Androgen Insensitivity Syndrome

What is androgen insensitivity syndrome?

Androgen insensitivity syndrome is a genetic condition which affects a child’s sexual development before birth and during puberty. People with this syndrome are genetically male (they carry both an X and a Y chromosome), but are born with all or some of the physical traits of a female. This happens because a mutation on the X chromosome causes the body to resist androgen, the hormones that produce a male appearance.

There are two categories of androgen insensitivity syndrome: complete and partial.

  • In complete androgen insensitivity syndrome, the body does not respond to androgen at all. This form of the syndrome occurs in as many as 1 in 20,000 births.
  • In partial androgen insensitivity syndrome, the body responds partially to androgen. Partial androgen insensitivity occurs at about the same rate as complete androgen insensitivity syndrome. 

Signs and symptoms

Infants with complete androgen insensitivity syndrome appear to be female at birth, but do not have a uterus, fallopian tubes or ovaries. Their testicles are hidden inside the pelvis or abdomen. Breasts develop during puberty, but there is little or no pubic and armpit hair. Babies born with complete androgen insensitivity syndrome are typically raised as girls and have a female gender identity. In many cases, they aren’t diagnosed until adolescence or later, when they fail to menstruate or are unable to get pregnant.

Babies born with partial androgen insensitivity syndrome may have sexual characteristics that are typical of a male, a female, or both. They may have a partial closing of the outer vagina, an enlarged clitoris and a short vagina. They may be raised as males or as females and have a male or female gender identity.

Other symptoms of partial androgen insensitivity syndrome include failure of one or both of the testicles to descend into the scrotum after birth and an abnormal penis in which the urethra opens on the underside, instead of at the tip. In the least severe cases, the only sign of androgen insensitivity syndrome is male infertility.

Cause

Androgen insensitivity syndrome is an inherited condition passed down by the mother. A baby’s sex is determined at the moment of conception when the mother contributes an X chromosome and the father contributes either an X or a Y chromosome. Testosterone signals an XY fetus to develop male sex organs. In androgen insensitivity syndrome, a defect on the X chromosome fully or partially blocks testosterone’s effect on the body. This prevents the fetus from responding to the male hormone, interfering with the development of the sex organs.

Testing and diagnosis

Complete androgen insensitivity syndrome may be discovered in infancy when a testicle is felt as a mass in the groin or abdomen. However, in most cases, the syndrome isn’t diagnosed until adolescence or later.

Partial androgen insensitivity may be diagnosed at birth because of the presence of male and female sexual traits.

Tests used to confirm this condition include blood work to check hormone levels, genetic testing and pelvic ultrasound.

Treatment

Complete androgen insensitivity syndrome is treated with estrogen replacement therapy after puberty. Undescended testicles will be surgically removed because of the risk that they will become cancerous.

Treatment for partial androgen insensitivity syndrome may include corrective surgery to match gender identity. If your child identifies as male, hormone therapy will include testosterone.

Ongoing psychological support is an important part of treatment. Parents of a newly diagnosed child may benefit from counseling as well.

Outlook

Children with androgen insensitivity syndrome will become infertile as adults. However, with psychological support and hormone replacement therapy, they are able to otherwise lead a normal life.