When my sister called today to say we were right and her son does have SPD, my first thought was, "What?!"--I misheard "STDs." (The kid isn't even one yet!).
SPD is Sensory Processing Disorder. With SPD, a person (usually a child, and usually a boy) either gets too much or too little feedback from their senses, processing the sensory input "wrong" and leading to sometimes bizarre behavior to either get more or avoid sensory input.
SPD happens in all the senses, and not evenly. Where one sense might be hypersensitive, another might be undersensitive, leading a kid to run constantly or speak too loudly but refuse to eat most foods and wear most clothes. The "broken" sensory input can come in from any of the "standard" (taught in elementary school) five senses: taste, touch, smell, sight, or hearing; or from the "other" senses, which have big names that are actually more confusing but which are, in essence, the sense of where your body is in space (movement, balance) and the sense of where your body is in relationship to itself (where your limbs are, what angle your joints are bent at, is your head tipped to one side, etc). I suspect there are other senses that aren't on the standard SPD list, like pain. Pain is a sense--it's not touch or taste or smell or sight or hearing; it's not you-in-space or your-body-connected. And yes, it interacts with the other senses, but so do smell and taste, and sight and hearing, and touch and taste.
SPD is normally diagnosed in boys and is not considered genetic. It is often associated with autism because ALL autistic children have SPD, but in reality, not all children with SPD have autism (like all bipolar people sometimes are depressed, but not all depressed people are bipolar). SPD is also extremely common among profoundly gifted people (and some people theorize is related to their intelligence: they take in and process more information than "average" people). One theory out there is that profoundly gifted people are often diagnosed with Asperger's or HFAutism because they actually have SPD and the disorders get confused with one another often. (Aspies, for example, don't like to be touched without warning. Neither do people with SPD, but that doesn't necessarily make them Aspies.)
SPD is newly on the radar--so much so that doctors and psychologists won't touch it, and many don't believe it exists. It has to be diagnosed by an occupational or physical therapist, and those are the people who most effectively treat it.
The "newness" of SPD is one reason I think people don't think it's genetic. There's not enough data to go around. Plus, it would be hard to collect data because it would necessarily be self-reported, and adults who have "always been this way" would not necessarily realize that not everyone was processing the world the same way they are, especially if they grew up and adapted and became fully functional adults. (Like that old question, what if I see blue the same way you see red--there would be no way to tell because the label is stuck to the color as you see it, not as everyone necessarily sees it. "Normal" is what you've always experienced and can function in--not necessarily what everyone is experiencing).
I, personally, DO think it's genetic. Why?
Because I'm pretty sure my kids have it, my sisters kids have now been diagnosed, and, as I got reacquainted with dozens of my maternal cousins this summer, I discovered that MANY of their children have it, too. Many of them, from different families.
The thing that struck me when I got home from one of these encounters where we all went, "Oh, your kid, too? How bizarre that we each have one or two kids like this...." is that this is also the family that has huge numbers of women with fibromyalgia.
Fibro runs STRONGLY in my family. Almost shockingly so.
Then I started thinking: Fibro is a disorder where your senses collect information and then process it "wrong", turning normal sensation into pain. Nobody knows what causes it, but everyone agrees that fibro is heavily influenced by hormones.
So my theory is that fibro and SPD are the same thing, but that fibro is processed through female hormones (that's why you see it primarily in women) and SPD is processed through male hormones (which is why you see it mostly in boys). Either way, your body's senses are processing information in a "wrong" way (primarily through hypersensitivity in fibro) and you are forced to adapt or medicate to survive.
I wish I had the time, resources, and expertise to test this theory. It would be a big deal to the world of SPD and fibro, opening doors of looking at things in new ways that hopefully would add insight that could lead to treatment. It certainly would be a groundbreaking study in both the SPD and fibro worlds! We certainly have a big enough family to actually do a legit genetic study--it's my mom's family, and she was one of 7 children (each of whom had 3 or more children, and most of those children had 3 or more children) and has over a hundred first cousins. There are well over 300 people in my generation in this family--just first and second cousins--and almost all of those 300 had 3 or more children. I wish I could get them all together, explain SPD and Fibro (both of which often go undiagnosed, so I'd have to explain it all in detail), and say, "How many of us have kids like this? How many have fibro? Can we trace the genetics somehow?"