Between XX and XY: Intersexuality and the Myth of Two Sexes by Gerald Callahan

Author:Gerald Callahan [Callahan, Gerald]
Language: eng
Format: epub
Tags: Science, Life Sciences, Genetics & Genomics, Social Science, Gender Studies
ISBN: 9781569762912
Google: HlG-8bSgDBgC
Amazon: B005HF3Q40
Publisher: Chicago Review Press
Published: 2009-06-30T18:30:00+00:00

Normal Chromosomes Wearing Abnormal Genes

Like a typewriter with a bad key, sometimes a chromosome taps out a story peppered with mistakes. Every time the writer reaches for an “o,” the typewriter slaps down an “e.” “Looking forward” becomes “leeking ferward.” The sense of it blurs and the story takes an abrupt swing.

When a chromosome does that, people change in unpredictable ways.

Besides the genes found on X and Y chromosomes, there are several other genes involved in the sexual development of the fetus. We already know of nearly two dozen such genes, and undoubtedly there are more. A detailed consideration of the enzymes involved in sex development— the nature of each of these enzymes and the corresponding genes, as well as the consequences of mutations—is more than this book can handle. But with so many genes involved, the alternative outcomes of fetal sexual development are like the birds of the air—varied and wondrous. But, also like birds, some are so especially wondrous they deserve a little more attention.

Congenital Adrenal Hyperplasia

Within the urogenital ridge—what will become the external and internal genitalia of the fetus—the gonads and related sexual tissues develop close to the kidneys and the adrenal glands. The adrenal glands, like the gonads, produce hormones critical to determining the sex of the developing child. These hormones include cortisol and the adrenal androgens, especially androstenedione, a precursor to testosterone. When the adrenal glands overdevelop—a condition called congenital adrenal hyperplasia—they can produce enormous quantities of cortisol and adrenal androgens. This can cause otherwise normal 46,XX fetuses to develop clitorises that to varying degrees more closely resemble penises and scrotums—female pseudohermaphrodites.

Mutations in at least five different genes can cause congenital adrenal hyperplasia. And changes in each of these genes cause a distinct set of chemical and physical changes in the child. Baby girls begin to look like baby boys. One of these genes is responsible for an enzyme called 21-hydroxylase. Mutations in this gene result in masculinization of the external genitalia during fetal development.

Interestingly, mutations in the gene for 21-hydroxylase are some of the most common mutations seen in infants. In some populations, such as the Ashkenazi Jews, as many as one in three babies have abnormal 21-hydroxylase genes, as do one in seven people in New York City and one in sixty people in the general population.13 The symptoms vary considerably from person to person, but genetic heritage clearly plays a role.

Changes in the fetus range from simple clitoral hypertrophy (a large clitoris that may more closely resemble a penis) with normal ovaries, vagina, and uterus, to retention of the urogenital sinus, which is the space where the urethra and vagina usually come together to form a single opening to the exterior of the body. On the other hand, some 46,XY fetuses with congenital adrenal hyperplasia develop like 46,XY fetuses without adrenal problems, and the external genitalia of these infants look like those of a traditional male at birth.

Intersex as a Way of Life Among Other Animals

For those who imagine males and females as opposite sexes, hyenas are a conundrum.

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