Any experiences of Koolen Devries syndrome?

[Nimbostratus100]

Copied from "Chat" because I think it was the wrong place
My 6 year old cousin has this syndrome. I have only met him twice in the past, and he would not interact with strangers at all. Is this typical? We are thinking of inviting family for a brief visit over Christmas, but not sure if this is manageable. I'm not well, and having unknown children with not understood special needs visiting might be to much. But I do want to get to know him. His mother has serious mental health problems, and cant really be approached for information, as she gets too upset. I have not met the father, and there is very little about this condition online.
Any information at all about how it might be possible to make this child welcome and happy in my home would be very welcome - and once I know what is likely to be needed, I will be in a better position to judge whether I am actually in a position to provide what would be needed to invite the family over
Thank you

Hi. I have two friends whose children both have KdeV syndrome (we met 20 years ago on an internet forum for children with special needs when they were babies!) They are both young adults now of course.

Both male, and look so similar they could be brothers. However one is living in supported living, actually has a part time job and a girlfriend. He has moderate to severe learning disabilities but is very sociable, if repetitive.
The other lad appears as severely autistic: he is non verbal (uses an ipad with augamentitive communication app) and does not interact socially at all, very limited eye contact. Totally different. However his understanding is much better than it would appear!
So, like any other syndrome.. there is a spectrum of abilities.

I think rather than asking about the syndrome (as it's rare, only recently given a name and really just gives you a list of possible problems) it might be more useful to just ask.. what does he like? How does he communicate? What makes him smile? And take it from there :)

Thank you for your input @StillMedusa thats helpful