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Androgen Insensitivity Syndrome

The term Androgen insensitivity syndrome (AIS) refers to an X-chromosome-linked recessive mutation resulting in undervirilization of male external genitalia. The degree to which external genitalia are “feminized” is dependent on the functionality of the androgen receptor. Deletion of its gene results in complete AIS (CAIS). In CAIS, an individual's external genitalia appear female. Reduction in androgen receptor functionality results in partial AIS (PAIS). PAIS is graded on the extent of feminization of external genitalia, which can be ambiguous at birth. Most individuals with AIS are infertile but face virtually no other morbidity or mortality. Treatment includes extended psychological support and hormone therapy. The overall incidence of AIS is 5 in 100,000 live male births. CAIS is slightly more common than PAIS.

Pathophysiology

Between the 8th and 10th week of gestation, male gonads begin producing testosterone, dihydrotestos-terone (DHT), and Miillerian inhibiting factor (MIF), which are hormones critical to male development. In AIS, normal amounts of hormones are produced, but properly functioning androgen receptors for testosterone and DHT are absent. While MIF causes internal male development, unopposed testicular estrogen causes external female genital development.

Presentation

All individuals with AIS lack internal female reproductive organs and do not menstruate, though the conversion of testosterone to estradiol enhances breast development. Only individuals with the mildest forms of PAIS are fertile. Most individuals have sparse armpit and pubic hair.

In CAIS, individuals have labia, a clitoris, and at most, the distal two thirds of the vagina, though sometimes only a dimple is present. Because individuals with CAIS look female, they are rarely diagnosed in childhood unless a mass in the lower abdomen or groin is felt and imaging or surgery reveals an undescended testis. More often, CAIS individuals present to a physician during puberty when they fail to menstruate.

In PAIS, there may be undescended testes, a small penis, placement of the urethal opening on the underside of the penis, an enlarged clitoris or fused labia. Due to ambiguity, PAIS is often diagnosed in childhood. Otherwise, individuals will present to a clinician during puberty. If male identified, they are often concerned about breast development. If female identified, they are often concerned about the lack of menstruation.

Diagnosis and Treatment

Diagnosis is confirmed by the presence of a Y chromosome, male levels of testosterone and DHT, and, on imaging, intra-abdominal testes or an absent uterus.

In addition to long-term counseling for individuals and families, support groups play a significant role in treatment. Gender-appropriate hormone therapy is usually started at puberty. Eventually, testes are surgically removed to prevent intra-abdominal testicular cancer that could be missed on physical examination.

Optional, cosmetic treatments include nonsurgical lengthening of the vagina, vaginal construction, or clitoral reduction. Breast reduction and repositioning of the urethral opening are surgical options in male-identifying AIS patients. It is recommended by clinicians, ethicists, and patient advocates that surgery occur only when a patient can give full and informed consent.

RishiRattan
http://dx.doi.org/10.4135/9781412964517.n24
See also

Further Readings

Sytsma, S. E. (Ed.). (2006). Ethics and intersex. Dordrecht, The Netherlands: Springer.http://dx.doi.org/10.1007/1-4220-4314-7
Warne, G. L. (1997). Complete androgen insensitivity syndrome. Parkville, Australia: Royal Children's

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