Androgen Insensitivity Syndrome

Androgen Insensitivity Syndrome - complete and partial androgen insensitivity syndrome

The androgen insensitivity syndrome (AIS) typically includes evidence of feminization (i.e., undermasculinization) of the external genitalia at birth, abnormal secondary sexual development in puberty, and infertility.

Complete androgen insensitivity syndrome affects 2 to 5 per 100,000 live male births. Partial androgen insensitivity is at least as common as complete androgen insensitivity. Mild androgen insensitivity is much less common.

Androgen insensitivity syndrome (AIS), formerly known as testicular feminization, is an X-linked recessive condition resulting in a failure of normal masculinization of the external genitalia in chromosomally male individuals. This failure of virilization can be either complete androgen insensitivity syndrome (CAIS) or partial androgen insensitivity syndrome (PAIS), depending on the amount of residual receptor function. Complete androgen insensitivity syndrome occurs when the body cannot use androgens at all. Partial or mild androgen insensitivity syndrome results when tissues are partially sensitive to the effects of androgens .

Major changes in the understanding and management of the various forms of AIS have occurred since 1990. Laboratory research has greatly expanded our understanding of the molecular mechanisms of the clinical features, including a rare neuromuscular disorder. More importantly, patient advocacy groups for AIS and other intersex conditions have increased public awareness of these disorders, helped revise our understanding of gender identity, emphasized the value of accurate and sophisticated information for patients, and induced physicians to re-evaluate the effectiveness of the surgical corrections attempted in past decades. Surgery is increasingly seen as a very elective option even for the more ambiguous conditions.

Diagnosis of Androgen Insensitivity Syndrome

AIS can be subdivided into three phenotypes:

1. complete androgen insensitivity syndrome (CIAS),
2. partial androgen insensitivity syndrome (PAIS), and
3. mild androgen insensitivity syndrome (MAIS).

The diagnosis of CAIS is usually made on clinical findings and laboratory evaluations alone. The diagnosis of PAIS and MAIS may also require a family history consistent with X-linked inheritance.

How do people inherit androgen insensitivity syndrome?

This condition is inherited in an X-linked recessive pattern. A condition is considered X-linked if the gene that causes the disorder is located on the X chromosome (one of the two sex chromosomes ). In males, who have only one X chromosome , one altered copy of the gene is sufficient to cause the condition. Males are affected by X-linked recessive disorders much more frequently than females.

About two-thirds of cases are inherited from a woman who carries an altered copy of the AR gene on one of her two X chromosomes . The other one-third of cases result from a new mutation in a mother's egg cell before the child is conceived.

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Site last updated: March 4, 2008

Androgen Insensitivity Syndrome - complete and partial androgen insensitivity syndrome