Autism is a disorder that I find quite intriguing, though I think I'm more interested in what is wrong rather than how things gets broken in the first place. It's part of a spectrum of disorders, I'm sure everyone's heard of Aspergers syndrome, a less severe psychological condition on the same spectrum - a lot of geeky people can to a limited degree, identify with some of the associated traits which I suspect leads to a significant amount of self-mis-diagnosis.
We don't know what causes autism, or even exactly what is going wrong in the brain. Some people who are willing to discount all the evidence to the contrary claim it's vaccines, but it takes a significant amount of wilful blindness to believe that these days. This study doesn't identify a cause. It does however give us a clue as to what might be wrong. It's done on a very small sample size, which is understandable - it's looking at neuron concentrations in certain regions of the brain, which means that you have to wait until people die (making it quite a sad research project as well). Basically though, there are increased concentrations of neurons in a part of the brain that deals with language, social development and emotions. When our body develops, there's actually quite a lot of cells dying. For example, we don't grow fingers, we grow a paddle and the cells between our fingers then die off. When our brains are developing, there's something similar happening. There are a bunch of neurons that are used as a scaffold for other parts of the brain, which are then meant to die off. If these aren't dying then they could be contributing to the excessive neuron density and thus preventing the all of the neurons that would normally be there from integrating properly.