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My new nephew was born with 48,XXYY Syndrome, which is a condition that I now hear about for the first time. It is very rare, isn't it? Does anyone have any figures? I am looking for info about the prevalence of 48,XXYY Syndrome in the United States or North America as a whole. Thanks.


Hello, I'm the moderator for an online support group for family's with boys who have XXYY Syndrome. It is part of the XXYY Project. We are the only organization just for family's with boys who have xxyy. From the latest research studies, XXYY Syndrome affects anywhere from 1 in 18,000 to 1 in 40,000 live male births. So it's probably somewhere in the middle of that number. We have several papers written up on the latest research. Please have your nephew's parents contact us, if they haven't already. They can write to me at or
they can go to our website at

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