Discontinuation of Growth Hormone (GH) Treatment: Metabolic Effects ...

0021-972X/99/$03.00/0 The Journal of Clinical Endocrinology & Metabolism Copyright © 1999 by The Endocrine Society

Vol. 84, No. 12 Printed in U.S.A.

Discontinuation of Growth Hormone (GH) Treatment: Metabolic Effects in GH-Deficient and GH-Sufficient Adolescent Patients Compared with Control Subjects* GUDMUNDUR JOHANNSSON, KERSTIN ALBERTSSON-WIKLAND, ON BEHALF OF THE SWEDISH STUDY GROUP FOR GROWTH HORMONE TREATMENT IN CHILDREN,† AND BENGT-ÅKE BENGTSSON Research Center for Endocrinology and Metabolism (G.J., B.-Å.) and Pediatric Growth Research Center (K.A.-W.), Sahlgrenska University Hospital, SE-413– 45 Goteborg, Sweden ABSTRACT The need for continuing GH replacement in patients with childhood-onset GH deficiency continuing into adulthood has been recognized. The metabolic consequences of discontinuing GH in adolescent patients with childhood-onset GH deficiency and short stature were examined over a period of 2 yr. Forty adolescents (aged 16 –21 yr) receiving GH treatment for more than 3 yr and 16 closely matched healthy controls were studied. After a baseline visit, GH treatment was discontinued. The patients were then examined with the same protocol once a year for 2 yr. Twenty-one patients had severe GH deficiency (GHD) into adulthood, whereas 19 patients were regarded as having sufficient endogenous GH secretion (GHS). After 2 yr without GH treatment, the serum insulin-like growth factor I level was

A

DULTS RECEIVING hormone replacement therapy due to hypopituitarism but with untreated GH deficiency (GHD) have been found to have increased body fat with abdominal/visceral obesity (1) and reduced lean body mass and bone mineral content (2, 3). Other common metabolic abnormalities include insulin resistance and dyslipoproteinemia with high low density lipoprotein (LDL) cholesterol (C), high serum triglycerides, and low high density lipoprotein (HDL) C concentrations (4, 5). An increased prevalence of hypertension (4), premature atherosclerosis (6), and increased mortality from cardiovascular disease (7) is also found in hypopituitary adults with untreated severe GHD. It has been suggested that the expression of GHD may differ between subjects with childhood-onset and adultonset disease. One study found that patients with childhoodonset GHD had a lower body mass index, lower waist to hip ratio, lower serum insulin-like growth factor I (IGF-I) con-

Received February 3, 1999. Revision received May 6, 1999. Accepted July 7, 1999. Address all correspondence and requests for reprints to: Gudmundur Johannsson, M.D., Ph.D., Research Center for Endocrinology and Metabolism, Sahlgrenska University Hospital, SE-413 45 Goteborg, Sweden. E-mail: [email protected]. * This work was supported by grants from the Swedish Medical Research Council (Project 11621). † Participants in the Swedish Study Group for Growth Hormone Treatment in Children: Kerstin Albertsson-Wikland, Jan Alm, Stefan Aronson, Jan Gustafsson, Lars Hagena¨s, Anders Ha¨ger, Sten Ivarsson, Berit Kristro¨m, Claude Marcus, Christian Moe¨ll, Karl-Olof Nilsson, Martin Ritzeń, Torsten Tuvemo, Ulf Westgren, Otto Westphal, and Jan Åman.

lower in GHD than in both GHS and control subjects. Both before and 2 yr after GH treatment was discontinued, serum concentrations of total cholesterol (C), low density lipoprotein C, and apolipoprotein B were higher in the GHD than in both GHS and control subjects. Serum concentrations of high density lipoprotein C decreased in the GHD group and increased in the other 2 study groups. The amount of total body and abdominal fat mass throughout the study and the increment in these masses were more marked in the GHD than in the GHS and control subjects when GH treatment was discontinued. The discontinuation of GH therapy in adolescents with severe GHD continuing into adulthood results over a period of 2 yr in the accumulation of important cardiovascular risk factors that are associated with GHD in adults. (J Clin Endocrinol Metab 84: 4516 – 4524, 1999)

centrations, and higher serum HDL-C concentrations as well as superior scores for quality of life compared with patients with adult-onset GHD (8). More severe consequences of GHD in terms of muscle mass (9) and bone mass (2) have also been suggested in adults with childhood-onset disease than in those with adult-onset disease. This may be an effect of the immediate discontinuation of GH treatment after final height is reached and before peak bone mass and maturation of other tissues have been achieved. Three small scale trials have studied the consequences of discontinuing GH treatment in adolescents after final height was achieved. The first study demonstrated a reduction in quadriceps muscle strength, muscle size, and muscle fiber area and an increase in the amount of body fat after 12 months without GH treatment in 8 adolescent patients (10). A second study followed 16 adolescent males for 12 weeks after the discontinuation of GH treatment (11). After 12 weeks, the fat mass had increased in the 6 patients with severe GHD, but not in the 10 subjects classified as having normal somatotropic function. A similar finding was reported in 8 adolescents followed for 12 months after GH treatment was stopped (12). More longitudinal data are needed to establish the long term consequences of GH discontinuation in childhoodonset GHD. The aim of the present study was, therefore, prospectively to follow the consequences of discontinuing GH therapy in adolescents with GHD of childhood onset and short stature. All of the subjects had been receiving long term GH replacement in childhood and were treated for a significant period of time after final height was reached.

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DISCONTINUING GH TREATMENT IN ADOLESCENTS Subjects and Methods Patients and controls Forty adolescent patients receiving GH treatment within clinical trials and 16 healthy control subjects were recruited for the study. The GHtreated subjects were submitted for participation from 14 pediatric clinics. The criteria for inclusion were GHD, idiopathic or organic, and isolated or multiple anterior pituitary hormone deficiencies. The patients had received GH treatment for the past 3 consecutive yr and were otherwise being considered to end GH treatment. Patients who were not considered for inclusion were those who planned to finalize treatment for reasons other than reaching final height, those older than 25 yr at the time of inclusion, pharmacological treatment for psychiatric disease, or mental retardation. Subjects were partly selected for the study so as to have approximately half the subjects with childhood-onset, idiopathic, isolated GHD and half with organic hypothalamic-pituitary disease with or without multiple pituitary hormone deficiencies. The mean age of the adolescents receiving GH treatment who were included was 19 yr, with a range of 16 –21 yr. The average height sd score was 22.5 6 0.31 when GH treatment was initiated in childhood and 20.67 6 0.19 when patients were included in the present study. Most subjects had idiopathic and isolated GHD, and 12 subjects had organic hypothalamic/pituitary disease (Table 1). All patients with brain neoplasia and acute lymphoblastic leukemia had received irradiation in the hypothalamic-pituitary area. Patients with other anterior pituitary hormone deficiencies received, when required, stable replacement therapy with glucocorticoids (cortisone acetate; mean, 20 mg; range, 15–30 mg/ day), thyroid hormone (levothyroxine; mean, 0.1 mg; range, 0.05– 0.15 mg/day), and gonadal steroids. Healthy control subjects were recruited. They were selected from subjects who responded to an advertisement. They were selected to closely match the patient group in terms of age, sex, body height, and body weight. Sixteen healthy control subjects were enrolled in the study. They underwent similar physical and laboratory examinations as the patients on two occasions with 2 yr in between.

Study protocol During a stabilizing period of 3 months, all patients received a standardized GH dose of 0.03 mg/kgzday (0.1 IU/kgzday). After a baseline visit, at which all the physical, laboratory, and body composition examinations were performed, GH treatment was discontinued. The patients were then examined with the same protocol once a year for 2 yr. Between each annual visit, the patients were seen at the home pediatric clinic, where their clinical status was assessed. One year after GH treatment was stopped, a 24-h GH profile was performed to assess endogenous GH secretion. Six patients with suspected isolated GHD according to low endogenous GH secretion also underwent an insulin tolerance test after the 2-yr follow-up period. Body

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weight was measured in the morning to the nearest 0.1 kg with the subject wearing indoor clothing, and body height was measured barefoot to the nearest 0.01 m. The body mass index (BMI) was calculated as body weight in kilograms divided by height in meters squared. Systolic and diastolic blood pressures were measured after 5 min of supine rest using the sphygmanometric cuff method.

Methods Blood samples were drawn in the morning after an overnight fast. The serum concentration of IGF-I was determined by a hydrochloric acidethanol extraction RIA using authentic IGF-I for labeling (Nichols Institute Diagnostics, San Juan Capistrano, CA) with within-assay coefficients of variation (CV) of 2.5% and 4.2% at serum concentrations of 125 and 345 mg/L, respectively. The IGF-binding protein-3 (IGFBP-3) concentration in serum was determined by RIA (Nichols Institute Diagnostics), with total CVs of 6.2% and 5.7% at serum concentrations of 2.05 and 3.49 mg/L, respectively. The GH secretory status was assessed by 24-h GH measurements from repeated 30-min blood sampling using a withdrawal pump. Serum GH was determined by a polyclonal antibody-based immunoradiometric assay (Pharmacia Biotech, Uppsala, Sweden) using IRP 80/505 as standard. The detection limit of the assay was 0.1 mg/L, and the total CV was 5.3% for a serum pool of 6.6 mg/L. The GH area under the curve, the mean 24-h GH concentration, and the GH maximum peak concentration from the 24-h GH measurements were calculated using the Pulsar program. Free T4 was determined by a luminometric labeled antibody immunoassay (MAB Free T4, Kodak Clinical Diagnostics Ltd., Amersham Pharmacia Biotech, Aylesbury, UK), and free T3 was analyzed by a ligand analog RIA (Amerlex M, Kodak Clinical Diagnostics). Serum insulin was determined by RIA (Phadebas, Pharmacia Biotech), and blood glucose was measured using the glucose-6-phosphate dehydrogenase method (Kebo Lab, Stockholm, Sweden). Hemoglobin A1c was determined by high pressure liquid chromatography (Waters Corp., Massachusetts). Serum total cholesterol (TC) and triglyceride concentrations were determined with fully enzymatic methods (Roche Molecular Biochemicals, Mannheim, Germany). The within-assay CVs for TC and triglyceride determinations were 0.9% and 1.1%, respectively. Apolipoprotein (apo) B concentrations were determined with an immunoturbidometric assay (UniKit Roche, Hoffman-LaRoche Inc., Nutley, NJ) with a withinassay CV of 1.9%. HDL-C was determined after the precipitation of apo B-containing lipoproteins with MgCl2 and heparin. The LDL-C concentration was calculated according to Friedewald’s formula adjusted to Systeme International units. The lipoprotein(a) [Lp(a)] concentration was determined with a RIA (Pharmacia Biotech). This Lp(a) assay was standardized against an electroimmunoassay. The within-assay CV for the Lp(a) assay was 4.4%.

TABLE 1. Characteristics of the 40 adolescent subjects discontinuing GH treatment after final height was reached and 16 control subjects Variable

All patients

GH-deficient

GH-sufficient

Gender (men/women) Age (yr) Age at GH start (yr) Body height (m) Mean 24-h GH conc. (mg/L) Max. 24-h GH conc. (mg/L) Cause of pituitary deficiency Idiopathic Acute lymphoblastic leukemia Brain tumor Other Degree of pituitary deficiency after reevaluation Adrenal Thyroid Gonadal Isolated GHD

31/9 19 (16 –21) 11 (2–16) 1.72 (1.54 –1.85) 0.9 (0.0 –3.3) 7.8 (0.0 –32.6)

17/4 19 (16 –21) 11 (6 –15) 1.74 (1.61–1.83) 0.2 (0.0 – 0.8) 1.2 (0.0 –3.3)

15/4 19 (17–21) 12 (2–16) 1.70 (1.54 –1.85) 1.6 (0.4 –3.3) 14.4 (3.3–32.6)

Control

12/4 19 (17–22) 1.73 (1.59 –1.83) 1.8 (0.2– 4.5) 12.3 (1.8 –33.0)

28 3 5 4 7 13 10 5

Values are means, with ranges in parentheses. The definitions of GH deficiency and GH sufficiency are given in Results under the heading 24-h GH secretion and classification of subjects.

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TABLE 2. Biochemical measurements in 40 adolescent subjects discontinuing GH treatment at final height and 16 healthy controls Variable

IGF-I (mg/L) GH-deficient GH-sufficient Controls IGFBP-3 (mg/L) GH-deficient GH-sufficient Controls B-glucose (mmol/L) GH-deficient GH-sufficient Controls HbA1c (%) GH-deficient GH-sufficient Controls Insulin (mIU/L) GH-deficient GH-sufficient Controls SHBG (g/L) GH-deficient GH-sufficient Controls Systolic blood pressure (mmHg) GH-deficient GH-sufficient Controls Diastolic blood pressure (mmHg) GH-deficient GH-sufficient Controls

Baseline

1 yr

2 yr

P value

532 6 49a 766 6 75d 374 6 26

190 6 31 409 6 29 ND

195 6 28a,b,c 423 6 23c,d 326 6 27

,0.001 ,0.001 0.005

3.53 6 0.24 3.82 6 0.28 3.42 6 0.18

2.60 6 0.21 3.45 6 0.10 ND

2.67 6 0.22a,b,c 3.68 6 0.11 3.45 6 0.21

,0.001 0.2 0.9

3.9 6 0.1 4.2 6 0.1 4.1 6 0.1

3.8 6 0.1 4.0 6 0.1 ND

3.7 6 0.1 4.1 6 0.1 4.1 6 0.1

0.4 0.1 0.5

4.7 6 0.1 5.1 6 0.2 4.5 6 0.1

4.5 6 0.1 4.7 6 0.1 ND

4.4 6 0.1 4.5 6 0.1c 4.5 6 0.1

0.02 0.02 0.3

12.2 6 1.3 16.3 6 3.1 9.4 6 0.9

8.1 6 1.9 9.4 6 1.1 ND

7.5 6 1.3 10.4 6 1.3 8.3 6 0.9

0.008 ,0.001 0.4

22.9 6 3.2 32.3 6 9.1 41.9 6 12.3

25.3 6 5.1 24.4 6 3.1 ND

31.7 6 7.6b 25.9 6 4.0 48.9 6 15.6

0.08 0.4 0.2

115 6 3 118 6 2 114 6 3

112 6 3 110 6 2 ND

113 6 3 112 6 2 114 6 7

0.3 0.01 0.9

69 6 2 72 6 2 69 6 2

67 6 2 68 6 2 ND

73 6 2 71 6 2 72 6 2

0.007 0.4 0.2

Values are the mean 6 SEM; and the P value is derived from the within-group one-way ANOVA. ND, Not determined. a P , 0.05 vs. GHS and controls. b P , 0.05 vs. differences between 2 yr and baseline in GHS. c P , 0.05 vs. differences between 2 yr and baseline in controls. d P , 0.05 vs. controls. Body composition was determined using bioelectrical impedance analysis (BIA) and dual energy x-ray absorptiometry (DXA). DXA was performed using a whole body scanner (Lunar DPX-L, Lunar Corp., Madison, WI). Total body fat (BF) and lean body mass (LBM) were analyzed using the 1.31 software version. Precision errors (1 sd) on the scanner used (system number 7156), as determined from double examinations of 10 healthy subjects, were 1.7% for BF and 0.7% for LBM. The results are presented as the percentages of BF and LBM of body weight (BF% and LBM%). DXA can be used to estimate fat in specific anatomical regions (13), and in this study an abdominal region (trunk) was defined to assess abdominal fat mass. BIA was measured in the supine position (BIA-101 equipment, RJL System, Inc., Detroit, MI). The resistance was measured using a 50-kHz, 800-mamp and principally reflects the extracellular fluid volume (14). The BIA measurements had a day to day CV of 1.7%.

Ethics Informed consent was obtained from all patients. The study was approved by the ethics committee at the University of Goteborg.

Statistical analysis All descriptive statistical results are presented as the mean 6 sem. The overall within-group effect of discontinuing GH treatment was analyzed using a one-way ANOVA for repeated measurements. Student’s t test was used to analyze the differences between baseline and 2 yr between groups of subjects. Correlations were sought by calculating Pearson’s linear correlation coefficient. Because of the highly skewed distribution of the serum concentration of Lp(a), the descriptive results of Lp(a) are presented as the median and 25th and 75th percentiles, and a logarithmic

transformation of the Lp(a) concentration was used before other statistical analyses. Significance was obtained if two-tailed P # 0.05.

Results

Four subjects were not followed for 2 yr. One man with idiopathic, isolated GHD during childhood was not interested in further investigations after the baseline visit. Two women and one man, all with severe GHD, withdrew from the study after 3, 6, and 12 months, respectively, as a result of severe psychological symptoms, which were resolved after the reinstitution of GH replacement therapy. These subjects are not included in the longitudinal data analysis. 24-h GH secretion and classification of subjects

Severe GHD into adulthood was defined as: 1) another anterior pituitary hormone deficiency associated with a spontaneous GH peak of less than 3 mg/L (17 subjects); 2) an organic hypothalamic/pituitary disease associated with a GH peak of less than 3 mg/L during an insulin tolerance test (3 subjects); and 3) in the absence of an organic hypothalamic/pituitary disease, a GH peak of less than 3 mg/L during 2 GH stimulation tests (1 subject). Using these criteria, 21 patients were classified as having severe GHD into adulthood, whereas 19 patients were clas-

DISCONTINUING GH TREATMENT IN ADOLESCENTS

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sified as GH sufficient (GHS). These 2 patient groups were similar in terms of age, body height, the proportions of men and women, and age at the start of GH treatment in childhood (Table 1). The period of GH treatment was longer in the GHD group (9 yr; range, 4 –15 yr) than in the GHS group (7 yr; range, 3–16 yr; P 5 0.03), and the prospective evaluation of age at onset of puberty was somewhat lower in the GHD group (13 vs. 14 yr; P 5 0.04). The average daily doses of GH during the past 2 yr before entering the study were 0.03 6 0.004 and 0.04 6 0.004 mg/kgzday in the GHD and GHS groups, respectively (P 5 0.2). In the GHD group, 5 patients had 1 additional anterior pituitary hormone deficiency, and 12 patients 2–3 additional anterior pituitary hormone deficiencies; 4 had isolated GHD. The GHS patients did not differ from the healthy control subjects in terms of 24-h mean GH secretion and 24-h maximum GH secretion. The GHD subjects had, however, markedly lower GH secretion than both the GHS group and the healthy controls (Table 1). Serum IGF-I and IGFBP-3

Before discontinuing GH treatment, serum IGF-I concentrations were markedly higher in both patient groups than in the healthy matched controls (Table 2 and Fig. 1). Serum IGF-I concentrations decreased in all groups during the 2-yr observation period. In the adolescents with severe GHD, the reduction in serum IGF-I was more marked than in the GHS group and the controls. At 2 yr, the serum IGF-I level was, therefore, lower in the GHD group than in both GHS patients and controls. In subjects with sufficient GH secretion, the baseline serum IGF-I concentration was higher than in the GHD patients and was higher than in both the GHD group and the controls after 2 yr without GH treatment. The reduction in serum IGF-I was positively correlated with the mean 24-h endogenous GH secretion (P 5 0.57 and P 5 0.001), demonstrating the largest reduction in serum IGF-I concentration in subjects with the lowest endogenous GH reserve. In contrast to serum IGF-I concentrations, IGFBP-3 concentrations were similar in all groups before GH treatment was discontinued (Table 2). During the 2 yr without treatment, serum levels of IGFBP-3 only decreased in the GHD group. At 2 yr, the levels of serum IGFBP-3 were therefore lower in the GHD group than in both the GHS and control groups. Glucose metabolism, blood pressure, and lipoproteins

Blood glucose levels did not change in the patients taken off GH treatment or in the controls during the 2 yr of observation. The level of hemoglobin A1c and serum insulin concentration decreased in both patient groups, whereas no changes were seen in the control group (Table 2). No changes occurred in the serum concentrations of free T4 and free T3. Systolic blood pressure only decreased in the GHS group in response to the discontinuation of GH treatment. In the GHD group, diastolic blood pressure demonstrated a transient reduction 1 yr after GH treatment was stopped, whereas after 2 yr of observation, diastolic blood pressure had increased (Table 2).

FIG. 1. A, Serum IGF-I concentrations before and 12 and 24 months after the discontinuation of GH treatment in adolescents. One group comprised 21 adolescents with severe GHD continuing into adulthood (solid line), the second group comprised 19 adolescents with their own GH secretion (GHS; broken line), and the third group consisted of 16 healthy controls studied on 2 occasions with 2 yr in between. B, Percent change in serum IGF-I concentrations between baseline and 2 yr after discontinuing GH treatment in the 2 patient groups and the controls. *, P , 0.05 compared with controls; †, P , 0.05 compared with the GHS group.

Before GH treatment was stopped, serum concentrations of total C, LDL-C, and apo B were higher in the GHD group than in both the GHS group and the control subjects (Table 3 and Fig. 2). After the discontinuation of GH treatment, the serum levels of these lipids increased in both patient groups, but not in the controls. The changes in serum levels of total C, LDL-C, and apo B did not, however, differ among the three groups during the 2-yr period of observation. After 2 yr, the serum levels were therefore still higher in the GHD group than in the GHS and control subjects. Serum concentrations of HDL-C increased in the healthy controls, and the change noted in the GHS group was in the same direction (Table 3). The slight reduction in HDL-C observed in the GHD group therefore resulted in a significantly different overall change in this group of patients compared with levels in both the GHS and control groups (Fig. 3). In the GHD group, serum triglyceride levels were higher than those in controls at baseline and then decreased in

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TABLE 3. Lipoprotein measurements in 40 adolescent subjects discontinuing GH treatment at final height and 16 healthy controls Variable

Total cholesterol (mmol/L) GH-deficient GH-sufficient Controls HDL cholesterol (mmol/L) GH-deficient GH-sufficient Controls LDL cholesterol (mmol/L) GH-deficient GH-sufficient Controls Triglycerides (mmol/L) GH-deficient GH-sufficient Controls Apolipoprotein B (mmol/L) GH-deficient GH-sufficient Controls Lp(a) (mmol/L) GH-deficient GH-sufficient Controls

Baseline

1 yr

2 yr

P value

4.91 6 0.20a 4.10 6 0.18 4.01 6 0.21

4.74 6 0.21 3.94 6 0.21 ND

5.24 6 0.24a 4.44 6 0.23 4.27 6 0.18

0.009 0.001 0.08

1.15 6 0.07 1.16 6 0.04 1.17 6 0.07

1.06 6 0.08 1.13 6 0.04 ND

1.09 6 0.09b,c 1.20 6 0.04 1.29 6 0.07

0.2 0.2 0.009

3.03 6 0.21a 2.34 6 0.16 2.38 6 0.18

3.20 6 0.21 2.28 6 0.19 ND

3.51 6 0.22a 2.66 6 0.17 2.51 6 0.16

0.005 0.007 0.3

1.63 6 0.22d 1.38 6 0.16 1.01 6 0.09

1.10 6 0.13 1.19 6 0.14 ND

1.41 6 0.24 1.32 6 0.19 1.05 6 0.10

,0.001 0.3 0.7

0.97 6 0.05a 0.79 6 0.05 0.77 6 0.05

0.99 6 0.05 0.77 6 0.05 ND

1.07 6 0.06a 0.84 6 0.06 0.82 6 0.05

0.04 0.04 0.2

66 (21–176) 82 (38 –227) 127 (44 –204)

53 (17–126) 89 (38 –177) ND

38 (17–147)c 70 (50 –186) 147 (55–254)

0.001 0.3 0.3

Values are the mean 6 SEM; the P value is derived from the within-group one-way ANOVA. Values for Lp(a) are presented as median and the 25th and 75th percentiles. ND, Not determined. a P , 0.05 vs. GHS and controls. b P , 0.05 vs. differences between 2 yr and baseline in GHS. c P , 0.05 vs. differences between 2 yr and baseline in controls. d P , 0.05 vs. controls.

response to the discontinuation of GH treatment. Serum Lp(a) levels were similar in all study groups throughout the study. A reduction in the Lp(a) concentration occurred after GH treatment was stopped in the GHD group, but not in the other two study groups. A covariance analysis using the mean 24-h GH concentration, baseline levels of serum IGF-I, insulin, truncal fat mass, or total BF% as individual covariants could not explain the differences in the baseline and 2-yr levels of total C, LDL-C, and apo B among the three study groups. The baseline difference in the serum level of triglycerides could, however, be explained by each of the individually above-mentioned cofactors. The 2-yr change in serum insulin concentration correlated with the change observed in serum triglycerides (r 5 0.46; P 5 0.005), and the change observed in truncal fat mass correlated with the changes seen in both serum concentrations of LDL-C (r 5 0.38; P 5 0.03) and apo B (r 5 0.42; P 5 0.01). Body composition

After the discontinuation of GH treatment and during the 2-yr observation period, BMI increased in both controls and the GHS group (Table 4). The BMI did not, however, differ significantly between the groups throughout the study. The LBM% decreased and the BF% increased in both patient groups during the 2 yr without GH treatment (Table 4). A similar tendency was found in the healthy controls. The loss of LBM% and the gain in BF% in both patient groups was more marked than in the healthy controls (Fig. 4). Before the discontinuation of GH treatment, the amount of total BF% and truncal fat increased in the GHD group compared with

levels in both GHS and control subjects. An increase in the amount of truncal fat was observed in all of the study groups, but this increase was more marked in the GHD group than in the controls (Fig. 4). As a result, 2 yr after GH treatment was stopped, the LBM% had decreased, and the BF% and the amount of truncal fat had increased in the GHD group compared with those in the GHS and control subjects. Body resistance increased in all the study groups after the discontinuation of GH treatment (Table 4). The change in body resistance was more marked in the GHD than in the other two groups. After 2 yr, body resistance had increased in the GHD group compared with the others, thereby indicating a reduction in extracellular fluid volume and fat-free mass in this group. Discussion

In this long term, prospective trial of the discontinuation of GH treatment in adolescent patients with childhood-onset GHD and short stature, only adolescents with severe GHD continuing into adulthood developed classical metabolic consequences associated with GHD in adults. Adolescents with more preserved GH secretion after discontinuation of treatment responded similarly to the longitudinal changes seen in the normal healthy adolescents. A large percentage of patients with short stature and GHD in childhood do not have severe GHD into adulthood (15). One consistent finding, however, is that subjects with organic hypothalamic-pituitary disease, an additional anterior pituitary hormone deficiency, and postirradiation GHD in childhood will most likely remain severely GH deficient into adulthood (16, 17). This experience was used in the classi-


FIG. 2. A, Serum LDL-C concentrations before and 12 and 24 months after the discontinuation of GH treatment in adolescents. One group comprised 21 adolescents with severe GHD continuing into adulthood (solid line), the second group comprised 19 adolescents with their own GH secretion (GHS; broken line), and the third group consisted of 16 healthy controls studied on two occasions with 2 yr in between. B, Percent change in serum LDL-C concentrations between baseline and 2 yr after discontinuing GH treatment in the 2 patient groups and the controls. *, P , 0.05 compared with controls; †, P , 0.05 compared with the GHS group.

fication of subjects in this trial. It is, however, a small risk that the five patients with only one additional anterior pituitary hormone deficiency were wrongly classified, as there is a small proportion of such patients who will not have severe GHD (18). The use of peak 24-h GH levels will, however, minimize that risk, as GH-deficient adults may have a lower peak that does not overlap with the peak 24-h GH concentration in normal subjects (19). We can only speculate about whether the GH levels in all of the subjects who were not classified as GH deficient are sufficient for their future health and well-being. Using previously defined criteria for severe GHD in adults, the mean 2-yr changes in the patients with severe GHD were different from those in the subjects who did not fulfill those criteria. In addition, the GH-sufficient patients had mean and peak 24-h GH concentrations similar to those in the control group. Furthermore, the GH-sufficient group and the controls displayed longitudinal changes in terms of lipoproteins and

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FIG. 3. A, Serum HDL-C concentrations before and 12 and 24 months after the discontinuation of GH treatment in adolescents. One group comprised 21 adolescents with severe GHD continuing into adulthood (solid line), the second group comprised 19 adolescents with their own GH secretion (GHS; broken line), and the third group consisted of 16 healthy controls studied on 2 occasions with 2 yr in between. B, Percent change in serum HDL-C concentrations between baseline and 2 yr after discontinuing GH treatment in the 2 patient groups and the controls. *, P , 0.05 compared with controls; †, P , 0.05 compared with the GHS group.

body composition similar to those reported in large crosssectional cohorts of healthy subjects of similar age (20, 21), indicating only that the endogenous GH secretion in the GH-sufficient group was adequate. There is limited knowledge about GH replacement therapy during the transition between childhood and adulthood, during which there is a steep decline in the GH secretion (22). The elevated serum IGF-I levels in both patient groups at baseline compared with the controls indicate that the average replacement dose of GH when entering the study was too high and that the longitudinal changes may therefore be inappropriately large in both patient groups. The duration of the study and the comparison between both patient groups and with the levels and the longitudinal changes in the controls should minimize any inappropriate interpretation of the between-group effects in this trial. The slightly higher serum IGF-I concentration in the GH-sufficient group might be influenced by their more recent onset of puberty than the GHD group, but not by different doses of GH during the last 2 yr

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TABLE 4. Body composition measurements in 40 adolescent subjects discontinuing GH treatment at final height and 16 healthy controls Variable

BMI (kg/m2) GH-deficient GH-sufficient Controls Body resistance (Ohm) GH-deficient GH-sufficient Controls Lean body mass (%) GH-deficient GH-sufficient Controls Body fat (%) GH-deficient GH-sufficient Controls Truncal body fat (kg) GH-deficient GH-sufficient Controls

Baseline

1 yr

2 yr

P value

23.2 6 0.6 22.1 6 0.6 22.3 6 0.8

23.4 6 0.8 22.3 6 0.8 ND

23.8 6 0.8 23.1 6 0.8 22.9 6 0.8

527 6 18 486 6 16 500 6 16

564 6 17 523 6 16 ND

589 6 18a,b,c 515 6 15 520 6 19

,0.001 ,0.001 0.02

72.4 6 1.9 79.4 6 2.2 77.0 6 2.8

66.1 6 1.7 75.8 6 2.4 ND

65.7 6 1.7a,c 74.6 6 2.5c 75.6 6 2.8

,0.001 ,0.001 0.06

22.7 6 2.1e 15.8 6 2.1 17.6 6 2.7

29.1 6 1.9 19.3 6 2.5 ND

29.4 6 1.8a,b,c 20.5 6 2.6c 19.0 6 2.9

,0.001 ,0.001 0.07

8.1 6 1.0a 5.1 6 0.8 5.8 6 1.3

10.5 6 1.1 6.3 6 1.1 ND

10.9 6 1.1a,c 6.9 6 1.1 6.5 6 1.3

,0.001 ,0.001 0.03

0.2 0.001 0.001

Values are the mean 6 SEM; the P value is derived from the within-group one-way ANOVA. a P , 0.05 vs. GHS and controls. b P , 0.05 vs. differences between 2 yr and baseline in GHS. c P , 0.05 vs. differences between 2 yr and baseline in controls. d P , 0.05 vs. GHS. e P , 0.05 vs. controls.

before entering the trial. Subjects with multiple pituitary hormone deficiencies could not explain why the GH-deficient group had increased total body fat and abdominal obesity at baseline compared with the groups with preserved GH secretion (data not shown). This suggests that an inappropriate replacement therapy with other hormones was not responsible for this difference. GH-deficient adults have increased secretion rate and reduced clearance rate of very low density lipoprotein (VLDL)apo B (23), explaining their increased serum concentrations of LDL-C and apo B (5). Abdominal obesity, particularly when combined with insulin resistance and hyperinsulinemia, increases VLDL-apo B secretion from the liver (24). The increased VLDL-apo B secretion in GHD is therefore most likely explained by their abdominal obesity (1) and insulin resistance (25). Short term GH treatment increases the VLDLapo B clearance rate (26). This is probably an effect of both induced action of the hepatic LDL receptor by GH (27) and increased removal of triglycerides from the VLDL particle by enhanced lipoprotein lipase activity in muscle (28). Before GH treatment was discontinued and throughout the study period, the levels of serum total C, LDL-C, and apo B were increased in the GH-deficient subjects compared with those in both groups with more preserved GH secretion. In accordance with previous studies (29, 30), this could not be explained by differences in serum concentrations of IGF-I, insulin, or body composition among the study groups. An association was found, however, between the increase in serum concentrations of LDL-C and apo B and the gain in abdominal adiposity during the 2 yr after terminating GH treatment. The increased levels of total C, LDL-C, and apo B in the GH-deficient compared with the other two study groups, therefore, remain unexplained. Probably, however, it depends on the balanced and complex effect on VLDL

metabolism by insulin sensitivity, abdominal adiposity, genetic factors, and GH status. The increased serum triglyceride levels in the GH-deficient group compared with controls at baseline and the reduction in serum triglyceride levels in response to terminating GH treatment is in contrast with observations that GH-deficient adults have increased serum triglyceride concentrations (4). Statistically, however, increased serum IGF-I concentration, increased serum insulin level, and increased abdominal adiposity could explain this increased serum triglyceride concentration at baseline. GH has profound lipolytic actions on visceral fat, increasing the availability of free fatty acids to the liver, which together with GH per se increase VLDL secretion from the liver (31). Moreover, abdominal obesity combined with hyperinsulinemia increase hepatic VLDL secretion more markedly than abdominal obesity alone (24), and patients with acromegaly have increased serum levels of triglycerides, which normalize in response to successful adenomectomy (32). Prolonged periods of inappropriately high GH levels and increased serum IGF-I and insulin concentration may therefore, together with increased adiposity, explain this contrasting finding for triglyceride levels in this study. Two years after GH treatment was discontinued, the patients with severe GHD persisting into adulthood developed an increase in the amount of body fat and an increase in abdominal fat mass, and their elevated levels of total, LDL-C, and apo B concentrations increased further compared with those in subjects with more preserved endogenous GH secretion and healthy controls. Moreover, the reduction in HDL-C concentration contrasted with the increase observed in the GH-sufficient group and the controls. Although a reduction occurred in serum insulin and Lp(a) levels in the GHD group after stopping GH treatment, the levels of insulin


FIG. 4. A, Truncal fat mass before and 12 and 24 months after the discontinuation of GH treatment in adolescents. One group comprised 21 adolescents with severe GHD continuing into adulthood (solid line), the second group comprised 19 adolescents with their own GH secretion (GHS; broken line), and the third group consisted of 16 healthy controls studied on 2 occasions with 2 yr in between. B, Percent change in truncal fat mass between baseline and 2 yr after discontinuing GH treatment in the 2 patient groups and the controls. *, P , 0.05 compared with controls; †, P , 0.05 compared with the GHS group.

and Lp(a) did not differ from the levels seen in the controls during the study, making these changes less important. Two years after GH treatment was discontinued, the GH-deficient group was therefore characterized by metabolic features previously well known from cross-sectional studies of adult patients with GHD (33, 34). Abdominal obesity is an important risk factor for cardiovascular morbidity and mortality in both men and women (35, 36). Moreover, high concentrations of LDL-C and low levels of HDL-C are associated with a high incidence of cardiovascular morbidity and mortality (37). Intima-media thickness is an important surrogate variable for the progression of atherosclerosis and its manifestations (38, 39). Young adults with GHD of childhood onset have increased intimamedia thickness of the common carotid arteries (40), which is normalized by GH replacement therapy (41). This finding together with the great importance of the total cholesterol level in early adult life for cardiovascular disease in midlife (42) demonstrate the significance of the metabolic conse-

4523

quences of discontinuing GH treatment in adolescents with severe GHD persisting into adult life. The overall cardiovascular risk profile at baseline together with the metabolic deterioration observed during the 2 yr without GH treatment in the GH-deficient adolescents may therefore be of major importance for their future cardiovascular health. The increase in cardiovascular mortality seen in long term survivors of childhood neoplasia (43) may be explained in part by neuroendocrine aberrations. This particularly applies to children who have received cranial irradiation. They may develop features of the metabolic syndrome, with an increase in body weight, abdominal obesity, hyperinsulinemia, and low serum HDL-C concentrations (44). These are all characteristics that can be explained by the high prevalence of GHD found in these subjects (45). The eight subjects in this trial with GHD as an effect of previous neoplasia and radiation therapy did not differ from the 13 subjects with other causes of GHD (data not shown). This suggests that the metabolic consequences of GHD found in this trial were an effect of the hormone deficiency rather than its cause. The increase in BF% and the decreases in LBM% and extracellular fluid volume observed when GH treatment was stopped were expected from previous small scale, short term trials of the discontinuation of GH treatment in adolescents (10 –12). What is, however, clearly demonstrated in this trial is that the loss of LBM and the increase in BF are more marked in subjects with severe GHD compared with those with preserved GH secretion. Two years after discontinuing GH treatment for GHD in childhood and short stature, subjects with severe GHD continuing into adulthood accumulated metabolic features that may disadvantageously affect their future cardiovascular health. Although it has not been proven that GH replacement therapy in adults saves lives, it is clear that the treatment improves the overall metabolic profile in GH-deficient adults (1, 46). Adolescents with severe GHD continuing into adulthood should, therefore, be considered for GH replacement therapy continuing into adult life. Acknowledgments We are indebted to Per Arne Lundberg for his excellent biochemical support, Ingvar Bosaeus for his support on the body composition data, and Lena Wireń, Anne Roseń, Ingrid Hansson, and Sigrid Lindstrand at the Research Center for Endocrinology and Metabolism for their skillful technical support.

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