After diagnosis - gene testing? CT scan?

Hi all, I’m a mum to a three year old boy who has been all but officially diagnosed with autism. To give a very brief outline: he has very little functional language, just a few learnt phrases and lots of echolalia, he also has very little receptive language and can only understand the most basic of instruction (put it in the bin, close the door, etc) and even that is hit and miss. He spins/jumps/climbs on me constantly, bites everything and anyone in sight (when over excited which is nearly always) and is prone to meltdowns (not particularly sensory overload rather he will get incredibly angry about something not going his way and I think because of his lack of speech and understanding , this exacerbates the problem). He also had a big obsession with wheels which has eased slightly but did last two years. Eye contact and responding to name were also not at all present but this has got a bit better, though he still doesn’t wave or point. Anyway! An educational psychologist has recommended he go a special pre school and she has said when we get the paediatrician appointment in a few wks time, we should expect autism diagnosis.

So, what I wonder is assuming he gets this diagnosis, will he be tested for possible cause? There are a few reasons I ask. One is because he had a few very bad smacks to the head at around 12-18 months. We lived in a tiled apartment and on a couple of occasions somehow water got on the floor, he was running (as he always did!) and slipped and hit the back of his head. I took him to a&e and they said as long as he didn’t black out or doesn’t throw up, I shouldn’t worry. But the slips were so bad and hard and a friend slipped a few months back and had a brain bleed but neither blacked out nor vomited. So I am concerned if he had a significant trauma which has possibly triggered autism and / or a learning disability because it’s not just the social side of things he falls behind on, he really struggles to learn anything language wise (ears have been tested and all good ok that front). He also had a traumatic birth.

The other thing I would like to know is if it is somehow genetic, because I have my own issues (severe OCD, extreme shyness) and my husband’s nephew has been diagnosed as autistic (though my husband shows no traits). We’ve just had a baby and so of course it’s on my mind whether she will be autistic, and i would also like another baby but my son needs a lot of attention and so I don’t feel it would be fair on him to have another child if there is significant risk they’d be autistic (ie genetic) because I wouldn’t have the time/resources to give them what they deserve. I adore my son and he is such a delight when playing but he is very hard work. If my daughter also goes down that path, then I think I would be spread to thinly for a third child. 

So, in summary, what are the chances they would look for evidence of brain injury (for his possible learning disability re language) or at genes? Is it standard procedure?