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The Intersex Spectrum
by Carl Gold
Physical gender is not always just a matter of XX or XY, girl or boy. In
approximately one out of every 100 births, seemingly tiny errors occur during
the various stages of fetal sex differentiation, causing a baby's body to
develop abnormally. Problems in the formation of chromosomes, gonads, or
external genitals can lead to a range of intersex conditions. The most common
and well-researched of these conditions are explained below. For information on
intersex conditions not mentioned here, see
http://www.hopkinsmedicine.org/pediatricendocrinology/.
Congenital Adrenal Hyperplasia (CAH)—One in 13,000 births
Two hormones are critical in normal sex differentiation. The testes of normal
46,XY males secrete both Müllerian Inhibiting Substance (also known as MIS
or antimüllerian hormone) and masculinizing androgenic hormones, while the
ovaries of a normal 46,XX female secrete neither. In CAH, the absence of a
critical enzyme allows a 46,XX fetus to produce androgens, resulting in
ambiguous external genitals. A CAH individual may have an oversized clitoris
and fused labia.
Testosterone Biosynthetic Defects—One in 13,000 births
In a condition related to CAH, some 46,XY individuals do not have the properly
functioning enzymes needed to convert cholesterol to testosterone. When such
enzymes prove completely incapable of creating testosterone, the genitals
appear female; when the enzymes function at a low level, ambiguous genitals
form.
Androgen Insensitivity Syndrome (AIS)—One in 13,000 births
AIS affects the section of the 46,XY population that is physically unable to
react to androgens. In Complete AIS (CAIS), testes exist in the abdomen while
the external genitals are female. The Wolffian, or male, duct structures do not
form because of the lack of response to androgens. The Müllerian, or
female, duct structures do not evolve because the testes still release MIS. At
puberty, CAIS individuals grow breasts but do not menstruate. The testes are
sometimes removed from the abdomen because they may develop cancer.
Partial AIS (PAIS) is marked by a limited response to androgens. The external
genitals are ambiguous and duct development is incomplete. Depending on the
selection of hormone treatment, PAIS individuals may exhibit partial male or
partial female development at puberty.
Gonadal Dysgenesis—One in 150,000 births
In gonadal dysgenesis, the androgen receptors are intact while the
androgen-secreting testes are not. Complete Gonadal Dysgenesis, in which
neither androgens nor MIS are produced, yields female genitals and
Müllerian duct formation, despite a genetic profile suggesting maleness.
With estrogen treatment, female puberty can be achieved. Partial Gonadal
Dysgenesis results in ambiguous genitals and duct development, as some
androgens and MIS are produced. Like PAIS, the choice of hormone treatments
determines the physical gender of the adult with Partial Gonadal
Dysgenesis.
5-Alpha Reductase Deficiency—No estimate available
5-Alpha Reductase is the enzyme that facilitates the conversion of testosterone
to another hormone, dihydrotestosterone (DHT). When a genetic male is deficient
in 5-Alpha Reductase, the powerful DHT hormone is not produced. While testes
and Wolffian ducts do exist, the male external genitals are similar in size to
those of a normal female. If left intact, an adult 5-Alpha Reductase Deficiency
individual will appear generally male but with small genitals and no facial
hair.
Micropenis—No estimate available
In order to create a proper penis in a 46,XY individual, androgens must be
secreted twice during fetal life. First, the androgens help to shape the basic
structures into a penis and scrotum; later, the androgens enlarge the penis. A
micropenis is the result of normal androgen secretion in the first stage and
little or no androgen secretion in the second. The penis is normal in shape and
function, but extremely small in size. While earlier surgeons often converted
micropenises to female genitals, today micropenises are often left intact.
Individuals with intact micropenises are often given testosterone to stimulate
masculinizing puberty.
Klinefelter Syndrome—One in 1,000 births
Sometimes chromosomes join but do not form standard 46,XX or 46,XY
combinations. Individuals with Klinefelter Syndrome are genetically 47,XXY and
live as men. Small penis and testes, low androgen secretion, and possible
female breast development are characteristics of this syndrome.
Turner Syndrome—No estimate available
Like Klinefelter Syndrome, Turner Syndrome is marked by an abnormal karyotype,
45,XO. While Turner women have female external genitals, the individuals lack
properly formed ovaries. Without estrogen treatment, no breast growth occurs.
Other possible features of Turner Syndrome include short stature, webbing of
the neck, and misshapen internal organs.
Timing Defect—No estimate available
If all of the proper stages of normal male sex differentiation occur, but the
timing is incorrect by just days, errors may arise. The occasional outcome in a
46,XY individual with this timing defect is ambiguous external genitals.
Note: The information above was adapted from "Syndromes of Abnormal Sex
Differentiation," written by physicians at The Johns Hopkins Children's Center
in Baltimore, Maryland. The statistics on frequency were obtained from the
Intersex Society of North America (www.isna.org).
Carl Gold is a former intern at NOVA Online.
Photos: WGBH/NOVA
My Life as an Intersexual |
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Two Sexes Are Not Enough
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© | Updated November 2001
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