Androgen Insensitivity Syndrome

What is androgen insensitivity syndrome?
Androgen insensitivity syndrome is a condition that affects sexual development before birth and during puberty. People with this condition are genetically male, with one X and one Y chromosome. Because their bodies are unable to respond to certain hormones (called androgens), they may have mostly female sexual characteristics or signs of both male and female sexual development (hermaphroditism).
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. People with partial androgen insensitivity (also called Reifenstein syndrome) can have normal female sexual characteristics, both male and female sexual characteristics, or normal male sexual characteristics. People with mild androgen insensitivity appear male, but are often infertile and tend to develop female breasts at puberty.
How common is androgen insensitivity syndrome?
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.

What genes are related to androgen insensitivity syndrome?
Mutations in the AR gene cause androgen insensitivity syndrome.
The AR gene provides instructions to make a protein called an androgen receptor. This protein allows cells to respond to androgens, which are hormones (such as testosterone) that direct male sexual development. Androgens and androgen receptors also have other important functions in both males and females, such as regulating hair growth and sex drive. Mutations in the AR gene prevent the androgen receptor from working properly, which makes cells less responsive to androgens or prevents cells from using these hormones at all. Depending on the level of androgen insensitivity, an affected person's sexual characteristics can vary from mostly female to mostly male.
Read more about the AR gene.

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 mutated 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 in each cell is sufficient to cause the condition. Males are affected by X-linked recessive disorders much more frequently than females. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
About two-thirds of cases are inherited from mothers who carry an altered copy of the AR gene on one of their two X chromosomes. The remaining cases result from a new mutation in a mother's egg cell before the child is conceived.