I have heard similar beofre.
dd1 was born in Africa; we came back to the UK when she was 5 months old (we are boht white Europeans)
I have often wondered about possible links/triggers for dd1/
what I have come up with (PERSONAL OPINION ONLY) is:
pesticide use (especially of pesticides now banned here in UK and Europe) is far higher in Kenya (where we were). It is totally unregulated, and I would say could very well have an impact on a susceptible person/child/foetus.
the same goes for vaccinations - dd1 had a lod of jabs as a newborn, which she wouldn't have had if born in the UK (cholera, typhoid etc) some of these we didn't want her to have (TB and hep B spring to mind, prob others too). we told the nurse not to give those jabs (I was still in hospital at this point - dd1 was 3 days old). nurse misunderstood, thought we were being pfb about dd1 being in pain. gave the jabs, and said "there. all done, she barely noticed". hep B has a partic. dodgy record in terms of reactions - especially regarding intestinal disorders, iirc (dd1 now reacts to a number of foods)
when we came back to the uk, dd1 did seem to withdraw a little. we didn't have a house immediately, and we spent a couple of weeks staying with various frinds/family (moved around every 3/4 days so as to not outstay wecome)
dd1 was very stressed by this, and I have owndered whther this was a possible trigger for her. our life in Kenya was very quiet, really with just dh, me and dd1 around. and then we suddenly bunged her into the middle of all these people. new sounds (city traffic etc) new smells, new sights. must have been very confusing and overloading for her.
and then back to jabs again - the hv couldn't be bothered to work out how and where dd1 fitted into the baby jabs schedule (she had had 3 in 1, instead of 4in1 etc) so she just re-did the lot.
if I knew then what I know now, etc, etc but I didn't. so dd1 had double most baby jabs, plus the extras form Kenya, and add in to that that whenever a jab looks like having a dodgy record, it's usually offloaded into Africa/developing world etc (cynical, me?) and it doesn't look good.
As I say, just personal musings. I find it quite interesting.