Are people on the spectrum "born into" different brains?

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... or are their brains the exact same as neurotypicals, but with a slightly different brain structure (localized brain damage leading to executive dysfunction, more synapses etc.), but with all other brain structures completely intact?

Just curious really.

There are some good texts about this topic, including "The Neuroscience of Autism Spectrum Disorders" by Buxbaum and Hof, which I read cover-to-cover to better understand my autism. The differences seem to become pronounced around two years of age, rather than at birth. It turns out that there is some variation across types and severity of autistic conditions, but generally those with autism spectrum disorders have systemic and global differences in neuroanatomy. For instance at the smallest level the microtubule structure and the layering of cells on the outer cortical surface differs in those with autism. On a larger anatomical scale there tends to be greater short-range axonal connections and fewer long-range connections than with neurotypicals due to abnormalities in pruning of axons and the rate of brain tissue growth (which is the inverse of the case with schizophrenia) - this seems to produce tight loops of fast neural processing and some reduction of integration between brain nuclei that are far apart. I'd bet that's why language processing is affected in ASDs - lots of cognitive activity happens but it's not well integrated with the speech center. And I'd also bet that this reduced integration is responsible for increased alexithymia and poor executive function in autistics. Still over time autistics form new connections through the neuroplastic formation of new tissue - Temple Grandin writes about this and actually has fMRI images of her own brain showing the formation of long-range connections of new axons. In my case I have an injury to the corpus callosum producing a near split-brain condition and brain MRIs have shown neuroplastic tissue formed across the vein of Galen connecting the two hemispheres - when I was young I had a heck of a time using my left and right eyes together, hands together, etc. There are some autistic conditions that do result in specific localized damage through lesions as well...

Very informative.

We are "wired" differently yes. Was gonna mention the Temple Grandin story myself.

So, you're asking whether or not the alteration is over the entire brain, or just localised to a few areas?

Complicating matters is the fact that there isn't just one route to autism. Autism is determined by symptoms, not by brain scans. There may be several different brain alterations that lead to similar symptoms and are consequently filed under autism.

Also, autistic individuals apparently have increased neuroplasticity - our neurons form connections more easily. It would be interesting to see if people with "sub-clinical autism", having autistic traits but not the degree that would warrant a diagnosis, also show this, and whether it improves learning ability. That would explain how autism could be heritable but not down to de-novo mutations, and yet stay in the genome despite severely impacting reproductive success - if autistic traits improve fitness up to a point, then the carriers would pass on the genes, similar to sickle cell anemia in west Africans.

My mother said, she felt me methodically examining my surroundings before I was born... I don't know if the word "autism" is right here, I don't even have a "proper" diagnosis. Learned to talk faster than norm (complex sentences at 18 months), so nobody was worried, I was just "weird and hysterical, with strong attraction to sciences".
And there is some evidence that my hardwired weirdness started before I was born.