Adapted from the chapter, Sex and Intersex.
"Intersex" describes many different ways in which sex development goes wrong. Where sex manifests in genes, hormones, primary sex characteristics, and secondary sex characters, variation in sex occurs in all these areas too.
Because sex and gender are different, an intersex person is not necessarily transgender. Intersex advocates are quick to point out that intersex does not fit under the transgender umbrella as gender identities like transexual and genderqueer. I agree wholeheartedly because intersex refers to sex and not gender and because "transgender" is a voluntary group and we don't force people to join. Intersex people were formerly referred to as "hermaphrodites" but is now depreciated for being derogatory and clinically problematic.
To get an idea of the diversity, here are some of the more common intersex conditions. For more detail, I recommend the Intersex Society of North America and their website www.isna.org.
Turner syndrome is similar to to Klinefelter's but features a karyotype with one too few chromosomes instead of one too many. Affected people have only one X chromosome and no Y chromosome (written as "XO"). They are phenotypical females. One in 50 every conceptions have Turner syndrome but only 2% survive pregnancy.(www.isna.org/faq/conditions/turner) Again, because of regular X inactivation, the person is able to live without great effects after birth.Josef Kirchner is a ex-trans poster child turned genderqueer who is XY/XO.
One type of mosaicism is mixed gonadal dysgenesis where the gonads are radically different. One may be an ovary and the other a teste or one may be an ovo-teste, a gonad with some ovarian cells and some testicular cells.
ambiguous genitalia." They may also have increased body hair, malformed ovum leading to infertility. and may be mistaken for boys. In all cases there are serious health risks. 10% of intersex people with CAH identify as transgender.PEDIATRICS Vol. 118 No. 2 August 2006, pp. 753-757 as seen on http://pediatrics.aappublications.org/cgi/content/full/118/2/753
A variant of AIS is partial AIS (PAIS) where the body only partly reacts to androgens. This can cause ambiguous genitalia or non-intersex male infertility. People with PAIS may identify as male or female. There are other intersex conditions with the same effects of AIS but different cause where the SRY gene is absent of mutated and unable to function.
Various simpler intersex condition exist where everything is normal except that the genitals display a single abnormality. These include a very small penis (micropenis), a very large clitoris (clitoromegaly), the absence of either a clitoris or penis (aphallia) or hypospadias. Hypospadias affects males in whom the urethra has not moved to the tip of the penis and is somewhere in between the tip of the penis and its original location between the labia (which have formed into the scrotum).
Note: I simplified some data. Regarding genitals, "Any" includes penis and scrotum, clitoris and vagina, or ambiguous. Regarding gonads, "Any" includes ovaries, testes, or ovo-testes. Regarding second sex characteristics, "Any" includes traditional female, traditional male, or anywhere in between. Regardnig gender identity, "Any" includes women, men, genderqueer or bigender. Of course, any intersex person may have a genderqueer or bigender identity. The only identities listed are the most common. Prevalence based on a global population of 6.5 billion people.