Travelling - I'm absolutely convinced all of this stuff is related, and is genetic. I'm one of 6 siblings, and not only do all my 3 DC have developmental problems, all of my siblings have children with developmental problems.
I know DD is GSTM1 absent, and I presume all my nieces and nephews are as well. The significance of this is that all of their problems (I believe) is due to a digestive problem. (Caused or exasperated by being GSTM1 absent)
So gluten and dairy are not digested properly, which leaves peptides in the blood stream, which causes developmental problems.
But also vaccines aren't properly flushed out and residues from the stuff that contains the vaccine are left in the body which gets into the blood stream and causes developmental problems.
So if I had another baby (which I most certainly won't!) I would not give her any vaccinations and I'd keep her gluten / dairy free for a long time.
I know all my 3 were vaccine damaged. DS1 was properly scarily damaged. He went blind and developed nystagmus and regressed the day of his 3 month DTaP vaccination. (He regained his sight about 6 months later, but he still has some nystagmus)
No health professional doubts that he was vaccine damaged.
So we didn't get DD and DS2 vaccinated. But the HV kept going on and on and on about it. And I didn't know then what I know now. So when they were 2 and 3 (they're a year apart) DH got them vaccinated.
And that is when their problems started. They didn't regress, but they stopped developing normally.
For example DDs word finding problems started then. Her speech was absolutely fine till she had her vaccination, and then she couldn't learn new words.
For example, In Y4 I asked her what she did in Maths and she said 'a line and a dot and a dot' - she had a 3 year old vocab at 8.
So there's no way I'd give a baby related to me vaccinations or gluten or dairy unless somehow I'd proved they didn't have a digestive problem. I'm not exactly sure how you could prove that.