Anyone born with a genital or 23rd pair chromasomal abnormality has an "Intersex Condition".
Such is society's longing for normalcy, that it only allows for 2 sexes. Male and Female, Black and White. People born Intersex are neither, they are, to extend the analogy, a lovely shade of Grey.
However, dependent on their chromasomal makeup, they are usually assigned to one gender or the other at birth, either electivly (Such as in Kleinfelter's Syndrome where the child is outwardly male, but has an XXY chromasomal make up or Turner's Syndrome where the child is outwardly female, but has an XO chromasomal makeup}, or by surgery if there is any Genital Ambiguity.
This is to engender their integration into society, but as you can guess, sometimes it doesn't work out like that.
People assigned to what they feel as "The wrong sex" by hasty surgery at their birth have to then undergo another Sex Change to become the sex they felt they should have been all along. Others are forced into Hormone treatments at puberty, again to "make them conform to society norms" and find that they are rapidly and usually irreversibly swallowed up by the treatment.