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The Journal of Clinical Endocrinology & Metabolism 90(12):6424 – 6430
Copyright © 2005 by The Endocrine Society
doi: 10.1210/jc.2005-1081
Salutary Effects of Combining Early Very Low-Dose
Systemic Estradiol with Growth Hormone Therapy in
Girls with Turner Syndrome
Robert L. Rosenfield, Nancy Devine, Joanne Julius Hunold, Nelly Mauras, Thomas Moshang, Jr., and
Allen W. Root
The University of Chicago Pritzker School of Medicine (R.L.R., N.D.), Chicago, Illinois 60637; Genentech, Inc. (J.J.H.),
South San Francisco, California 94080; Nemours Children’s Clinic (N.M.), Jacksonville, Florida 32207; University of
Pennsylvania (T.M.), Philadelphia, Pennsylvania 19104; and University of South Florida (A.W.R.), Tampa, Florida 33701
Context: Optimizing pubertal estrogen replacement in girls with
Turner syndrome is important.
Interventions: Depot estradiol, 0.2 mg/month im, was given initially
and gradually increased; GH was 0.05 mg/kg daily.
Objective: The study objective was to test the hypotheses that physiological estradiol replacement administered early with GH will preserve height potential as much as if administered late and that it will
bring about a greater height gain than standard oral estrogen therapy
combined with GH.
Main Outcome Variable: Adult or near-adult height was the main
outcome variable.
Design: The study was randomized to early or late estrogen treatment; follow-up was at 3.5 yr or later.
Setting: This was a multicenter outpatient study.
Patients: Turner syndrome girls 12.0 –12.9 yr (n ⫽ 7) or 14.0 –14.9
yr (n ⫽ 7) of age who began GH before age 12.0 yr were the patients.
The girls were matched to National Cooperative Growth Study registry patients who began GH and oral conjugated estrogen at similar
ages and were similarly followed to adult or near-adult height.
D
ETERMINING THE ESTROGEN replacement regimen
that is optimal for use with GH therapy has become
a practical issue in the management of teenage girls with
Turner syndrome. The secretion of estrogen during adolescence contributes to the growth spurt of early puberty (1, 2).
This effect appears to be due both to direct effects on cartilage
growth (3) and to an increase in GH secretion (4). The estrogen effect on growth is biphasic, stimulatory at low doses,
but inhibitory at higher doses (5). Low doses of estrogen
stimulate linear growth in hypogonadal girls; depot estradiol
at 1.5–2.0 mg per month (1) and ethinyl estradiol in a dose
of approximately 0.12 mg monthly (4 ␮g daily) (6) increase
height velocity. Higher estrogen doses inhibit growth (6, 7),
in part by direct effects on epiphyseal senescence and fusion
(8, 9) and in part by acting as GH antagonists (10, 11).
Customary oral estrogen replacement therapy clearly is
detrimental to growth potential when administered at 12 yr
of age. Chernausek et al. (12) added estrogen to GH therapy
of girls with Turner syndrome at either 12 or 15 yr of age, and
First Published Online September 27, 2005
Abbreviations: BA, Bone age; NCGS, National Cooperative Growth
Study.
JCEM is published monthly by The Endocrine Society (http://www.
endo-society.org), the foremost professional society serving the endocrine community.
Results: Depot estradiol treatment resulted in height significantly
taller than predicted at 12 yr of age (P ⬍ 0.02). All height potential
was gained in the first 2 yr of the study, during which the early group
grew 3.5 cm more than the late group, which was receiving GH alone
(P ⬍ 0.01). The early depot estradiol group also gained 5.9 cm more
height after starting estrogen than did the early National Cooperative
Growth Study group (P ⬍ 0.05). Although feminization proceeded
slowly on the lowest dose of estradiol, it advanced normally thereafter.
Conclusions: These results suggest that very low-dose parenteral
estradiol permits relatively age-appropriate feminization without interfering with the effect of GH on the enhancement of height potential.
(J Clin Endocrinol Metab 90: 6424 – 6430, 2005)
the patients were followed from 12 yr of age until near-adult
height. Conjugated equine estrogens were administered as
0.3 mg daily for the first 6 months and subsequently 0.6 mg
daily, at which time cyclic medroxyprogesterone acetate was
added. The total growth from 12 yr of age averaged 13.0 cm
in the group that began estrogen at 12 yr, whereas it averaged
15.8 cm in the group that began estrogen at 15 yr; this difference was highly significant.
We have postulated that estradiol delivered into the systemic circulation in a dosage regimen approximating the low
amount of estradiol normally produced during early puberty
would provide a physiological form and amount of estrogen
that would emulate natural puberty with respect to both
feminization and the pubertal growth spurt and so could be
started at a normal age without loss of growth potential. If
so, it would remove the dilemma faced by Turner syndrome
patients—whether to forgo age-appropriate feminization to
increase adult height. In 1991 we began enrolling Turner
syndrome patients as young as 12 yr of age into a multicenter
study to address this possibility in patients receiving recombinant GH treatment. Estradiol was administered in a depot
form (estradiol cypionate) as a monthly injection starting at
a dose (0.2 mg monthly) well below any previously reported.
Preliminary data analysis was performed after nine patients
had undergone 1.5–2.0 yr of estradiol therapy (13). This anal-
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Rosenfield et al. • Early Physiological Estradiol Replacement
J Clin Endocrinol Metab, December 2005, 90(12):6424 – 6430
ysis suggested that height potential was promoted by combining early pubertal amounts of estradiol with GH treatment for 1.5–2.0 yr, supporting the concept that early, very
low replacement doses of estrogen might preserve height
potential while allowing adequate, timely feminization.
Therefore, we continued to enroll patients into the study and
have now followed them to near-adult or adult height. These
results, reported in this study, support the hypothesis that
very low doses of systemically administered estradiol promote growth in response to GH when given as young as
12–13 yr of age, while simultaneously stimulating a generally
normal pace of pubertal development. Thus, they indeed
seem to be physiological.
Subjects and Methods
Study subjects
The institutional review boards of each of the four participating
centers approved these studies. Subjects with Turner syndrome were
recruited after giving informed written consent. Their clinical characteristics are summarized in Table 1.
Study procedures
Fourteen patients were recruited to undergo site-balanced randomization to begin estradiol “early” (12.0 –12.9 yr of age) or “late” (14.0 –14.9
yr of age) during their 12th year of age (Fig. 1). These two groups had
been receiving GH since 10.0 ⫾ 1.2, sem, and 9.5 ⫾ 0.4 yr of age,
respectively. Natural sequence recombinant GH (Nutropin) was provided by Genentech on a “no cost to patient basis” through a combination of insurance and a grant program. Dosage was maintained
throughout the study at 0.05 mg/kg daily sc, divided into six or seven
daily doses. A baseline height velocity was calculated for the preceding
6 months. If possible, patients were maintained on the protocol until they
achieved adult or near-adult height; these were respectively defined as
an annualized growth velocity less than 1.25 cm/yr and 1.25–2.5 cm/yr
in the preceding 6-month period.
Depot estradiol (estradiol cypionate; Depo-Estradiol), which consists
of 67% estradiol, was administered locally as single monthly im injec-
6425
tions while the subjects continued to receive GH therapy. The starting
dose of depot estradiol was 0.2 mg; the dose was then increased at
successive 6-month intervals by 0.2 mg initially and by 0.5 mg after a
dose of 1.0 mg was reached, to a maximum of 3.0 mg monthly. Doses
less than 1.0 mg were prepared by dilution of stock Depo-Estradiol (5
mg/ml) to a concentration of 1.0 mg/ml of cottonseed oil under sterile
conditions. Progestin was not prescribed until after 4 yr of estradiol
therapy unless irregular menstrual bleeding occurred; this was the case
in two subjects (A and D). Every 6 months, height, pubertal stage, and
bone age (BA) were documented on case report forms on which the dates
of the last estradiol and GH injections were recorded, and a blood sample
was drawn and urinalysis performed, with rare individual exceptions.
Prospective BA determinations by the pediatric endocrinologist at
each study site, using the method of Greulich and Pyle, were used for
computations of height prediction, after the principal investigator determined that the results did not differ significantly from his blind
readings of all available BA films before therapy (14). Height predictions
were determined from the fraction of height achieved at each of these
BA, according to the method of Bayley and Pinneau (15). Serum was
frozen at ⫺70 C until it was assayed in one batch at the University of
Chicago Hospital Endocrinology Laboratory upon completion of the
study. Estradiol was assayed by a sensitive immunoassay kit (Pantex,
Santa Monica, CA) (16), LH and FSH by immunometric assay kits specific for the gonadotropin ␤ subunits (Delfia, PerkinElmer, Boston, MA)
(17), and IGF-I by an immunometric assay kit (Nichols, San Clemente,
CA). Complete blood count, urinalysis, thyroid function tests, and blood
sugar were monitored locally.
Statistical analysis
Within-group comparisons were made by paired Student’s t test, and
comparisons between the early and late estradiol treatment groups were
made by unpaired Student t test. P values are two-tailed; P ⬍ 0.05 was
considered statistically significant.
We secondarily compared the growth of these patients to that of
Turner syndrome patients on oral estrogen treatment, as recorded in the
National Cooperative Growth Study (NCGS) registry. We matched our
subjects to all registry patients who had started GH treatment for a
similar lead-in time before 12.0 yr of age, had received conjugated equine
estrogen replacement for at least 1.5 yr commencing at either 12.0 –12.9
or 14.0 –14.9 yr of age, and had been followed to adult or near-adult
height. Conjugated equine estrogen was the most commonly specified
TABLE 1. Growth parameters in study group
At 12.0 –12.9 yr of age
Case
Karyotype
Age
(yr)
Early estradiol treatment
A
45X
12.0
B
45X/
12.1
46XXqi
C
45X
12.3
D
45X
12.3
E
45X
12.6
F
45X
12.9
G
45X
12.9
Mean
12.4
Late estradiol treatment
H
45X/
12.3
46Xxqi
I
45X
12.3
J
45X
12.3
K
45X/
12.8
46XXqi
L
45X
12.3
M
45X/46XY
12.6
Meanb
12.4
At 14.0 –14.9 yr of age
At end of study
Height
(cm)
BA
(yr)
PAH
(cm)
Age
(yr)
Height
(cm)
BA
(yr)
PAH
(cm)
Age
(yr)
Height
(cm)
BA
(yr)
HT VEL
(cm/yr)
Menarche
(yr)
135.1
138.9
11.0
12.0
149.1
150.7
14.0
14.1
147.1
150.1
13.0
13.3
153.5
155.1
18.0
16.6
156.7
155.5
16.0
16.0
0.60
0.00
14.50
137.5
130.4
137.0
131.7
146.6
136.7
10.5
11.0
10.0a
9.9
13.0
11.1
153.5
142.0
152.9a
151.2
153.0
150.3
14.3
14.3
14.6
14.7
14.9
14.4
149.2
143.6
151.0
145.1
159.9
149.4
13.5
13.0
14.0
13.1
13.0
13.3
153.2
149.1
154.1
151.0
165.9
154.6
15.3
16.3
15.8
16.7
15.9
16.4
151.5
148.6
154.1
149.8
162.0
154.0
15.0
15.5
15.0
16.5
13.5
15.4
2.28
0.21
0.00
0.71
0.60
0.60
13.25
14.80
139.4
11.0
154.8
14.3
147.4
12.0
158.2
16.3
155.5
ND
1.20
132.0
137.4
143.0
11.0
11.0
12.0
143.8
149.7
155.1
14.4
14.5
14.8
143.1
146.1
150.7
13.0
12.5
13.5
148.4
154.0
154.3
17.0
16.3
16.4
151.4
151.2
153.6
ND
ND
14.5
2.05
1.20
0.62
142.9
141.4
138.0
12.0
11.0
11.3
155.0
154.0
150.8
14.3
14.6
14.5
151.9
151.9
146.8
13.5
12.5
12.8
156.0
160.1
153.7
16.5
152.9
PAH, Predicted adult height; HT VEL, height velocity.
a
BA and PAH computed from data at 12.2 yr because BA was not obtained at 12.6 yr.
b
Means are shown for those in the late treatment group followed to near-adult or adult height (cases H–K).
1.29
14.25
15.40
17.8
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J Clin Endocrinol Metab, December 2005, 90(12):6424 – 6430
Rosenfield et al. • Early Physiological Estradiol Replacement
FIG. 1. Study design schema. Both early and late estradiol
treatment groups received the same cumulative dose of
estradiol in each year of estradiol therapy. mo, Month.
form of estrogen; eight had started it early and 11 late; the starting dose
was specified as 0.3 mg daily in 80% of each group. The outcomes for
the early and late NCGS groups were compared with the corresponding
depot estradiol groups by two-sample, two-tailed t test.
Results
The study groups were of similar age, height, BA, and
predicted adult height at the time of randomization into the
early or late estradiol treatment group in their 12th year of
age (Table 1). Six of the seven in the early estradiol treatment
group were followed until attainment of adult height, and
three of the four remaining in the late estradiol treatment
group did so. Three randomized to the late estradiol treatment group dropped out of the study before achieving nearadult or adult height; two (L and M in Table 1) terminated
participation at 14.8 and 15.6 yr of age after 6 and 12 months
of estradiol treatment, respectively, when breast development had not occurred or was minimal (stage 2), respectively,
so their data were available for some analyses; the other
dropped out at 12.4 yr of age immediately after learning of
assignment to the late estradiol group, so there were no data
to be evaluated. Sufficient height was achieved for three
subjects in the early treatment group to discontinue GH
treatment after 3 yr, including one who had not yet attained
adult height (C in Table 1). All but one study subject discontinued the GH treatment during their 15th or 16th year,
even the two who still had not attained adult height.
As a whole, the subjects treated with this estradiol replacement regimen reached adult or near-adult heights significantly greater than predicted at 12 yr of age (P ⬍ 0.02).
They achieved all of this increase in height potential by the
end of the second year of the study, whether they received
GH alone or GH plus estradiol. Their height at the end of the
study was similar to their height predictions at 14 yr of age.
The early estradiol treatment group grew 17.3 ⫾ 0.9 cm,
sem, from the start of the study at 12.0 –12.9 yr of age until
adult or near-adult height (from 136.7 ⫾ 2.0 cm in the beginning to 154.0 ⫾ 1.7 cm by the end of the study). Although
they were 1.3 cm shorter at the beginning of the study, they
grew 2.3 cm more than those treated with GH alone over this
same period of time. Although the difference in overall
growth between early and late estrogen-treated groups during the study was not statistically significant, the early treatment group tended to exceed their 12-yr height prediction by
1.6 cm more than the late treatment group (P ⬍ 0.07).
Most of the growth of the early-estrogen-treated patients
took place during the first 2 yr of adding estradiol to GH
therapy. During this time, they grew 3.5 cm more than those
on GH alone: 12.7 ⫾ 0.4 cm, sem, vs. 9.2 ⫾ 0.6 cm; P ⬍ 0.01
(Fig. 2). The bulk of this increase in growth occurred on the
lowest doses of estradiol, which induced significant increases
in height velocity within the first 1.5 yr of estradiol replacement, and particularly within the first 6 months (Fig. 2).
Coincidentally, their height potential increased from 150.3 ⫾
1.5 to 154.6 ⫾ 2.0 cm in the first 2 yr of the study because their
BA did not advance disproportionately. Consequently, their
height potential increased by 4.3 cm, from 150.3 ⫾ 1.5 to
154.6 ⫾ 2.0 cm at 14 yr of age, which proved to be similar to
their height at the conclusion of the study.
The late estradiol treatment group grew 15.0 ⫾ 1.9 cm from
study start at 12.25–12.8 yr of age until adult or near-adult
height (from 138.0 ⫾ 2.3 cm to reach an average adult height
of 152.9 ⫾ 1.0 cm) (Table 1). Those followed to the end of the
study grew 8.9 ⫾ 0.8 cm on GH treatment alone during the
first 2 yr of the study, and then grew 6.1 ⫾ 1.3 cm during the
remainder of the study after estradiol treatment was added
to GH. Their growth on estradiol was significantly less (P ⬍
0.01) than that experienced by the early estradiol treatment
group during their first 2 yr of estradiol therapy, but not
significantly different than the 4.6 ⫾ 1.0 cm after 14 yr of age
FIG. 2. Height and height velocity (mean ⫾ SEM) of the groups treated
early and late with depot estradiol, according to study year. Estradiol
replacement was begun at the point indicated by the arrows (solid
arrows and data points indicate early group; open arrows and data
points indicate late group). The groups averaged 12.4 yr of age at
study yr 0. The number of subjects in each group at each time point
is indicated between the graphs. There is a missing data point for
height at 3.0 yr in the late group for a patient who was studied for 3.5
yr. Numbers above error bars are P values. Note that the number of
subjects for whom heights were obtained after study yr 2.0 differs
from the number followed to adult or near-adult height, in part because of patients achieving sufficient height for them to discontinue
the study at different points in the study.
Rosenfield et al. • Early Physiological Estradiol Replacement
by the early estradiol group. Height potential of subjects
treated with GH alone from 12–14 yr of age increased from
152.1 ⫾ 2.7 to 155.2 ⫾ 1.7 cm, and the height in those followed
to the end of the study was similar to that predicted at 14 yr
of age (Table 1). The 3.1-cm increase in height potential while
on GH therapy alone, before estradiol was begun, was not
significantly different from the increase in height potential
experienced simultaneously by the study group treated with
the combination of GH and early estradiol during that time.
The group treated late with estradiol did not experience a
clear pubertal growth spurt (Fig. 2). The only hint of a
growth-promoting effect of estradiol in these patients was a
slight upward deflection from their previously steadily waning response to GH over time. This suggestion of increased
growth occurred 1.0 –1.5 yr after estradiol was begun, on the
0.4- to 0.6-mg dosage of depot estradiol, not on the initial,
lowest estradiol dose on which peak height velocity of the
early treatment group occurred.
The group treated early with estradiol also gained significantly more height after the institution of estrogen (17.3 ⫾
0.9 cm) than did the NCGS comparison group treated early
with oral conjugated estrogen (11.4 ⫾ 1.5 cm) (Fig. 3). The
gain in height after the institution of estrogen was not significantly different between the two forms of estrogen replacement in those whose treatment was begun late (14.0 –
14.9 yr of age), however.
Feminization proceeded slowly on the lowest dose of estradiol (Fig. 4). Nearly half of the study subjects did not
experience breast budding (stage 2) during the first 6 months
of therapy. Thereafter, breast development advanced to maturity by an average of one stage in response to each incremental increase in estradiol dose. By the end of 2 yr of
treatment, breast development was present in all, and ranged
from stage 2–5, with most patients attaining stage 3 or 4; the
girl with the slowest pace of breast development experienced
the slowest BA advancement (case G). Five of the eight study
subjects who received estradiol for 2.5 yr menstruated during
the study period; menarche occurred at an average of 2.0 yr
J Clin Endocrinol Metab, December 2005, 90(12):6424 – 6430
6427
FIG. 4. The percentage of study subjects achieving the designated
stage of breast development at check-ups after the initiation of estradiol treatment. The number of subjects at each time point is shown
at the bottom of columns. The development of menarche (M) is indicated for individual subjects at their corresponding breast stage. Note
that the dose of estradiol was gradually escalating throughout the
study (see bottom scale).
(between 1.4 and 2.5 yr) after the initiation of estradiol therapy in all of these, but did not occur within 4 yr otherwise.
Notably, two girls in the early treatment group did not experience menarche during the second 2-yr study period although they had been at stage 4 of breast development for
2.5 yr and were on an adult dose of depot estradiol (3.0 mg
monthly).
Hormonal responses obtained 3–9 d after depot estradiol
injections were analyzed with respect to the estradiol dose
because this is the time during which estradiol levels peak
(18). Figure 5A shows that there was a linear relationship
between estradiol dose and plasma level. The correlation,
although weaker than expected (r ⫽ 0.59), is significant and
contrasts with the lack of evidence for a suppressive effect of
estradiol on plasma IGF-I levels (Fig. 5B). Figure 5C depicts
a significant biphasic response of FSH levels to depot estradiol throughout the course of the study. All patients were
euthyroid throughout the study period. No adverse reactions
occurred.
Discussion
FIG. 3. Total height gain from 12.0 –12.9 yr of age for subjects treated
from that age (early) or from 14.0 –14.9 yr of age (late) to adult or
near-adult height with either depot estradiol (DE2) or conjugated
estrogen (NCGS) in conjunction with GH. Those treated early with
DE2 experienced an average of 5.9 cm more linear growth than those
treated early with conjugated estrogen (P ⬍ 0.05).
As a whole, the patients treated with this very low-dose
estradiol regimen reached an average adult height significantly greater than that predicted before therapy (P ⬍ 0.02).
It is notable that the increase in height prediction by 14 yr of
age (P ⬍ 0.05) accounted for all of the increase in adult height.
Adult height of each group came within 0.8 cm of that predicted at 14 yr. Consequently, all of the GH effect on growth
enhancement occurred by 14.0 yr of age, and it is clear that
this estrogen replacement regimen did not interfere with the
GH effect on height enhancement. Indeed, these data suggest
that very low-dose estradiol replacement therapy at 12 yr of
age in conjunction with GH therapy may improve adult
height.
These data support the notion that, in conjunction with
GH, very low-dose, systemic estradiol administered early
(12.0 –12.9 yr of age) preserves height potential as much as
when administered late (14.0 –14.9 yr). Furthermore, the
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J Clin Endocrinol Metab, December 2005, 90(12):6424 – 6430
Rosenfield et al. • Early Physiological Estradiol Replacement
FIG. 5. Hormonal responses to depot estradiol 3–9 d after injection, the time at which estradiol levels reach plateau levels before declining.
Linear regression analysis indicated that there was a linear effect of estradiol dose on plasma estradiol level (A), but not on IGF-I level (B).
Polynomial regression analysis indicated that FSH (C) falls with increasing estradiol dosage up to 1.0 mg monthly, but rises thereafter; this
is probably related to the decrease in sensitivity to estradiol-negative feedback that occurs over time during neuroendocrine puberty. Conversion
of mass units to SI units: estradiol picograms per milliliter ⫻ 3.671 ⫽ picomoles per liter; IGF-I nanograms per milliliter ⫻ 0.131 ⫽ nanomoles
per liter.
overall growth of the early treatment group from 12.0 yr to
adult height tended to be greater than in the group in which
estradiol treatment began late (P ⫽ 0.07), and those treated
with estradiol early tended to reach a slightly greater adult
height. Notably, the early treatment group grew significantly
more between 12.0 and 13.5 yr of age while receiving the
combination of 0.2– 0.6 mg depot estradiol monthly and GH
than did the other group, which was only on GH during this
time. Although both groups, taken as a whole, reached an
adult height significantly greater than predicted 4 yr earlier,
during their 12th year of life, their adult height was virtually
identical to their predicted adult height during their 14th
year of age. This was the case whether they received GH plus
estradiol or GH alone throughout this time (early or late
estradiol treatment group, respectively). These data indicate
that the low doses of depot estradiol, less than 0.8 mg/
month, used during the first 1.5 yr of treatment did not
interfere with GH-induced growth enhancement and stimulated growth without deleteriously affecting height potential and possibly promoting it. This suggests that this form
of estradiol treatment is particularly efficacious when administered at an age (in the 12th year) and BA (about 11 yr)
appropriate for early puberty. Conversely, after 14.0 yr of age
(at BA about 12.75 yr) there appears to be no advantage to
using such a low dosage of estradiol compared with 1.0 –1.5
mg monthly, which we previously reported to be growthstimulatory at that age without compromising adult height
potential and which brings about the more rapid tempo of
pubertal change that is desirable at that age (1, 19).
These conclusions are buttressed by the secondary comparison of overall growth of those treated early with depot
estradiol to a matched group of NCGS subjects who were
treated with conjugated estrogen at a similar age and followed to near-adult or adult height. Those treated with depot
estradiol grew significantly more over the same span of time,
by an average of 5.9 cm.
A significant linear relationship was found between depot
estradiol dose and serum estradiol levels 3–9 d after depot
estradiol injection, at which time unconjugated estradiol levels peak as they are hydrolyzed from the cyclopentylpropionate ester (18). However, the blood levels of estradiol were
lower by half than predicted from the earlier study; this may
be related to the high variance of the responses, which in turn
may be related to technical problems in local administration
of the small injection volume. No such evidence of a suppressive effect of these estradiol doses on IGF-I levels was
found. A biphasic effect of estradiol dose on serum FSH
levels was observed, such that the low doses of estradiol used
early in treatment were more FSH-suppressive than were the
higher doses employed as the girls aged. This may be related
to the previously documented decrease of sensitivity of the
“gonadostat” to negative feedback by estrogen with advancing age and neuroendocrine puberty (1).
Our experience also suggests that feminization issues become as important as height issues for 14-yr-old girls with
Turner syndrome, contrary to the expectation of most U.S.
pediatric endocrinologists (20). The desire for a faster pace of
feminization was the sole reason for drop-out from the group
randomized to start estradiol late; three of the seven subjects
assigned to this group left the study before achieving adult
or near-adult height. The tempo of feminization on this estradiol replacement regimen was slightly slower than average (21); this was primarily because breast budding did not
occur in one third of the patients on the starting dose (0.2 mg
monthly) of depot estradiol. After 2 yr of estradiol therapy,
one of the 11 patients had still only achieved stage 2 breast
development; nevertheless, eight of the 11 patients had attained stages 3 or 4 and one had achieved stage 5. This
variability is compatible with marked individual differences
in target organ sensitivity. Two of the 11 experienced menarche during this time. By the end of 3 yr of therapy, 80% had
experienced menarche, but those who had not done so did
not experience periods in the subsequent one or more years
of follow-up. The delayed menarche in these patients is likely
to be due to the study design, which did not call for progestin
replacement before 4 yr, because these patients both had
been in breast stage 4 for over 2 yr and were on a full adult
replacement dose of estradiol. Not only does feminization
become increasingly important by 14 yr of age, no further
growth is gained by delaying it beyond the 12th year of age
when using this estradiol treatment regimen, for these doses
of estrogen clearly did not interfere with the response to GH
therapy.
These studies indicate that a very low level of estradiol
Rosenfield et al. • Early Physiological Estradiol Replacement
administered systemically promotes optimal pubertal
growth, which was the rationale for the study. The mechanisms for these observations are not fully characterized. An
abundant body of data supports the concept that oral and
systemically administered estrogen have differential effects
in vivo (11, 13). Oral estrogens, by first passage through the
portal circulation may impair the expression of the GH receptor and IGF-I generation, essentially functioning as GH
antagonists. These effects are not observed with physiological doses of systemically administered estrogen.
Our study is also consistent with the concept that the
various forms of estrogen may differ in their effects. The
growth-stimulatory dose of estradiol appears to be quite
broad: this study demonstrates that depot estradiol doses in
the range of 0.2– 0.6 mg monthly stimulate growth beyond
that attributable to GH alone, whereas our earlier study, in
the absence of GH supplementation, showed that a dosage
of 1.0 –1.5 mg monthly is likewise growth-stimulatory (1).
Because one third of depot estradiol consists of the fatty acid
ester, this indicates that estradiol is growth-stimulatory over
the dose range of 0.13–1.0 mg monthly. This contrasts with
the very narrow growth-stimulatory profile of ethinyl estradiol; it stimulates growth at a dosage of about 4 ␮g daily, i.e.
0.12 mg monthly, but not at a dosage 2- to 4-fold more (6).
Even lower doses may accelerate bone maturation disproportionately in young girls (22). These considerations suggest previously unsuspected differences between the effects
of estradiol and ethinyl estradiol. Ethinyl estradiol contains
an ethinyl group covalently bound to estradiol, and this bond
protects it from first-pass hepatic metabolism on oral consumption; furthermore, it is not metabolized to estradiol and
instead binds to the estrogen receptor in unmodified form,
where it has a more prolonged receptor occupancy time than
estradiol itself (23).
Our study also demonstrates that the timing of estrogen is
another determinant of its effect. The lowest dose of estrogen
was growth-stimulatory only when administered to the
younger group of patients, i.e. 12 yr olds. This effect was not
seen when the same dose was started in the older group (14
yr olds) after two extra years of GH therapy. This phenomenon is reminiscent of the poor growth spurt observed when
puberty is allowed to resume after the discontinuation of
gonadotropin suppression treatment of sexual precocity (24).
This timing effect is consistent with a model in which growth
plate chondrocytes have a finite proliferative potential (8)
that is accelerated independently by GH or low doses of
estradiol until a point at which senescence curtails the capacity for replication in response to hormonal stimulation.
Unfortunately, optimal vehicles for administering the very
low doses of estradiol necessary for physiological estrogen
replacement therapy during puberty are not commercially
available. The very low estradiol dosage that we have used
is inconvenient to administer because the dose is so low that
it requires a compounding pharmacist to prepare a sufficiently dilute solution of the commercially available stock
solution to permit reasonably accurate dosimetry. However,
it may be possible to replicate the pattern of estradiol delivered in this study by using the recently developed transdermal method of delivering estradiol directly into the systemic circulation. A 14-␮g estradiol patch and a 25-␮g
J Clin Endocrinol Metab, December 2005, 90(12):6424 – 6430
6429
estradiol patch applied for 10 d per month would deliver
about the same amount of estradiol over about the same
period of time as do the respective 0.2 and 0.4 mg doses of
depot estradiol. Thus, it may be possible to administer similarly growth-promoting, very low doses of estradiol by using fractional or intermittent transdermal patch dosing (25).
In conclusion, this study suggests that the dose, route,
form, and timing of estrogen are important determinants of
estrogen effects on growth. These data demonstrate that very
low-dose, systemic estradiol administered early (12th year of
age) with GH enhances height velocity more than GH alone,
while preserving height potential. Indeed, growth from the
12th year to adult height tended to be greater in the early
treatment group and exceeded that of a matched group that
received conjugated estrogens over the same period of time.
The very low starting dose of estradiol did not bring about
feminization in one third of subjects, yet it was the most
growth-stimulatory. This raises the possibility that minimally feminizing, very low-dose estradiol replacement could
be started at somewhat younger ages without deleterious
effects on growth.
Acknowledgments
The authors thank Dr. Anne Johanson for her support in initiating this
study and the study coordinators who followed the patients.
Received May 16, 2005. Accepted September 1, 2005.
Address all correspondence and requests for reprints to: Robert
Rosenfield, M.D., The University of Chicago Comer Children’s Hospital,
Section of Pediatric Endocrinology, 5841 South Maryland Avenue, MC5053, Chicago, Illinois 60637. E-mail: [email protected].
These studies were supported in part by a grant from the Genentech
Foundation.
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