Intersex can be divided into four categories:
- 46, XX Intersex
- 46, XY Intersex
- True Gonadal Intersex
- Complex or Undetermined Intersex
Each one is discussed in more detail below. Note: In many kids the cause of intersex may remain undetermined, even with modern diagnostic techniques.
46, XX Intersex. The person has the chromosomes of a woman, the ovaries of a woman, but external (outside) genitals that appear male. This usually is the result of a female fetus having been exposed to excess male hormones before birth. The labia ("lips" or folds of skin of the external female genitals) fuse, and the clitoris enlarges to appear like a penis. Usually this person has a normal uterus and Fallopian tubes. This condition is also called 46, XX with virilization. It used to be called female pseudohermaphroditism. There are several possible causes:
- Congenital adrenal hyperplasia (the most common cause).
- Male hormones (such as testosterone) taken or encountered by the mother during pregnancy.
- Male hormone-producing tumors in the mother. These are most often ovarian tumors. Mothers who have children with 46, XX intersex should be checked unless there is another clear cause.
- Aromatase deficiency. This one may not be noticeable until puberty. Aromatase is an enzyme that normally converts male hormones to female hormones. Too much aromatase activity can lead to excess estrogen (female hormone); too little to 46, XX intersex. At puberty, these XX children, who had been raised as girls, may begin to take on male characteristics.
46, XY Intersex. The person has the chromosomes of a man, but the external genitals are incompletely formed, ambiguous, or clearly female. Internally, testes may be normal, malformed, or absent. This condition is also called 46, XY with undervirilization. It used to be called male pseudohermaphroditism. Formation of normal male external genitals depends on the appropriate balance between male and female hormones; therefore, it requires the adequate production and function of male hormones. 46, XY intersex has many possible causes:
- Problems with the testes: The testes normally produce male hormones. If the testes do not form properly, it will lead to undervirilization. There are a number of possible causes for this, including XY pure gonadal dysgenesis.
- Problems with testosterone formation: Testosterone is formed through a series of steps, where each requires a different enzyme. Deficiencies in any of these enzymes can result in inadequate testosterone and produce a different syndrome of 46, XY intersex. Different types of congenital adrenal hyperplasia can fall in this category.
- Problems with using testosterone: Some people have normal testes and make adequate amounts of testosterone, but still have 46, XY intersex.
- 5-alpha-reductase deficiency. People with 5-alpha-reductase deficiency lack the enzyme needed to convert testosterone to dihydrotestosterone (DHT). There are at least five different types of 5-alpha-reductase deficiency. Some of the babies have normal male genitalia, some have normal female genitalia, and many have something in between. Most change to external male genitalia around the time of puberty.
- Androgen insensitivity syndrome (AIS). This is the most common cause of 46, XY intersex. It has also been called testicular feminization. Here the hormones are all normal, but the receptors to male hormones don't function properly. There are over 150 different defects that have been identified so far, and each causes a different type of AIS.
True Gonadal Intersex. Here the person must have both ovarian and testicular tissue. This may be in the same gonad (an ovotestis), or the person might have one ovary and one testis. The person may have XX chromosomes, XY chromosomes, or both. The external genitals may be ambiguous or may appear to be female or male. This condition used to be called true hermaphroditism. In most people with true gonadal intersex, the underlying cause is unknown, although in some animal studies it has been linked to exposure to common agricultural pesticides.
Complex or Undetermined Intersex Disorders of Sexual Development. Many chromosome configurations other than simple 46, XX or 46, XY can result in disorders of sex development. These include 45, XO (only one X chromosome), and 47, XXY, 47, XXX -- both cases have an extra sex chromosome, either an X or a Y. These disorders do not result in a condition where there is discrepancy between internal and external genitalia. However, there may be problems with sex hormone levels, overall sexual development, and altered numbers of sex chromosomes.