Gary Waters Getty Images. As a clinical geneticist, Paul James is accustomed to discussing some of the most delicate issues with his patients.
But in early , he found himself having a particularly awkward conversation about sex. A year-old pregnant woman had visited his clinic at the Royal Melbourne Hospital in Australia to hear the results of an amniocentesis test to screen her baby's chromosomes for abnormalities. The baby was fine—but follow-up tests had revealed something astonishing about the mother. Her body was built of cells from two individuals, probably from twin embryos that had merged in her own mother's womb.
And there was more. One set of cells carried two X chromosomes, the complement that typically makes a person female; the other had an X and a Y. Halfway through her fifth decade and pregnant with her third child, the woman learned for the first time that a large part of her body was chromosomally male.
Sex can be much more complicated than it at first seems. According to the simple scenario, the presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female.
But doctors have long known that some people straddle the boundary—their sex chromosomes say one thing, but their gonads ovaries or testes or sexual anatomy say another. Parents of children with these kinds of conditions—known as intersex conditions, or differences or disorders of sex development DSDs —often face difficult decisions about whether to bring up their child as a boy or a girl.
