Androgen Insensitivity Syndrome

Androgen Insensitivity Syndrome

Androgen insensitivity syndrome (AIS) is a disorder caused by mutation of the gene for the androgen receptor. This protein binds testosterone and regulates the expression of other genes that stimulate male sexual development. Testosterone is the principal male androgen. AIS is an X-linked recessive disorder that completely or partially prevents development of male sexual characteristics despite the presence of the Y chromosome. Thus, the phenotype of a person with AIS, typified by female or ambiguous sexual characteristics, is at odds with the genotype, which includes the presence of both the X and Y, or male-determining, chromosomes.

The extent of the syndrome ranges from complete androgen insensitivity and development of normal external (but not internal) female sexual anatomy, to partial insensitivity, with altered or ambiguous male or female genitals, to mild insensitivity, with normal male genitals, enlarged breasts, and possibly impotence. Treatments depend on the extent of the syndrome, and may include hormone therapy, surgery, and psychological counseling. Gene testing and genetic counseling are available for families with affected members.

Sexual Development

AIS can best be understood against the background of normal human sexual development, which begins in the womb. The gonads arise from the same embryonic tissue, which is differentiated into one or the other by the actions of several genes not involved in AIS.

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