Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a name for a whole group of brain development disorders. It is quite common: about one percent of the world population has it (with men being diagnosed 4-7 times as often as women). Apart from the -- obviously -- autistic disorder it includes Asperger’s (commonly known as milder, high-functioning autism) and pervasive developmental disorder (which is somewhere between Asperger’s and autism). All of these conditions are characterized by impaired social and communication abilities and repetitive/structured behavior and interests; the severity of particular impairments determines where on the spectrum the person will land. Someone might be silent and completely locked in some repetitive kind of activity for hours, while someone else would talk non-stop about their special interests, not take a clue about when to stop and completely miss irony or sarcasm.

What ASD does not automatically mean, however, is genius intelligence (sorry, Sheldon!). Level of cognitive functioning in autism ranges from profound disability to superior intelligence 1 . While the view that autism is generally associated with lower IQ is becoming a bit outdated (as scientists start to acknowledge that it might result from the common IQ tests not tapping the true cognitive ability of many autistic children), more recent studies show that almost half of the children with ASD had average or above average intelligence 2 . Also, to make everything a bit more complicated, a relatively new study published in Nature showed that genes linked with a greater risk of developing autism may also be associated with higher intelligence (also people who were carrying the genetic combination in question but didn’t have ASD scored better on cognitive tests) 3 .

ASD has no single known cause; generally, it is agreed that genetic components play a very important role 4, 5, 6 (autism tends to run in the family, identical twins are more likely to both have it than fraternal twins etc etc). Still, it is not clear, what exactly happens there: there is not one "autistic gene" but rather a complex bundle of interactions. However, another thing that is clear (and important for this blog post) is that at least some of the involved genes are responsible for the mishaps in the ASD brain development.

Autistic Brain

There are quite some aspects in which autistic brains differ from the “neurotypical” ones. First of all, children with ASD generally have bigger brains. 7, 8, 9 One of the possible reasons is the larger amount of white matter as compared to non-autistic people. In the period between 6 and 14 months children normally undergo a phase of rapid synapse (=connection between nerve cells) growth which is then followed by a process called “pruning” where unnecessary connections are eliminated. It is thought that pruning doesn’t go as planned for children with ASD leaving them with an unusually large number of synapses that are in the way of efficient information transfer. One study has examined brains of autistic children of different ages (who died of some unrelated causes) and found that by the late childhood, the number of synapses in their brains had dropped by only 16 percent, whereas in the control brains it dropped by about half 10 . They also found the possible cause behind it: a protein which is normally supposed to help the cells to, however harsh it might sound, destruct some of their parts (=autophagy) was defective. It resulted in these excess synapses and brain cells filled with old and damaged parts which couldn’t have been disposed properly. The scientists managed to restore normal autophagy and pruning and reverse autistic-like behaviour in mice by giving them a drug that made this defective protein function normally again.

Another factor which might contribute to the larger brain size is the number of neurons in the prefrontal cortex, the brain area responsible for complex stuff like reasoning, communicating, managing social interactions etc. It was found that autistic boys have 67 percent more neurons in their prefrontal cortex (and 17 percent heavier brains) than their non-autistic peers 11 . Quantity does not equal quality in this case, however: it means a huge increase in potential connections and thus a potential for faulty wiring between brain cells. It is also interesting to say that the prefrontal cortex neurons are born during pregnancy meaning that autism starts as early as in the womb. This paves the way to understanding the exact molecular mechanisms behind the abundant neuron production and possibly -- let a girl dream a bit -- developing treatments counteracting it.