By some estimates 1 in 60 people are born with some combination of male and female anatomy and/or chromasomes.
Some are surgicly altered at birth to 'normalise' them. Which can cause lifelong complications and, if the guessed gender doesn't suit then the person will often end up transgender whether they know they were born intersex or not.
IS definately doesn't explain the majority of CDs and TSs, but still a significant minority of CDs and TSs armay well be IS.
So, are you intersex? Do you know someone who is?