I believe I can help you with your concern
I am so sorry that your son has been exhibiting these symptom, may I ask for how long has been behaving in this way?
Also how does your son do in school with his studies, is he considered a good student academically?
And you mentioned that you thought is was Asperger's Disorder or an Autism Spectrum Disorder, but you felt that he did not exhibit other symptoms besides the lack of interaction with others, is that correct?
And he displays good eye contact when talking to others?
Does your son like to follow rituals or routines very often? Does he get upset at change at all?
Okay well he does not have OCD, a personality disorder, or a mood disorder because these symptoms have been present since he was 6 months old that you noticed. This signifies that this is a developmental disorder. Now you were great to look at the symptoms of Asperger's Disorder, but actually since last May that got removed from the Diagnostic and Statistical manual of Mental Disorder 5th edition (DSM-5) and instead got lumped in with Autism Spectrum Disorder (299.00) which your son meets the criteria for.
Here is a link explaining it in more detail for you
Basically he meets the criteria for all 3 of the A category and meets the insistence on sameness and hyporeactivity in the B category, and then qualifies for the C, D, and E categories too
Well it is a new criteria and most psychologists, psychiatrists, and therapists are not required to use the DSM-5 criteria until I believe the start of 2015. So you would have to ask a psychologist or psychiatrist if they would be willing to use the new DSM-5 criteria to properly diagnose your son
But this is definitely a developmental disorder and also I believe it is in the mild range too, so I think good Cognitive Behavioral Therapy (CBT) treatment will help your son immensely.
Well just like any scientific practice, the psychological community updates the diagnoses based on current research. So the psychological and psychiatric community chose to remove Asperger's Disorder, so it is not longer a disorder, and instead group it with this other disorder called Autism Spectrum Disorder, which has significantly different criteria then Asperger's Disorder. So while your son does not meet the criteria for Asperger's Disorder he does meet the criteria for this new diagnosis of Autism Spectrum Disorder
That is why. It is like back in World War 2, where we called individuals that suffered psychological trauma that they had a diagnosis of "shell shocked," but now we use the term PTSD, with different criteria.
Well CBT should help him to learn to better express his positive emotions and to manage his negative emotions
CBT works by helping your son re-train his brain in a way to help him acknowledge positive emotions and to act in a socially appropriate manner (e.g. show excitement) and CBT will also help him manage his negative emotions and learn to express them in an assertive manner that is also appropriate. In addition. CBT has a premise that your negative symptoms are caused by negative thoughts, so if we change your thought process to be more positive and objective as well, then your negative symptoms will lessen.