I. Saffran and R. Kinne (1975) Distribution of parathyroid hormonestimulated adenylate cyclase in plasma membranes of cells of the kidney cortex, J. Membr. Biol., 24: 131-144. Spengos M., M. Hadjiconstantinou, D. Vassilopoulos and S. Scarpalezos (1980) Myotonic dystrophy - Bone mass loss? IRCS Med. Sci., 8: 13. Tevaarwerk G. J. M. and A.J. Hudson (1977) Carbohydrate metabolism and insulin resistance in myotonia dystrophica, J. Clin. Endocrinol. Metab., 44: 491-498. Tevaarwerk G.J.M., K.P. Strickland, C.-H. Lin and A.J. Hudson (1979) Studies on insulin resistance and insulin receptor binding in myotonia dystrophica, J. Clin. EndocrinoL Metab., 49: 216-222. Tomlinson S., P.M. Barling, J.D.M. Albano, B.L. Brown and J.L.H. O'Riordan (1974) The effects of exogenous parathyroid hormone on plasma and urinary adenosine 3' ,5'-cyclic monophosphate in man, Clin. Sci. Mol. Med., 47: 481-492. Walsh J. C., J. R. Turtle, S. Miller and J.G. McLeod (1970) Abnormalities of insulin secretion in dystrophia myotonica, Brain, 93: 731-742. Y amamoto M., S. Kito, N. Fujimori and K. Kosaka (1974) Endocrinological studies on myotonic dystrophy, Clin. Neurol (Tokyo), 14: 406-414.
Evaluation of Renal Parathyroid Hormone Recept Function in Myotonic Dystrophy Yoko Konagaya, Masaaki Konagaya, Yukio Mano, Tetsuya Takayanagi Akio Tomita t Department of Neurology, Nara Medical University, and 1First Department of Internal Medicine, Na University School of Medicine, Nagoya (Japan) (Received 6 December, 1984) (Revised, received 4 June, 1985) (Accepted 7 June, 1985)
SUMMARY
Endocrine abnormalities in myotonic dystrophy (MyD) reflect some of the m systemic involvement resulting from this disorder. One of these, abnormal ins secretion, is considered to be caused by receptor dysfunction. Bone abnormalil cataract and calcium transport defect suggest the abnormal calcium metabolisn MyD. The calcium metabolism is chiefly regulated by parathyroid hormone (PTH). interest in the similarity between MyD and pseudohypoparathyroidism, w h i c h disorder of PTH receptor dysfunction, encouraged the authors to evaluate renal P receptor function from the responses of urinary adenosine 3',5'-monophospl (cAMP) and phosphate excretion after administration of human PTH(1-34). ' responses of cAMP were high in 3 cases, low in one case, but normal in the 4 o~ cases. The phosphaturic responses were elevated in 3 cases, reduced in 3 cases, normal in 2 other cases. Since these abnormal responses closely mimic thos~ hypoparathyroidism, there may also be renal PTH receptor dysfunction in some c," of MyD. The results of the present study suggest another peptide hormone rece1 defect, similar to insulin, which supports the hypothesis of generalised rece1 dysfunction in MyD.
Key words: Myotonic dystrophy ~ Renalparathyroid hormone receptor B Urinary cA excretion
Address for correspondence: Department of Neurology, Nara Medical University, 840 Shijo. Kashihara City, Nara 634, Japan. 0022-510X/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)
340 INTRODUCTION Myotonic dystrophy ( M y D ) is a disease characterized by wasting and weakness of muscles, myotonic reaction as well as other systemic symptoms and signs, especially metabolic or endocrine disturbances (Harper 1979). Recent investigations revealed that the possible etiology o f the disease may be an underlying cellular membrane defect (Brumbak etal. 1981; Fratino etal. 1982; L a m etal. 1983), and insulin receptor abnormality has been demonstrated by several investigators. Moreover, bone deformities, cataract and defect in calcium transport suggest abnormal calcium metabolism in M y D . However, calcium metabolism in this disease has not been investigated intensely, and there have been a few reports about parathyroid function in M y D (Marcel 1930; Bernard-Weil 1972). Thus, the present study was undertaken to elucidate a similarity between M y D and pseudohypoparathyroidism, which is a disorder of parathyroid hormone ( P T H ) receptor dysfunction, as to bone deformities, cataract, mental retardation and myotonic phenomenon. To determine whether P T H receptor is disturbed in M y D , the renal P T H receptor function was investigated from the responses of urinary adenosine 3 ' , 5 ' - m o n o p h o s p h a t e ( c A M P ) and phosphate excretion to human PTH(1-34). SUBJECTS AND METHODS Subjects
The subjects were 8 patients with M y D (5 males and 3 females), ranging in age from 30 to 46 years (mean, 36.6 years) (Table 1). Diagnosis was established on the basis TABLE 1 CLINICAL AND LABORATORY FEATURESIN 8PATIENTS WITH MYOTONIC DYSTROPHY NormalcontrolvNuesarepresentedas m e ~ s ± SEM. No./Sex/Age (yr)
1 / M /
2 3 4 5 6 7 8
/M /M /M /M /F /F /F
/ / / / / / /
46 41 34 33 30 42 34 33
Serum Ca (mg/dl)
P Cr PTH (mg/dl) (mg/dl) (ng/ml)
8.6 8.4 9.3 9.5 8.9 9.1 8.1 8.4
2,1 3,4 4,3 2,7 4.5 2.6 4.5 2.9
0.9 1.0 0.9 1.0 1.0 0.7 0.9 0.9
3.3 + 0.20
0.9 + 0.05
0.5 0.5 0.2 0.2 0.4 0.5 0.3 0.2
Normal controls (n = 9)
34.6
9.2 + 0.07
<0.5
Bone abnormalities on X-ray
Cataract
Mentality
+
+
+ + + + +
+ ? ? + + ? +
normal retarded normal normal retarded retarded retarded normal
341 of clinical signs and symptoms (wasting and weakness of muscles, myotonic reaction, cataract and mental retardation as well as other characteristic systemic dysfunctions), electromyographic t'mdings (myogenic patterns and myotonic discharges) and in some cases pathological findings of the biopsied muscle sho~Jng rather characteristic features. In addition, bone X-rays showed various abnormal findings such as cranial hyperostosis, air sinus enlargement and small pituitary fossa in 6 cases. In the present series, cases 3, 4 and 7 were familial. Control subjects were 9 healthy volunteers age- and sex-matched to patients (5 males and 4 females; average age, 32.2 years). The subjects took no drugs prior to this study and had normal renal function. Informed consent was obtained from each patient and control subject.
Methods Examination was performed in the morning after an overnight fast. Thirty #g of human PTH(1-34) (Niall sequence; Toyo Jozo Inst.) was injected intravenously with saline over a period of 5 rain at 10 : 00 a.m. No significant side-effects were observed in any subjects. Urine was collected at 9:00, 10:00, 10:30, 11:00, 11:30, 12:00 and 13:00. Urine and serum calcium, phosphate and creatinine were measured using a Technicon Autoanalizer ®. Urine cAMP was measured by radioimmunoassay. Since the expression of urinary cAMP and phosphate values differs according to the investigator, we evaluated these values in relation to creatinine ratios, which are not affected by urine volume or by a mistake in urine collection. Statistical analysis was performed by 2-sided tolerance limit test. RESULTS Serum calcium, phosphate, creatinine and PTH levels were normal in all subjects (Table 1).
(1) Basal excretion of urinary cAMP and phosphate (Table 2) The basal excretion of urinary cAMP and phosphate in control subjects was 6.63 + 0.64 nmoles/mg Cr (mean + SEM) and 419.2 + 72.7 #g/mg Cr, respectively. Mean basal urinary cAMP and phosphate in MyD cases were not significantly different from those of controls except in case 5 who showed a slightly elevated basal urinary cAMP level. (2) Renal responses of cAMP and phosphate to human PTH(1-34) (Tables 2 and3) In control subjects, human PTH (1-34) induced a remarkable elevation of urinary cAMP excretion at 30 rain. Increment of cAMP and phosphate were analyzed by the peak to basal ratio (P/B cAMP or phosphate) and the increase from the basal value (,6 cAMP or phosphate). In controls, P/B cAMP and A cAMP were 37.2 + 7.70 and 227.9 + 52.4 umoles/mg Cr, respectively. Phosphaturic responses in control subjects were more blunted than those of cAMP, and the peak values were obtained at 60 min.
342 TABLE 2 URINARY cAMP AND PHOSPHATE EXCRETION BEFORE AND AFTER ADMINISTRATION OF HUMAN PTH(1-34) Case no.
1 2 3 4 5 6 7 8
cAMP
Phosphate
base nmoles/mg Cr
P/B
AcAMP nmoles/mg Cr
base #g/mg Cr
P/B
AP ~tg/mg Cr
5.26 7.44 4.57 6.21 9.34 a 7.40 7.02 6.51
185.1 8.3 72.6 94.2 17.0 31.6 19.5 42.9
968.4 34.5 327.1 578.7 149.9 226.1 129.9 272.7
463 443 660 239 507 650 365 609
5.76 1.02 1.19 5.48 1.33 1.36 1.00 2.02
2,204 26 148 107 167 235 0 619
6.63 8.97 4.29
37.2 65.7 8.7
227.9 420.0 35.8
419.2 686 153
1.73 2.22 1.24
Normal controls
Mean Upper b Lower ~
249.3 438.0 60.1
a Elevated. b Upper and c lower values of 2-sided tolerance limit of control subjects. TABLE 3 SUMMARY OF URINARY cAMP AND PHOSPHATE AFTER ADMINISTRATION OF HUMAN PTH(I-34) IN MYOTONIC DYSTROPHY Case no.
1 2 3 4 5 6 7 8
cAMP
Phosphate
Response type
P/B
AcAMP
P/B
AP
hyper hypo hyper hyper N N N N
hyper hypo N hyper N N N N
hyper hypo hypo hyper N N hypo N
hyper hypo N N N N hypo hyper
IHP-type PHP I-type PHP II-type IHP-type Normal Normal PHP II-type almost normal
Hyper = hyperresponse, hypo = hyporesponse, N = normal response; IHP = idiopathic hypoparathyroidism, PHP = pseudohypoparathyroidism.
P/B phosphate
and
A phosphate
in controls were
1.73 + 0.13
and
249.3 + 51.6
#g/mg Cr, respectively. I n M y D , u r i n a r y r e s p o n s e s o f c A M P a n d p h o s p h a t e v a r i e d in e a c h c a s e . T h u s , c a s e s 1, 3 a n d 4 s h o w e d h y p e r r e s p o n s e s o f c A M P , a n d c a s e 2 s h o w e d a h y p o r e s p o n s e ,
343 whereas cases 5, 6, 7 and 8 were normoresponders. Phosphaturic responses were high in cases 1, 4 and 8, and low in cases 2, 3 and 7, and normal in cases 5 and 6. Here, a hyper- or hyporesponse was taken to be above or below the 95 % 2-sided tolerance limit of controls in either P/B or A values. To summarize the results in Table 3, these response patterns have been classified into four groups: (1)hyperresponse in cAMP and phosphate; (2)hyporesponse in cAMP and phosphate; (3)hyper- or normal response in cAMP but hyporesponse in phosphate; and (4)normal response. DISCUSSION MyD is a systemic disorder considered to be caused by a generalised cellular membrane defect the exact nature of which remains unclear (Brumbak et al. 1981). There have been many reports concerning endocrinological abnormalities in this disease such as abnormal carbohydrate metabolism and insulin secretion (Walsh et al. 1970; Polgar et al. 1972; Tevaarwerk and Hudson 1977), gonadal dysfunction (Harper et al. 1972; Febres et al. 1975; Sagel et al. 1975), low basal metabolic rate with euthyroidism (Drucker et al. 1961; Sagel et al. 1976), elevated growth hormone without acromegaly (Caughey and Koochek 1974) and abnormal growth hormone responses by insulin and arginine infusion (Yamamoto et al. 1974). The abnormal carbohydrate metabolism has been explained by a decrease in affinity of cellular insulin receptor (Kobayashi et al. 1977; Festoff and Moore 1979; Tevaarwerk et al. 1979; Moxley III et al. 1981; Fratino et al. 1982; Lam et al. 1983). Similar receptor dysfunction may underlie diseases involving gonadal hormone, thyroid hormone, growth hormone and PTH. Since peptide hormones act on similar cyclic nucleotide-coupled receptors, it is possible that the basic defect in MyD is a general disturbance in either density or affinity of hormonal receptor throughout the body. From these points of view, it is of interest that MyD has been said to mimic pseudohypoparathyroidism (PHP), which is a disorder of PTH receptor dysfunction (Albright et al. 1942), with regard to cataract, bone deformities, mental retardation and myotonia (mimicking Trousseau's sign). In MyD, cranial hyperostosis, air sinus enlargement, small pituitary fossa as well as metacarpal bone mass loss (Spengos et al. 1980) suggest a widespread abnormality in calcium metabolism. However, details about the nature of this abnormality or parathroid function in this disease are not clear. Thus, the renal PTH receptor function in MyD was also a focus of investigation. PTH has been said to act in the proximal renal tubule to inhibit resorption of phosphate resulting in increment of urinary phosphate excretion. In addition, it has been clarified that there is PTH-sensitive adenylate cyclase, PTH receptor, in the proximal tubule, and that PTH activates this enzyme to produce cAMP (Chase and Aurbach 1967; Rusmussen and Tenenhouse 1968; Aurbach and Heath 1974; Shlatz et al. 1975). Administration of PTH to normal subjects results in a remarkable rise in urinary cAMP that precedes the phosphaturic response (Chase and Aurbach 1967; Potts et al. 1971; Kurokawa et al. 1974; Tomlinson et al. 1974). On the other hand, PTH, the first messenger, increases permeability of the target
344 cell membrane to calcium ions and thereby increases cellular uptake of calcium which acts as a second messenger. Simultaneously, PTH stimulates adenosine triphosphate to manufacture cAMP in the cytoplasm, cAMP, acting as another second messenger, stimulates specific protein kinases which control the activity of other enzyme systems by phosphorylation of specific proteins (Habener and Potts 1978). Alternatively, hypoparathyroidism is divided into two groups according to the responses of urinary cAMP and phosphate to extrinsic PTH. One is idiopathic hypoparathyroidism (IHP) which is caused by inexplicable PTH secretion; the other is PHP, a disease of PTH receptor dysfunction. There are two types of PHP, type I and type II. In the former, renal PTH receptor is almost completely disturbed, so urinary cAMP and phosphate responses are very blunted (Chase et al. 1969); in the latter, however, renal adenylate cyclase is intact although action of PTH distal to the cAMP step is disturbed, and so considerable cAMP excretion is observed without phosphaturic response (Drezner et al. 1973). Still, IHP shows remarkable responses of urinary cAMP and phosphate because circulating PTH is negligibly low. As previously reported, the PTH administration test is very useful for differentiating these three types of hypoparathyroidism and also reveals the renal PTH receptor function (Konagaya et al. 1981). According to these classifications, the responses of the present 8 cases may be evaluated as follows. Cases 1 and 4 showed IHP-like responses, cases 2 and 7 indicated type I PHP-like response, cases 3 and 7 presented type II PHP-like responses, and cases 5, 6 and 8 were normo-responders. The reason why the responses were so different in each case is not clear, but it could be considered that the PTH receptor differs either in number or sensitivity. In IHP-like responders there may be hypersensitivity or an increased number of receptors, and in PHP-like responders, an insensitivity or reduced number of receptors. The 8 cases under study had normal parathyroid function because of normal serum calcium, phosphorus and PTH levels. Therefore, the abnormal renal PTH receptor function is not due to parathyroid dysfunction but suggests a membrane defect of PTH similar to insulin. It has also been demonstrated in MyD that there is abnormal phosphorylation of membrane protein (Roses and Appel 1973; 1975) and reduced activity of adenyl cyclase in the sarcolemmal membrane (Reddy et al. 1977) or a defect in calcium transport (increased rate of calcium accumulation and efflux in the red blood cells) (Seiler and Kuhn 1970; Plishker and Gitelman 1978), suggesting that a change in membrane permeability rather than a specific transport defect is the cause. Therefore, the abnormal phosphorylation of membrane protein may well be caused by the PTH dysfunction. The present results provide evidence indicating the generalised membrane defect in MyD, and assist in understanding the pathogenesis of this disorder. ACKNOWLEDGEMENT We are grateful to Toyo Jozo Institute for the gift of human PTH(1-34).
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