Radiology wrote:
CS is XXY with testosterone levels above the "accepted" values to compete as a women. Hence, she is required to lower testosterone levels in order to compete.
According to the CAS decision in Semenya's case, and other documents released by the IAAF/WA, Caster Semenya - and all the other DSD athletes in women's track who have to lower their natural testosterone to compete in women's events - are 46,XY with testosteroe levels in the normal male range.
These athletes have male levels of testosterone because they have well-developed, functioning testes.
XXY is a male-only condition where a male person has an extra X chromosome ; it's also known as Klinefelter syndrome. Males who are XXY are unambiguously male from birth; therefore, they don't "have form" for competing in women's sports.
Semenya has XY 5-ARD2, an enzyme deficiency that occurs in both sexes, but which is a DSD only in males. Male fetuses with 5-ARD2 develop normal testes that produce the large amounts of testsosterone that males normally produce; and they also have normal male response to the massive amounts of T they make. But their enzyme deficiency causes them to have underdeveloped prostates and to be born with penises that are minuscule, malformed or missing altogether. As a result, they are often mistakenly thought to be female at birth.