Klinefelter Syndrome in Adolescence - The Journal of Clinical ...

Wikström et al. Testicular Degeneration in Adolescent KS Boys J Clin Endocrinol Metab, May 2004, 89(5):2263–2270 2267
FIG. 2. Patient 2, group I (Table 1). Electron micrograph of testicular
biopsy of boy with KS at age 10.1 yr and Tanner stage P1G1. Undifferentiated
Sertoli cells resembling Sa type with a round nucleus with
a small nucleolus lacking lamellar body and with crystalloids from
Charcot-Bötscher. In the center, one degenerating Sertoli cell
(magnification, 2500).
testosterone had reached 2.5 nmol/liter, a marked drop in
serum AMH had already occurred (Fig. 4B).
Discussion
With the aid of modern infertility treatment technologies
such as ICSI, some men with KS may father children. However,
in adulthood, when these treatments come into consideration,
the testes of most KS men are completely atrophied.
In the current work we investigated whether
adolescent patients with KS have germ cells and evaluated
whether early puberty is the optimal period for retrieving
germ cells for further use in ICSI. Although this concept has
gained further actuality with the recent report of a successful
extraction of sperm-containing tissue from a 15-yr-old boy
with KS (20), it has not been previously investigated
systematically.
We found, surprisingly, that in early adolescence as many
as 50% of the boys with KS had germ cells in their testes and
that the depletion of these cells accelerated at the onset of
puberty. This presence of germ cells during peripuberty contrasts
with results of a report by Müller et al. (5), in which no
germ cells were detectable in KS boys beyond the age of 2 yr.
A probable explanation is that all boys in Müller’s publication
were cryptorchid, whereas none in our group had any
history of testicular maldescendent. Cryptorchidism is
known to cause marked decrease in germ cell numbers also
in boys with a normal karyotype (21, 22).
Ad spermatogonia that develop postnatally from fetal
spermatogonia under gonadotropin and testosterone stimulation
are of fundamental importance for the development
of male fertility (23). In the boys with KS, the fact that the
number of these cells was markedly reduced indicates a
severely impaired fertility potential even in early puberty.
Furthermore, we observed only type A spermatogonia in our
boys with KS, which suggests an arrest in germ cell development
at the stage of A spermatogonia. Normally, type A
spermatogonia transform into type B spermatogonia and
further to the first primary spermatocytes at the age of 5 yr
(18, 24). At present, whether this defect in spermatogenesis
in the XXY testis is intrinsic to germ cells or due to the
inability of the Sertoli cells to support normal germ cell
development is unknown. A defect in Sertoli and germ cell
communication in the differentiating XXY testis has been
suggested (25).
Activation of the hypothalamic pituitary testicular axis
was associated with depletion of germ cells. A strong correlation
appeared between an increasing testosterone level
and suppression of the Sertoli cell markers inhibin B and
AMH. It is possible that the molecular mechanisms induced
by the altered dosage of X-encoded genes in testicular cells
may accelerate loss of germ cells. For example, the androgen
receptor gene is located on the X chromosome (26).
The testicular volume of KS boys is already below normal
during childhood (1.0–1.5 ml; normally 1.8 ml) (27, 28). During
puberty their testes grow (11, 12), which was also observed
in the current work (Figs. 3 and 5). In healthy boys,
the proliferation of germ cells is predominantly responsible
for the pubertal growth of the testes (29, 30). Because we
could detect no spermatogenesis beyond the development of
type A spermatogonia and the number of these cells was low,
the pubertal testicular growth in KS boys was due almost
solely to the proliferation of Sertoli cells and interstitial cells.
This might suggest that the immature Sertoli cells of boys
with KS are responding to the pubertal increase in FSH
stimulation, as seen in boys with a normal karyotype. On the
other hand, the prepubertal Sa and Sb cells were not capable
of transforming into the adult Sc cell type, and the degeneration
of Sertoli cells increased markedly during puberty. It
is therefore tempting to hypothesize that the regression of the
testes in KS includes Sertoli cell degeneration. Consistently,
electron microscopy revealed degenerating Sertoli cells, a
rare finding in testes of healthy early pubertal boys.
The concept of Sertoli cells in boys with KS regressing after
the initial phase of Sertoli cell proliferation during early
puberty is in agreement with changes observed in serum
levels of inhibin B (31). This glycoprotein is thought to reflect
Sertoli cell function during prepuberty and become germ cell
dependent during midpuberty (32). In our cohort of boys
with KS, serum inhibin B levels during prepuberty and early
puberty were normal (33–35), and measurable inhibin B levels
did not fully correlate with the presence of germ cells in
the testes. This suggests that during early puberty, serum
inhibin B levels in boys with KS reflect the integrity or number
of Sertoli cells or both. A normal inhibin B level and a low
testosterone level were also shown to be inconsistent with the
presence of spermatogonia (group IIA in Tables 1 and 2 and
Fig. 4A).
AMH or Müllerian-inhibiting substance, a glycoprotein
dimer of the TGF family, is expressed in prepubertal but not
adult Sertoli cells (36). Serum AMH levels remain high