LETTERS TO THE EDITOR
Comment on Calcium-Regulated Renal Calcium Handling in Healthy Menª
To the editor:
Dr. Fuleihan and her colleagues (1) found that the relationship be- tween urinary calcium excretion and plasma calcium during a PTH clamp was broadly similar to that previously observed without the clamp. This is an important new finding, indicating that acute changes in PTH secretion have little effect on tubular reabsorption of calcium and that unclamped calcium infusions can give useful information.
However, the authors’ fascination with sigmoid curves has misled them about basic renal physiology (2). When the amount of ion per unit of glomerular filtrate (GFR) is plotted against plasma level then, absent a change in GFR, the amount filtered is given by a straight line through the origin of slope unity. For tubular maximum limited substances such as glucose, the amount excreted is given by a line that is curvilinear at the lower end (the splay segment) and parallel to the line of filtration at the upper end. The plasma level dividing these segments is the saturation threshold, so-called because, above that level, the amount reabsorbed (filtered minus excreted) is constant, reflecting saturation of a tubular transport process.
If, as is implied by a sigmoid curve, the amount of calcium excreted reaches a plateau, than absent a change in GFR, the amount reabsorbed will increase without limit as plasma calcium rises, the opposite to what is predicted by the authors’ model in Fig. 7. We suggest three possible ex- planations for this paradox. First, in Fig. 3, the inference of a sigmoid relationship, rather than a linear relationship above the splay segment, rests on only two points. Second, if creatinine clearance, which was not reported, fell during the infusion, then calcium reabsorption may not have increased. Third, the natriuretic effect of calcium may have induced sufficient sodium deficiency during the infusion to have increased both sodium and calcium reabsorption. We believe the third explanation is the most likely.
A. M. Parfitt and S. Adami University of Arkansas for Medical Sciences Little Rock, Arkansas 72205
References
1. Fuleihan GE, Seifter J, Scott J, Brown EM. 1998 Calcium-regulated renal calcium handling in healthy men: relationship to sodium handling. J Clin Endocrinol Metab. 83:2366-2372.
2. Parfitt AM, Kleerekoper M. 1980 The divalent ion homeostatic system: Phys- iology and metabolism of calcium, phosphorus, magnesium and bone. In: Maxwell M, Kleeman CR, eds. Clinical Disorders of Fluid and Electrolyte Metabolism, 3rd ed. New York: McGraw Hill; 269-398.
Calcium-Regulated Renal Calcium Handling in Healthy Men-Authors’ Responseb
To the editor:
Drs. Parfitt and Adami raise several interesting points in their letter above. Regarding the sigmoidal curves relating urinary excretion of Ca, Mg, and Na to serum Ca, our curve was fitted by a “mechanism-blind” computer program (1). While the data for Mg, Ca, and Na excretion on the low Na diet were not clearly sigmoidal, those for both Ca and Na excretion flattened out at higher serum Ca levels on the high Na diet. Moreover, the excretion rate for Mg became nearly constant above 1.6
mM Ca. Independent of the mechanism(s) involved, these sigmoidal curves approximate the data very closely (r2 > 0.9) on the high Na diet. While this may not square with the tenets of classic renal physiology, these were the results observed.
The issue then becomes understanding the difference between our observations and standard physiological teaching. In light of earlier work (2) on familial hypocalciuric hypercalcemia (FHH), which is caused by heterozygous inactivating mutations in the calcium-sensing receptor (CaR) (3), our results, coupled with the CaR’s localization and function along the nephron (4), argue that CaR-mediated inhibition of Na, Mg, and Ca reabsorption in the thick ascending limb (TAL) can explain Ca-induced increases in the excretion of these three ions (3). Attie et al. (2) has shown that parathyroidectomized patients with FHH exhibit marked flattening of the relationship between serum and urine Ca compared to those with hypoparathyroidism alone. This result strongly supports a key role for the CaR in mediating hypercalcemia-induced calciuria. We postulate that the normally steep slope of urine Ca on serum urine Ca does not so much reflect “saturation” of Ca reabsorption, with resultant “overflow” of urinary Ca, as it does CaR-mediated in- hibition of this reabsorption. Persons with FHH also lack the usual natriuretic response to hypercalcemia, further implicating a renal action of the CaR at a site where Na and Ca handling are coupled, presumably the TAL (3). In the case of serum Ca-induced changes in urinary Mg and Na, because serum level of Na and Mg did not change during our study, their urinary excretion presumably plateaus at levels of serum Ca max- imally stimulating the CaR, which occur at about 1.4-1.5 mM for CaR- mediated inhibition of PTH secretion.
Why doesn’t CaR-mediated inhibition of tubular Ca reabsorption produced a steeper, but still linear increase in Ca excretion? In studies performed in vivo, all relevant mechanism(s) cannot be dissected out; we agree with Drs. Parfitt and Adami that multiple factors may be at work. Ca-induced natriuresis may deplete plasma volume sufficiently to in- crease tubular Ca reabsorption, contributing to the curve’s sigmoidal shape. However, in the first two subjects studied in our clearance pro- tocols, both PAH and inulin clearances were similar at the beginning and end of the citrate and calcium infusions, during both low salt and high salt protocols. Furthermore, in another study using a similar protocol, renal blood flow, as measured with para-aminohippurate clearance, was unchanged during either the calcium or the EDTA infusion in patients on a low-salt diet (5).
Complicating the situation further is the CaR’s presence elsewhere along the nephron [i.e. proximal and distal convoluted tubule and mac- ula densa (4)], where it could also modulate Ca, Mg, and Na reabsorp- tion. Additional studies utilizing existing transgenic models (e.g. mice with knockout of the CaR) and/or specific CaR agonists (6) or antag- onists (7) will likely clarify further the CaR’s role in renal solute and water handling. Classic renal physiology, while based largely on “black- box” analyses of renal reabsorptive processes, has provided invaluable models for understanding renal function in the intact organism. The molecular tools are now available, however, for characterizing the mech- anisms underlying renal tubular transport and relating these to in vivo observations.
Ghada El-Hajj Fuleihan Calcium Metabolism and Osteoporosis Program American University of Beirut Medical Center Beirut, Lebanon
Edward M. Brown, and Julian Seifter Divisions of Endocrinology (E.M.B.) and Nephrology (J.S.) Brigham and Women’s Hospital Boston, Massachusetts
References
1. El-Hajj Fuleihan G, Seifter J, Scott J, Brown EM 1998 Calcium-regulated renal calcium handling in healthy men: relationship to sodium handling. J Clin Endocrinol Metab. 83:2366-2372.
ª Received October 23, 1998. Address correspondence to: A.M. Parfitt, M.D., Professor of Medicine, University of Arkansas for Medical Sci- ences 4301 W. Markham St. Slot 587, Little Rock, Arkansas 72205-7199.
b Received January 12, 1999. Address correspondence to: Ghada El- Hajj Fuleihan, M.D., M.P.H., Director, Calcium Metabolism and Osteo- porosis Program, American University of Beruit Medical Center, Bliss Street, P.O. Box 113-6044 Beirut, Lebanon.
2. Attie MF, Gill Jr J, Stock JL, et al. 1983 Urinary calcium excretion in familial hypocalciuric ypercalcemia. Persistence of relative hypocalciuria after induc- tion of hypoparathyroidism. J Clin Invest. 72:667-676.
3. Hebert SC, Brown EM, Harris HW 1997 Role of the Ca2+-sensing receptor in divalent mineral ion homeostasis. J Exp Biol. 200:295-302.
4. Riccardi D, Hall AE, Chattopadhyay, et al. 1998 Localization of the extracel- lular Ca2+/polyvalent cation)-sensing receptor protein in rat kidney. Am J Physiol. 274:F611-F622.
5. Porter L, Conlin PR, Scott J, Brown EM, El-Hajj Fuleihan G. Calcium mod- ulation of the renin-aldosterone axis. J Endocrinol Invest. In press.
6. Silverberg SJ, Bone III HG, Marriott TB, et al. 1997 Short-term inhibition of parathyroid hormone secretion by a calcium-receptor agonist in patients with primary hyperparathyroidism. N Engl J Med. 337:1506-1510.
7. Nemeth EF, Fax J, Delmar EG, et al. 1998 Stimulation of parathyroid hormone secretion by a small molecule antagonist of the calcium receptor. J Bone Miner Res. 13:S156 (Abstract 1030).
Comment-Is There a Role for Low Doses of Mitotane (o,p’-DDD) as Adjuvant Therapy in Adrenocortical Carcinoma?”
To the editor:
The paper by Dickstein et al. (1) describes four patients with localized adrenocortical carcinoma who received low-dose (1.5-2.0 g/day) adju- vant mitotane therapy postoperatively and continued the drug during follow-up. Of these patients, two remained disease-free 57 and 21 months after surgery, one died of an unrelated reason 68 months after surgery, and one developed lung metastases 48 months after surgery. Notwithstanding the limited number of patients examined, the authors conclude that low doses of mitotane might improve disease-free survival in adrenocortical carcinoma.
The role of mitotane as adjuvant treatment for adrenocortical carci- noma is controversial (1-8). Our experience with adjuvant mitotane (8), as that of others (3-6), indicates that it is not beneficial in terms of either disease freedom or survival.
We expanded our observation, and, of 59 consecutive patients (36 females, 23 males) with adrenocortical carcinoma (34 functioning and 25 nonfunctioning), 26 (44%) with localized or regional disease (me- dian tumor size, 8.0 cm; range, 4.6-25.0 cm) underwent complete resection of the tumoral mass. Of these, 11 patients (group 1: 7 females and 4 males) received mitotane (o,p’-DDD, Lysodren, Bristol-Myers Squibb) postoperatively at doses of 4-8 g daily, whereas 15 patients (group 2: 9 females and 6 males) were given no medical treatment. The two groups were similar with regard to sex, age, tumor size, functional status, and tumor staging at diagnosis. Six patients of group 1 were free of disease at last follow-up (range: 6-82 months after surgery), and 5 developed metastases or recurrences (disease free-intervals of 4-29 months); 3 of them died of the disease 24-40 months after diagnosis. Of group 2, 6 were free of disease at last follow-up (range, 14-74 months after surgery), and 9 developed metastases (disease free-intervals of 8-60 months), 8 of them died during follow-up (survival: 15-104 months). Cumulative disease-free interval and survival rates, estimated with the Kaplan-Meyer method and compared with the log-rank test, were not significantly different between the two groups (x2 = 0.26, df = 1, P NS; and x2 = 1.15, df = 1, P NS, respectively; Fig. 1). Owing to these disappointing results and the side-effects of mitotane, which significantly worsen quality of life of patients, we would not advocate mitotane as adjuvant treatment of adrenocortical carcinoma. However, prospective studies are needed to evaluate the real efficacy of this compound.
Luisa Barzon, Francesco Fallo, Nicoletta Sonino, Otello Daniele, and Marco Boscaro University of Padova City Hospital of Padova Padova 35128, Italy
” Received January 7, 1999. Address correspondence to: Luisa Barzon, Division of Endocrinology, Institute of Semeiotica Medica, Via Ospedale 105, Padova 35128, Italy.
100
Adjuvant mitotane
80
No treatment
Disease Freedom (%)
60
40
20
0
0
12
24
36
48
60
72
84
Time (months)
References
1. Dickstein G, Shechner C, Arad E, Best L-A, Nativ O. 1998 Is there a role for low doses of mitotane (o,p’-DDD) as adjuvant therapy in adrenocortical car- cinoma? J Clin Endocrinol Metab. 83:3100-3103.
2. Schteingart DE, Motazedi A, Noonan RA, Thompson NW. 1982 Treatment of adrenal carcinoma. Arch Surg. 117:1142-1146.
3. Bodie B, Novick AC, Pontes JE, et al. 1989 The Cleveland Clinic experience with adrenal cortical carcinoma. J Urol. 141:257-260.
4. Luton JP, Cedars S, Billaud L, et al. 1990 Clinical features of adrenocortical carcinoma, prognostic factors and the effect of mitotane therapy. N Engl J Med. 322:1195-1201.
5. Vassilopoulou-Sellin R, Guinee VF, Klein MJ, et al. 1993 Impact of adjuvant mitotane on the clinical course of patients with adrenocortical cancer. Cancer. 71:3119-3123.
6. Haak HR, Hermans J, van de Velde CJR, et al. 1994 Optimal treatment of adrenocortical carcinoma with mitotane: results in a consecutive series of 96 patients. Br J Cancer. 69:947-951.
7. Kasperlik-Zaluska AA, Migdalska BM, Zgliczynski S, Makowska AM. 1995 Adrenocortical carcinoma. A clinical study and treatment results of 52 patients. Cancer. 75:2587-2591.
8. Barzon L, Fallo F, Sonino N, Daniele O, Boscaro M. 1997 Adrenocortical carcinoma: Experience in 45 patients. Oncology. 54:490-496.
Is There a Role for Low Doses of Mitotane (o,p’,DDD) as Adjuvant Therapy in Adrenocortical Carcinoma ?- Authors’ Responsed
To the editor:
We thank Drs. Barzon et al. for their letter (above) with regard to our above mentioned paper (1). This allows us to reemphasis the main point in our study, which was probably not clear enough. The most important issue we see in the adjuvant treatment with mitotane in adrenocortical carcinoma is the low dose of 1.5-2.0 g. This dose is well tolerated by our patients, who conduct normal life style, including vacations abroad. It is therefore not relevant to speak about “side-effects of mitotane, which significantly worsen quality of life of patients” with regard to our pa- tients. Barzon’s group used 4.0-8.0 g mitotane, which cannot be con- sidered a low dose and indeed causes severe side effects. Surprisingly
d Received January 11, 1999. Address correspondence to: Gabriel Dickstein, M.D., Division of Endocrinology, Bnai Zion Medical Center, Haila, 31048 Israel.
as it might seem, we think that the therapeutic effect of low doses might be better than that of high doses. This because of a much higher com- pliance in taking the low dose treatment regularly. Because of the severe side effects, we find it hard to believe that patients continue taking 8.0 g mitotane regularly for years and a treatment not taken regularly is probably less effective than one taken constantly, though in a lower dose. Even so, we tend to disagree with Barzon’s et al. conclusion of the ineffectiveness of treatment in their group. Although they show (in Fig. 1 of their letter) that recurrence of disease was not effected by high-dose mitotane treatment, survival rate was 73% (8 out of 11) in the treatment group and only 47% (7 out of 15) in the no-treatment group. How can these data not show a beneficial effect of treatment?
Since sending our paper, we have had two more patients with ad- renocortical carcinoma (17 cm, 1500 g, and 12 cm, 760 g) on the same mode of mitotane treatment for about one year now. All patients are doing well.
In conclusion, we agree that our patient group is small. We are sure that this mode of treatment will not prove to be 100% successful. How- ever, we are also sure that low-dose mitotane treatment in adrenocortical carcinoma is beneficial and well tolerated by patients, without signifi- cant side effects, and without any complications.
Gabriel Dickstein Bnai Zion Medical Center Haifa, 31048, Israel
References
1. Dickstein G, Shechner C, Arad E, Best L-A, Nativ O. 1998 Is there a role for low doses of mitotane (o,p’-DDD) as adjuvant therapy in adrenocortical car- cinoma? J Clin Endocrinol Metab. 83:3100-3103.
Uneventful Pregnancy in an Acromegalic Patient Treated with Slow-Release Lanreotide: A Case Reporte
To the editor:
Until recently, pregnancy was considered an unfrequent event in acromegalic females. With the advent of advanced surgical and medical management more affected women will probably get pregnant, as re- viewed in the recent paper by Herman-Bonert et al. (1). Now that so- matostatin analogues are the drugs of choice in acromegaly, the safety of their use in pregnancy is becoming of concern. We report the first case of an acromegalic patient who became pregnant while being treated with slow-release lanreotide.
The patient had developed oligomenhorrea and progressive enlarge- ment of the hands and feet since the age of 25, after a normal pregnancy. In 1995, when she was 29, she was investigated for suspected acromeg- aly. Mean basal GH was 28 ng/ml and decreased only to 18 ng/ml during oral glucose tolerance test; insulin-like growth factor (IGF)-I was 1099 ng/ml (normal reference values 150-269 ng/ml).
A pituitary nuclear magnetic resonance image disclosed an intrasellar adenoma 10 mm in diameter, and the patient underwent a selective adenomectomy by transphenoidal route. She was lost at follow-up until December 1996. On that occasion mean basal GH was 10 ng/ml and IGF-I 630 ng/ml, although a pituitary nuclear magnetic resonance im- age did not reveal any tumor mass. She referred normal menses, the last one on December 23. On December 30 she received slow-release lan- reotide, 30 mg i.m., and the same dose was given on January 13 and 27. Thereafter lanreotide was discontinued because she became pregnant. Pregnancy was uncomplicated for both the mother and the fetus, and a normal vaginal delivery took place on September 27. The Apgar score of the newborn was 9 and 10 at 1 and 10 min respectively: her weight was 2950 g, and her length was 49.5 cm. No malformations were ob- served, and postnatal development is normal.
Pregnancy is considered quite a rare event in acromegalic females because fertility is often reduced (1). Somatostatin analogues actually represent the medical treatment of choice for acromegaly. They may cause resumption of menses and ovulation in acromegalics by lowering
GH and IGF-I levels, by causing shrinkage of the tumor, and perhaps also due to an opiate antagonistic action (2), but this effect was not confirmed in humans (3). Apart from their influence on fertility, the safety of somatostatin analogues in pregnancy is of concern, for soma- tostatin receptors are expressed during fetal life (4). Toxicological studies have shown that octreotide and lanreotide do not cause malformations and have no significant effects on prenatal and postnatal development at conventional doses (5,6). Experience in humans is limited also because patients are advised to avoid pregnancy during treatment with soma- tostatin analogues. Octreotide passes the placenta, and its concentration in umbilical-cord serum was 359 ng/mL in a newborn whose mother was being treated for a TSH-secreting adenoma (7). To our knowledge, seven acromegalic patients received octreotide during their pregnancy (1, 8-11); in all but two cases octreotide was stopped early during pregnancy. All newborns showed no malformations and normal post- natal development.
Lanreotide is a synthetic somatostatin analogue, and a slow-release formulation proved effective in the treatment of acromegaly and may increase the compliance of patients (12). On the other hand, with the slow-release formulation, the fetus is exposed to the somatostatin an- alogue for a longer time, even after drug suppression because of pregnancy.
We report the first case of an acromegalic patient treated with slow- release lanreotide during pregnancy. The drug was discontinued as soon as the patient was found to be pregnant, but the embryo had been exposed to lanreotide for at least one month. The pregnancy was un- eventful; the fetal development was normal, the newborn in good health, and the postnatal growth regular.
In conclusion, despite quite reassuring preliminary reports, it seems safest to discontinue somatostatin analogues during pregnancy until more data are obtained. Furthermore many women in the fertile age should receive adequate contraception if treated with somatostatin an- alogues, as these drugs may induce resumption of menses and may improve fertility.
Ernesto de Menis, Domenico Billeci and Elisabetta Marton Ospedale Regionale Treviso 31100, Italy
Gualberto Gussoni Milano, 20156, Italy
References
1. Herman-Bonert V, Seliverstov M, Melmed S. 1998 Pregnancy in acromegaly: successful therapeutic outcome. J Clin Endocrinol Metab. 83:727-731.
2. Maurer R, Gaehwiler BH, Buescher HH, Hill RC, Roemer D. 1982 Opiate antagonistic properties of an octapeptide somatostatin analogue. Proc Natl Acad Sci USA. 79:4815-4817.
3. Del Pozo E, Lederman HJ, Gonon M, Sieber C. 1998 Effects of sandostatin on hormonal homeostasis: studies in normal subjects. In: Landolt AM, Heitz PU, Zapf J, Girard J, Del Pozo E, eds. Advances in the biosciences. Vol. 69. Advances in pituitary adenoma research. New York: Pergamon: 213-220.
4. Epelbaum J. 1997 Multiple somatostatin functions along brain development and aging. J Endocrinol Invest. 20 [Suppl]: 11.
5. Scarpignato C, Camboni MG. 1996 Safety profile of octreotide. In: Scarpignato C, ed. Octreotide: from basic science to clinical medicine. Prog Basic Clin Pharmacol. Karger: Basel; 10:296-309.
6. Chevrel B. 1995 Efficacité de la Somatuline LP 30 mg, analogue de la soma- tostatine à libération prolongee, dans le traitement des tumeurs carcinoides. Medicines & Chirurgie Digestive. 24:347-353.
7. Caron P, Gerbeau C, Pradayrol L. 1995 Maternal-fetal transfer of octreotide. N Engl J Med. 333:601-602.
8. Landolt AM, Schmid J, Wimpfheimer C, Karlsson E, Boerlin V. 1989 Suc- cessful pregnancy in a previously infertile woman treated with SMS 201-995 for acromegaly. N Engl J Med. 320:671-672.
9. Montini M, Pagani G, Gianola D, Pagani MD, Piolini R, Camboni MG. 1990 Acromegaly and primary amenorrhea: ovulation and pregnancy induced by SMS 201-995 and bromocriptine. J Endocrinol Invest. 13:193.
10. Colao A, Merola B, Ferone D, Lombardi G. 1997 Acromegaly. J Clin Endo- crinol Metab. 82:2777-2781.
11. Paiva I, Barros L, Gomes F, et al. Successful pregnancy in an acromegalic woman treated with octreotide. IV European Congress of Endocrinology, Sevilla, Spain, 1998. (Abstract P2-99).
12. Caron P, Morange-Ramos I, Cogne M, Jaquet P. 1997 Three-year follow-up of acromegalic patients treated with intramuscular slow-release lanreotide. J Clin Endocrinol Metab. 82:18-22.
e Received November 5, 1998. Address correspondence to: Ernesto De Menis, M.D., I Divisione Medica, Ospedale Regionale, 31100 Treviso, Italy.
Comment on “True” and “Apparent” Bone Density Measurement In Children with GH Deficiencyf
To the editor:
The data of Baroncelli and colleagues (1) reinforce the need to relate bone mass to bone volume in the growing skeleton. They have dem- onstrated that growth hormone deficiency separately reduces both the size of the bones and the amount of bone within the periosteal envelope, but this important conclusion is obscured by confusing terminology. “True” bone density refers to bone as a substance or material, whereas “apparent” bone density refers to a whole bone as an organ (2, 3). The phrase “apparent true bone density,” which appears several times in the text and in the editorial flyer on the cover, is an absurdity. Also, the accumulation of cancellous and cortical bone during growth should not be referred to as “mineralization,” which is the accumulation of mineral by osteoid. This process is unaffected by growth hormone deficiency, which causes not “undermineralization” but reduced net bone forma- tion on the endosteal envelope.
A. Michael Parfitt Division of Endocrinology and Metabolism University of Arkansas Medical School Little Rock, AR 72205
References
1. Baroncelli GI, Bertelloni S, Ceccarelli C, Saggese G. 1998 Measurement of volumetric bone mineral density accurately determines degree of lumbar un- dermineralization in children with growth hormone deficiency. J Clin Endo- crinol Metab. 83:3150-3154.
2. Robinson RA. 1960 Chemical analysis and electron microscopy of bone. In: Rodahl K, Nicholson JT, Brown EM, eds. Bone as a tissue. New York; McGraw- Hill Book Company, 186-250.
3. Parfitt AM. 1988 The composition, structure, and remodeling of bone: A basis for the interpretation of bone mineral measurements. In: Dequeker J, Geusens P, Wahner HW, eds. Bone mineral measurements by photon absorptiometry: Methodological problems. Leuven; Leuven University Press: 9-28.
Measurement of Volumetric Bone Mineral Density Accurately Determines Degree of Lumbar Undermineralization in Children with Growth Hormone Deficiency-Author’s Responses
To the editor:
We appreciate the comments of Dr. M. Parfitt about our recent study (1), and we agree with them. Our study shows that anthropometric variables and bone size affect lumbar bone mineral content (BMC) and bone mineral density (BMD), measured by dual energy x-ray absorp- tiometry (DEXA), in children with growth hormone (GH) deficiency. In order to reduce the influence of bone size on BMD measurement, math- ematical models to correct the BMD values on the basis of the estimated lumbar bone volume have been proposed (2-4). However, there is no doubt that BMDarea and BMDvolume are surrogate of the true bone den- sity. This is also evident in the terminology we and others use, e.g. “bone mineral apparent density” (3, 5), “apparent volumetric bone mineral density” (2), “volumetric bone mineral density” (6,7), “volumetric bone mineral apparent density” (8, 9), or “apparent true bone density” (1) to indicate the correction of BMC for bone volume. The term “apparent” reinforces that density is not a real or true density but a bone mineral mass within a region, not all of which is mineral (10). Thus, BMD, volume reflects only an estimation of true bone density, but it is not the true bone density. Indeed, as recently stated in an editorial by Seeman (11), the terms “apparent” and “real” are almost universally dropped from the literature for brevity and convenience, though at the price of under-
f Received December 2, 1998. Address correspondence to: Dr. A. Michael Parfitt, Division of Endocrinology and Metabolism, University of Arkansas Medical School, 4301 W. Markham Street, Slot 587, Little Rock, AR 72205-7199.
8 Received December 23, 1998. Address correspondence to: Giampi- ero I. Baroncelli, Endocrine Unit, Department of Pediatrics, University of Pisa, Via Roma 67, I-56125 Pisa, Italy.
standing that the size of the bone influences the reported measurement of bone density.
During growth, volumetric apparent BMD depends not only on the amount of cortical and trabecular bone contained within the periosteal surface of the bone and its true BMD, but also on the growth of the external size related to the accrual of bone taking place within the growing bone (11). Thus, in children with GH deficiency a reduced BMDvolume may reflect a decrease in mineral accrual or in bone size. Additionally, the reduced bone size did not completely account for the reduction in BMD area and BMD volume, suggesting that children with GH deficiency may have a reduced amount of bone within the periostial envelope (1). However, on the basis of the methodological problems related to the measurement of BMD by DEXA, in the conclusion of our article (1) we clearly stated that “further studies are needed to define whether true bone density is affected in children with GH deficiency.”
Although we agree with Dr. Parfitt that “mineralization” reflects the accumulation of mineral by osteoid, many authors employed the terms “bone mineralization” (12-15), “skeletal mineralization” (16), or “bone mineral status” (12, 15) to indicate the mass of mineral in a skeletal region (not all of which is bone) measured by noninvasive methods such as single- or dual-photon absorptiometry or DEXA, and expressed as BMD. Thus, in our article (1) the term “undermineralization” was used syn- onymously with reduced BMD corrected for the estimated bone volume (BMDvolume) in children with GH deficiency.
We thank Dr. Parfitt for giving us the opportunity to clarify some methodological problems related both to DEXA measurement in chil- dren and to the terminology usually employed to report the results obtained with this technique. In this regard, unanimous agreement on the terminology used to define “bone mineral” measured by DEXA would avoid confounding messages.
Giampiero I. Baroncelli, Silvano Bertelloni, Cinzia Ceccarelli, and Giuseppe Saggese Endocrine Unit, Department of Pediatrics University of Pisa I-56125 Pisa, Italy
References
1. Baroncelli GI, Bertelloni S, Ceccarelli C, Saggese G. 1998 Measurement of volumetric bone mineral density accurately determines degree of lumbar un- dermineralization in children with growth hormone deficiency. J Clin Endo- crinol Metab. 83:3150-3154.
2. Kroger H, Kotaniemi A, Vainio P, Alhava E. 1992 Bone densitometry of the spine and femur in children by dual-energy x-ray absorptiometry. Bone Miner. 17:75-85.
3. Carter DR, Bouxsein ML, Marcus R. 1992 New approaches for interpreting projected bone densitometry data. J Bone Miner Res. 7:137-145.
4. Peel NFA, Eastell R. 1994 Diagnostic value of estimated volumetric bone mineral density of the lumbar spine in osteoporosis. J Bone Miner Res. 9:317-320.
5. Katzman DK, Bachrach LK, Carter DR, Marcus R. 1991 Clinical and anthro- pometric correlates of bone mineral acquisition in healthy adolescent girls. J Clin Endocrinol Metab. 73:1332-1339.
6. Lu PW, Cowell CT, Lloyd-Jones SA, Briody JN, Howman-Giles R. 1996 Volumetric bone mineral density in normal subjects, aged 5-27 years. J Clin Endocrinol Metab. 81:1586-1590.
7. Boot AM, De Ridder MAJ, Pols HAP, Krenning EP, De Muinck Keizer- Schrama SMPF. 1997 Bone mineral density in children and adolescents: re- lation to puberty, calcium intake, and physical activity. J Clin Endocrinol Metab. 82:57-62.
8. Tabensky AD, Williams J, Deluca V, Briganti E, Seeman E. 1996 Bone mass, areal, and volumetric bone density are equally accurate, sensitive, and specific surrogates of the breaking strength of the vertebral body: an in vitro study. J Bone Miner Res. 11:1981-1988.
9. Ferrari S, Rizzoli R, Slosman D, Bonjour J-P. 1998 Familial resemblance for bone mineral mass is expressed before puberty. J Clin Endocrinol Metab. 83:358-361.
10. Seeman E. 1997 From density to structure: growing up and growing old on the surfaces of bone. J Bone Miner Res. 12:509-521.
11. Seeman E. 1998 Growth in bone mass and size. Are racial and gender differ- ences in bone mineral density more apparent than real? J Clin Endocrinol Metab. 83:1414-1419.
12. Southard RN, Morris JD, Mahan JD, et al. 1991 Bone mass in healthy children: measurement with quantitative DXA. Radiology. 179:735-738.
13. Shaw NJ, Bishop NJ. 1995 Mineral accretion in growing bone: a framework for the future? Arch Dis Child. 72:177-179.
14. Molgaard C, Thomsen BL, Prentice A, Cole TJ, Michaelsen KF. 1997 Whole
body bone mineral content in healthy children and adolescents. Arch Dis Child. 76:9-15.
15. Shore RM, Poznanski AK. 1996 Radiologic evaluation of bone mineral in children. In: Favus MJ, ed. Primer on the metabolic bone diseases and disorders of mineral metabolism. 3rd ed., New York: Lippincott-Raven; 119-134.
16. Slemenda CW, Reister TK, Hui SL, Miller JZ, Christian JC, Johnston CC. 1994 Influences on skeletal mineralization in children and adolescents: evi- dence for varying effects of sexual maturation and physical activity. J Pediatr. 125:201-207.
Comment on Carney Complex and Related Syndromes and their Genetic Locih
To the editor:
In a recent article Stratakis et al. (1) tested the hypotheses in two multitumoral syndromes showing genetic heterogeneity, such as Carney Complex (CC) and Peutz-Jeghers-Syndrome (PJS), that some families with CC may map to the genetic loci of these conditions (locus 2p16 and 19p13.3 or 19q13.4, respectively), and that loss of heterozygosity (LOH) for PJS and Cowden disease (PTEN gene mapped at 10q22-23) loci were involved in the molecular pathology of CC tumors. The first suggested explanation was the following. “Because the STK11/KKB1 and PTEN genes appear to function as tumor suppressor genes, it is possible that the products of these genes are members of a family of proteins that regulate the same cellular process.” Stratakis et al. report as examples of clinical and genetic overlap the Muir-Torre syndrome and HNPCC or MEN2 and Hirschsprung disease. However, the two non-2p-linked CC families analyzed in the study by Stratakis et al. (not mapping at 2p16) did not map to the 19p13, 19q13.4, and 10q23 loci either, and tumors from patients with CC did not show LOH for these loci. The authors conclude that “the PJS and the PTEN genes may not play a significant role in the molecular pathogenesis of tumors associated with CC, despite the clin- ical and histological similarities between these disorders.” Because the PJS locus was identified by screening only DNA of colonic polyps, the authors suggest that, “It is possible… that LOH for the PJS genomic region is necessary for oncogenesis in the colon but not in other organs affected by PJS or CC. According to Knudson’s hypothesis… , LOH is necessary for oncogenesis in the presence of a recessive mutant allele, whereas a dominant mutant allele is sufficient for tumorigenesis. If tissue-specific conditions were to determine the dominant or recessive function of the mutant PJS allele, a variable pattern of LOH for the PJS locus would be observed in the various tissues from patients with the syndrome.”
Here, we report a similar experience with another multitumoral syn- drome, namely familial adenomatous polyposis (FAP), concerning an extracolonic manifestation of endocrinologic interest, such as thyroid carcinoma. Thyroid carcinoma of the papillary histotype is a tumor integral to the FAP syndrome (2), determined by germ-line mutations of the APC gene, mapped at 5q21 (3). LOH of the APC gene is common in patients with colonic polyps or cancer, desmoids or hepatoblastomas belonging to the FAP syndrome (4). However, we found no LOH for APC in the thyroid tumoral tissue of five patients with FAP associated papillary carcinoma (5). Four of them had an APC germ-line mutation at codon 1061 (6). The last one had mutation at codon 1309. It is note- worthy that three of them belonged to the same kindred (7). Interest- ingly, three of the four had activation of the chimeric RET-PTC, as RET-PTC1, deriving from the fusion of the RET gene with another gene named H4 (8). This observation is consistent with the lack of mutations of the tumor suppressor gene APC in sporadic thyroid tumors (9, 10). Even if other factors are required for the expression of the tumoral phenotype in the thyroid tissue, such as sex-related factors (female to male ratio: 20:1) or environmental factors, namely radiation in the atmosphere (11), according to the hypothesis suggested by Stratakis et al. (1), our findings could simply suggest that APC gene acted as a dominant gene, and the dominant or recessive function of the mutant allele of a tumor suppressor gene, such as APC, could be determined by tissue specific conditions, varying from one tissue to another in the same patient. For instance, in our patients, the germ-line APC mutation co- operated with the ki-ras oncogene, according to the Vogelstein and
Fearon model of tumorigenesis (12) to determine colonic polyps and cancer, and with ret-PTC, which is mutually exclusive with ki-ras in thyroid tumorigenesis, to determine papillary thyroid carcinoma (13).
Francesco Cetta Institute of Surgical Clinics University of Siena 53100 Siena, Italy
References
1. Stratakis CA, Kirschner LS, Taymans SE, et al. 1998 Carney complex, Peutz- Jeghers syndrome, Cowden disease, and Bannayan-Zonana syndrome share cutaneous manifestations, but not genetic loci. J Clin Endocrinol Metab. 83:2972-2976.
2. Harach HR, Williams GT, Williams ED. 1994 Familial adenomatous polyposis associated thyroid carcinoma: A distinct type of follicular cell neoplasm. His- topathology. 25:549-561.
3. Groden J, Thliveris A, Samowitz W, et al. 1991 Identification and character- ization of the familial adenomatous polyposis coli gene. Cell. 66:589-600.
4. Palmirotta R, Curia MC, Esposito DL, et al. 1995 Novel mutations and in- activation of both alleles of the APC gene in desmoid tumors. Hum Mutat. 10:1979-1981.
5. Cetta F, Montalto G., Petracci M., et al. 1998 The wild type APC allele is not lost in FAP associated thyroid tumors, showing activation of the chimeric oncogene ret-PTC. Gastroenterology 114:A1221.
6. Cetta F, Toti P, Petracci M, et al. 1997 Thyroid carcinoma associated with familial adenomatous polyposis. Histopathology 31:231-236.
7. Civitelli S, Tanzini G, Cetta F, Petracci M, Pacchiarotti MC, Civitelli B. 1996 Papillary thyroid carcinoma in three siblings with familial adenomatous pol- yposis. Int J Colorect Dis. 11:571-574.
8. Cetta F, Chiappetta G, Melillo RM, et al .: 1997 The ret-PTC1 oncogene is activated in familial adenomatous polyposis associated with thyroid papillary carcinomas. J Clin Endocrinol Metab. 83:1003-1006.
9. Colletta G, Sciacchitano S, Palmirotta R, et al .: 1994 Analysis of adenomatous polyposis coli gene in thyroid tumors. Br J Cancer. 70:1085-1088.
10. Zeki K, Spambalg D, Sharifi N, Gonsky R, Fagin JA. 1994 Mutations of the adenomatous polyposis coli gene in sporadic thyroid neoplasms. J Clin En- docrinol Metab. 79:1317-1321.
11. Cetta F, Montalto G, Petracci M, Fusco A. 1997 Thyroid cancer and the Chernobyl accident. Are long-term and long-distance side effects of fall-out radiation greater than estimated? J Clin Endocrinol Metab. 82:2015-2017.
12. Kinzler KW, Vogelstein B. 1996 Lesson from hereditary colorectal cancer. Cell. 87:159-170.
13. Cetta F, Olschwang S, Petracci M, et al. 1998 Genetic alterations in thyroid carcinoma associated with familial adenomatous polyposis. Clinical implica- tions and suggestions for early detection. World J Surg. 22:1231-1236.
Carney Complex and Related Syndromes and their Genetic Loci-Author’s Response2
To the editor:
The data presented by Cetta et al. support our hypothesis that tissue- specific conditions may determine the need for loss-of-heterozygosity (LOH) of tumor-suppressor genes in the process of oncogenesis (1). Mech- anisms that may make LOH unnecessary include inactivating mutations of the normal allele and other genomic rearrangements [which would not be identifiable by simple polymerase chain reaction (PCR)-allelotyping] and tissue-specific imprinting, which has recently been demonstrated to occur in such genes as Gsa, IGF-II, and KVLQT-1 (2-4). In addition, the classic separation between oncogenes and tumor-suppressor genes may not apply in complex pathways leading to oncogenesis (5). Finally, as we pointed out and Cetta et al. underlined, a particular mutation in a tumor-suppressor gene may act in a dominant manner. This is certainly true for dominant negative effects (6) and, perhaps, for the presence of modifier genes, whose expression is tissue-dependent.
Thus, we agree with Cetta et al. that their (and, perhaps, our) findings support this hypothesis. However, one should be cautious in interpret- ing LOH data from various tissues. Normal cells are almost always there to “contaminate” tumor DNA, unless methods such as laser-guided
i Received January 8, 1999. Address correspondence to: Constantine A. Stratakis, M.D., D.Sc., Head, Unit on Genetics & Endocrinology (UGEN), Developmental Endocrinology Branch, National Institute on Child Health and Human Development, National Institutes of Health, Building 10, Room 10N262, 10 Center Drive, MSC-1862, Bethesda, Mary- land 20892-1862.
h Received December 16, 1998. Address correspondence to: Francesco Cetta, Institute of Surgical Clinics, University of Siena, Nuovo Poli- clinico, Viale Bracci, 53100 Siena, Italy.
microdissection and single-cell PCR have been used. This is particularly important for lesions in which only a small proportion of tumor cells may demonstrate LOH. With this caveat in mind, we thank Dr. Cetta and his coworkers for supporting our hypothesis; clearly more work needs to be done in the clarification of the processes of endocrine oncogenesis.
Constantine A. Stratakis Head, Unit on Genetics & Endocrinology (UGEN) Developmental Endocrinology Branch, NICHD, NIH Bethesda, Maryland 20892
References
1. Stratakis CA, Kirschner LS, Taymans SE, et al. 1998 Carney complex, Peutz- Jeghers syndrome, Cowden disease, and Bannayan-Zonana syndrome share
cutaneous and endocrine manifestations, but not genetic loci. J Clin Endocrinol Metab. 83:2972-2976.
2. Yu S, Yu D, Lee E, et al. 1998 Variable and tissue-specific hormone resistance in heterotrimeric Gs protein alpha-subunit (Gsa) knockout mice is due to tissue-specific imprinting of the gsalpha gene. Proc Natl Acad Sci USA. 95:8715-8720.
3. Wu HK, Squire JA, Song Q, Weksberg R. 1997 Promoter-dependent tissue- specific expressive nature of imprinting gene, insulin-like growth factor II, in human tissues. Biochem Biophys Res Commun. 233:221-226.
4. Lee MP, Hu RJ, Johnson LA, Feinberg AP. 1997 Human KVLQT1 gene shows tissue-specific imprinting and encompasses Beckwith-Wiedemann syndrome chromosomal rearrangements. Nat Genet. 15:181-185.
5. He TC, Sparks AB, Rago C, et al. 1998 Identification of c-MYC as a target of the APC pathway. Science. 281:1509-1512.
6. Brachmann RK, Vidal M, Boeke JD. 1996 Dominant-negative p53 mutations selected in yeast hit cancer hot spots. Proc Natl Acad Sci USA. 93:4091-4095.
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