What causes developmental disabilities? No-one truly knows, because we don't all call these disabilities by the same names.
There are many names for the type of disabilities which are linked with developmental problems. When my son was three he was diagnosed as having developmental delay of a year, and also said to have "learning difficulties". At the time the last phrase meant little to me, and I found the idea of developmental delay a bit of an obvious statement as I had asked for my son to be assessed when I, and others, believed he may not be acting like other children his age.
My son then was assessed six months later and said to be eighteen months behind in his development. This suggested he had not developed at all during the intervening time, but the truth was he had developed, only not as much as everyone thought he should have done.
At ten years of age, a special needs teacher told me my son lacked two and three dimensional vision; he couldn't follow a line on a grid on a piece of paper. It was only then I realised there was a serious problem in his brain that was having a great effect on his learning. If he couldn't see what we could see how could he learn what we wished him to learn? Why hadn't the earlier experts discovered this? Why was his brain acting like that?
There were no answers for me. All I could do was try to understand what what happening at the practical world stage, and I did learn shortly afterwards that the dimensional problem is linked to a disability of mental spacial awareness. No wonder my son was so clumsy, and drew arms which had three equal parts to them! My son not only had learning difficulties but was also suffering from Dyspraxia.
But as I learned more about this particular form of mental disability, I realised there were other areas in which he still didn't seem to be developing. I wondered if he was autistic but no-one took this idea seriously.
It wasn't until he was sixteen and had left school that I managed to persuade the authorities to reassess him, and asked them to check for autism. I had been saying for years to both his doctor and his school that I believed he had autistic tendencies, but no-one wanted to delve any further. He had been diagnosed already; there was no need to recheck the diagnosis!
As it turns out, he is also autistic. This links very closely with the dyspraxia in my mind because autistic children have difficulty understanding the structure of social interaction and procedures. In other words, they have problems fitting social activities and language into a mental spacial structure in their heads.
This suggests to me that when we develop our spacial awareness and form mental structures of where we are in our immediate spacial surroundings, we use part of that section of brain (or sub-programme) to also work out where we are in the structure of society, and any group of which we are a part. How to interact with the group is based on spacial understanding of how everything locks into place, like a jig-saw, and if we have problems defining this mentally, then it will affect any other mental function which requires a basic structure to create it.
Language is also based on a spacial structure, and I know my son had to be taught how to form a sentence, using symbols, rather than letters. Once he had finally grasped this his teachers were able to modify that structure into the English language, and he understood sentences as he read, not just individual words.
Now he is quite a good reader, although his spelling is still poor. He also has problems putting his feelings into words, but I know he does have feelings. I remember he suddenly burst into heavy tears one night, and it was due to watching a hospital drama which had a boy being knocked over and dying. My son related to this situation for the first time and whilst it was hard to watch his tears, I was nevertheless glad he had learned how to put himself in someone else's place and understand that it could have happened to anyone, including himself. Before this, he was unable to comprehend this concept at all.
Today, he is still severely mentally disabled, although at first glance he looks normal. He has found himself a partner who loves and cares for him, and in this at least he trying to live a "normal" life.
Physically, my son is a normal adult, now in his 20s, but mentally, in many areas he is still far behind his peers.
As to why this happened, I still don't know, and don't suppose I ever will. The experts don't know either, although they will probably use statistical evidence to suggest it is was due to one thing or another.
We get on with life, no matter what the cause. We accept that these things can happen to any of us, and we do all we can, whatever the reason for these developmental delays.
Was it due to my getting drunk at the Christmas during the first trimester? Was it due to the fact I was working near a machine which required me to be very close to it so I could operate it properly, and the vibration and noise from the machine could be felt by my baby? Was it due to the fact my waters broke before he was engaged in my pelvis and so his birth was more prolonged that it would otherwise have been? Was it due to his needing oxygen immediately after he was born? Was it due to the injections that I allowed him to have, even though he was born prematurely? Was it due to a genetic problem that other family members may have, but not so severely?
I ask the latter question because once I knew he was Dyspraxic I went to a lecture on the subject and participated in a simple experiment, which showed I was also slightly dyspraxic, but not anywhere near the same level of my son. Perhaps there is a genetic aspect, but it can't explain why my son's disabilities are so profound.
By the way, what I find most surprising is that my son has learned how to play chess, a very spatially aware game, yet he still struggles to do some of the simplest of jig-saws, and is unable to mentally "see" an optical illusion.
The brain is a strange thing, and its variances are of such a wide range it is impossible to fully understand the nuances of difference from one brain to another.