Why is my son not responding to any stimulus although he seems OK?

Question

I have a son. His name if Fadil. He is 21 months young.

His main problem is: Fadil doesn't respond to any visuals. He can listen to the sound but doesn't know how to interpret them. 
We checked with eye specialist and he said anatomically everything is fine.

Now we are seeing a child neurologist. We did MIR and other boold test. Everything seems fine. Now he is getting some vitamins to speed up the development. 
At this stage, all he can do is roll his body. He doesn't want to sit. He can sit for some time but we got to hold him.

He is undergoing physio therapy and sensory integration therapy but the results are slow. Does unfortunately has come across any case like Fadil( my son)? What would you advise? 

I did his medical checkup in one of the best hospitals in Singapore and they couldn't comeup with any diagnosis. 

I appreciate any advise.

Firdous
A Father!!!

Answer 1

It sounds like it could be autism - a behavior pattern recognized in the US, but not recognized in many countries since the condition lacks a clear definition and cause.