I spent the last semester working with children who have autism. During this time, I heard the term "sensory issue" a bunch of times, but had no clue what it really meant. Even after asking questions about it, I never felt like I really understood it.
I ended up learning the most about sensory integration issues at an unsuspecting event - at a writer's conference in NYC. There, I so happen to have met Nancy Peske, the co-author of the book, Raising a Sensory Smart Child, and a mother of a child with the conceptually elusive sensory integration issue. I figured she'd be the perfect person to ask about this stuff.
I ended up learning that some people are prone to either seek out intense stimulation or find even the most mild sensations aversive. For instance, some children have an extremely high tolerance for what would cause most of us pain. Conversely, the same child may find light tickling painful or aversive. Although many people with autism have these types of sensory integration issues, we also see this in people who don't happen to have autism.
Relevant to my past research, we find that children who engage in self-injury are more likely to have a high pain tolerance and engage in repetitive behaviors. While we previously thought that having a high pain tolerance was caused by repeated episodes of self-injury, I'm wondering if actually there is an underlying sensory integration issue here. [In fact, we're finding that the traditional tolerance theory is not supported.]
On top of that, we have been conceptualizing repetitive behaviors as a precursor to self-injury; however, now I'm thinking that perhaps they both emerge out of the same sensory integration issue that may have been present from before / soon after birth.
And speaking of birth, in Deliberto & Nock, 2008, we report that in utero complications are seen more in children who engage in self-injury than in controls. Like repetitive behaviors and in utero complications, these findings are also seen in people who have autism. Although these data are correlational, the relationship among in utero complications and repetitive behaviors, self-injury, and autism is worth considering in my opinion.
In short, I'd bet that both self-injury and some of the underlying commonalities between this behavior and autism are sensory integration issues relating to touch.