Page 288 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Intersexuality
The development of the gonadal anlagen to taining Y chromosome fragment onto an X
ovaries and testes is fixed by the presence or chromsome. In Turner’s syndrome (XO) con-
absence of the testis-determining factor (TDF), nective tissue strands are formed in place of
which is encoded on the sex determining re- normal ovaries and the external features are
gion of the Y chromosome (SRY) and is respon- more likely to be female (→ A4). The condition
sible for testicular development (→ A1). Ova- is characterized by a number of additional
ries develop if TDF is absent (→ A2). The go- malformations (e.g., of the heart and kidneys;
nads determine the formation of female and dwarfism, webbed neck).
male sexual hormones. Testosterone is formed In certain mutations of the SRY gene no
in the Leydig cells of the testes, while anti- functional TDF is formed, despite the presence
Müller hormones are formed in the Sertoli of a male chromosome set (XY), and ovaries
cells (Müller inhibition factor [MIF]; → A1). develop (→ A5).
However, not only androgens but also proges- In true hermaphroditism both testes and
togens (some of them precursors of testoster- ovaries are simultaneously formed (→ A6). An
one formation) and estradiol (predominantly XY/XO mosaic can be a cause. Translocation of
by peripheral transformation of testosterone) some parts of the Y chromosome, including of
Hormones trogens and, to a lesser extent, also androgens XX male, see above) can lead to the formation
are formed in the male. Progestogens and es-
the SRY gene, onto an X chromosome (as in the
of bisexual gonads and the appearance of in-
(mainly androstendion) are produced in the
In pseudohermaphroditism the gonads cor-
The development of the Wolffian ducts to
9 ovaries (→ A2). tersexual sex characteristcs.
internal male genitals (epididymis and vas respond to the chromosomal sex, but the sex
deferens) is stimulated by the androgens, organs and secondary sex characteristics di-
while the development of the Müller ducts to verge or are not unequivocal. In male pseudo-
form the internal female genitals (fallopian hermaphroditism intersexual or female sex
tubes, uterus, vagina) is suppressed by the characteristics are present (→ A7). A gonado-
anti-Müller hormone from the Sertoli cells. tropin deficiency may be a cause, for example
The external sexual characteristics are deter- when gonadotropin release is suppressed due
mined, first and foremost, by the concentra- to an increased formation of female sexual
tion of androgens (→ p. 272), whereby the de- hormones by a tumor. Other causes can be de-
velopment of the female genitals and some of fects in the gonadotropin receptor, aplasia of
the sexual characteristics is promoted by es- the Leydig cells, enzyme defects of testoster-
trogens. one synthesis (→ p. 264), defective testes,
The sex of an individual can be defined on absent conversion of testosterone into dihy-
the basis of the chromosomal set (XX or XY, re- drotestosterone (reductase deficiency), or de-
spectively), of the gonads (ovary or testis), of fective androgen receptors (→ p. 272). In rare
the internal organs or of external appeareance. cases the formation of the female genitals
Intersexuality occurs when the various sex may not be suppressed owing to a defect in
characteristics have not developed unequivo- the release or action of the anti-Müller hor-
cally or are more or less pronounced. mone. Female pseudohermaphroditism (→
An abnormal chromsome set occurs, for ex- A8) can be the result of iatrogenic administra-
ample, in Klinefelter’s syndrome (XXY), in tion or increased formation of androgens, for
which the testes are formed in such a way example in an androgen-producing tumor, or
that spermatogenesis is possible, but androgen can be due to an enzymatic defect in adreno-
production is impaired (→ A3). The androgen cortical hormone synthesis, or a defect of aro-
deficiency then leads to an inadequately male matase, which transforms androstendion or
appearance. Only mild clinical symptoms are rather testosterone into estrogens (→ p. 264).
present in the XYY syndrome. A similar condi-
278 tion prevails in the XX male syndrome, which
is probably due to translocation of an SRY-con-
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
All rights reserved. Usage subject to terms and conditions of license.