It is explained as being a disorder of a neurobiological nature.
Looking for information about it usually describes the same story.

http://www.udel.edu/bkirby/asperger/aswhatisit.html
- Individuals with AS can exhibit a variety of characteristics and the disorder can range from mild to severe. Persons with AS show marked deficiencies in social skills, have difficulties with transitions or changes and prefer sameness. They often have obsessive routines and may be preoccupied with a particular subject of interest. They have a great deal of difficulty reading nonverbal cues (body language) and very often the individual with AS has difficulty determining proper body space. Often overly sensitive to sounds, tastes, smells, and sights, the person with AS may prefer soft clothing, certain foods, and be bothered by sounds or lights no one else seems to hear or see. It's important to remember that the person with AS perceives the world very differently. Therefore, many behaviors that seem odd or unusual are due to those neurological differences and not the result of intentional rudeness or bad behavior, and most certainly not the result of "improper parenting".

By definition, those with AS have a normal IQ and many individuals (although not all), exhibit exceptional skill or talent in a specific area. Because of their high degree of functionality and their naiveté, those with AS are often viewed as eccentric or odd and can easily become victims of teasing and bullying. While language development seems, on the surface, normal, individuals with AS often have deficits in pragmatics and prosody. Vocabularies may be extraordinarily rich and some children sound like "little professors." However, persons with AS can be extremely literal and have difficulty using language in a social context.

At this time there is a great deal of debate as to exactly where AS fits. It is presently described as an autism spectrum disorder and Uta Frith, in her book AUTISM AND ASPERGER'S SYNDROME, described AS individuals as "having a dash of Autism". Some professionals feel that AS is the same as High Functioning Autism, while others feel that it is better described as a Nonverbal Learning Disability. AS shares many of the characteristics of PDD-NOS (Pervasive Developmental Disorder; Not otherwise specified), HFA, and NLD and because it was virtually unknown until a few years ago, many individuals either received an incorrect diagnosis or remained undiagnosed. For example, it is not at all uncommon for a child who was initially diagnosed with ADD or ADHD be re-diagnosed with AS. In addition, some individuals who were originally diagnosed with HFA or PDD-NOS are now being given the AS diagnosis and many individuals have a dual diagnosis of Asperger Syndrome and High Functioning Autism. -


One question is, why is it, despite what is mentioned above: "Individuals with AS can exhibit a variety of characteristics", that as-people are often
correlated with INTP and also INTJ or close to that?

If these aspies are "wired" (=hardware) differently in their brains as they say themselves, are all INTP (or INTJ or..) "wired" differently too?!!
Wired in a certain way? Are all people wired in as much variation? Is an ESFJ wired differently than an ISFJ or do they only have different
"software"?
People defending As say it is inherited, genetically and not a product by the environment.

However, we must logically conclude that there are many
As-(mis)diagnosed people whos basic personality is entirely formed by circumstances in childhood and later.