When you want to move any of your muscles, your brain sends a signal through your nervous system to your muscles. With SMA, that message stops either completely at the spinal cord, or is sent only partially through. "Spinal" in SMA comes from that. When the muscles don't get any notifications to move, they lose strength, or atrophy, over time from lack of use. Hence "muscular atrophy".
SMA is hereditary, but only recessively. That means the gene has to come from both parents, but neither of them may actually have SMA. The amount of changes in the gene compared to a normal gene affects the level of the actual disability, meaning fewer changes mean less disabled person. Usually SMA is divided into three different types based on the level of disability, but there are also a few other muscular disorders with same kind of symptoms. SMA is found all over the world, so ethnic background or bloodtype don't affect the chances of having a child with it. Every year a few children are born with SMA in Finland.
There is no treatment available for SMA. There are however some forms of therapy and special medical equipment in use, which help improve the SMA-person's quality of life. The person's disability won't get better, but these methods will slow down the atrophy process considerably. Too much exercise can as a matter of a fact make things worse, and make a muscle stop responding completely.
SMA II, the type I have
This is the intermediate form of SMA. According to some doctor, the ability to sit on your own at some point of your life means type II. Those with type I can't even do this, and with type III you have been able to stand or even walk without support. If you can sit on your own at the age of 13, you can keep that skill for the rest of your life. SMA II doesn't really progress anyway. Aging can make some muscles a bit weaker, though. Sometimes a single nerve can stop relying the message due to over-use or some other unknown reason. One of my fingers stopped working correctly some years ago. One minute I was able to push buttons with it and keep it bent, the next minute it was impossible. It hasn't got any better, so I've learned to do those things in other ways.
Only the voluntary muscles are affected by SMA II, and the same goes for other types. The heart, the lining of the oesophagus (stomach and so on) and diaphragm for example aren't affected at all or very little. The bigger the muscle the more it's affected by SMA. For example, I basically can't lift my arm from the shoulder at all, but my fingers still work properly. Back muscles also are weaker than normal, and this causes scoliosis, spine curvature. Usually this can be fixed to a certain point by attaching metal bars to the spine to keep it straight(er). There are a lot of different types of bars and attaching methods being used. I have two metal bars on my spine, and they go from my neck almost to my tail bone. I sit a lot straighter than without them, but still not totally straight. The brain isn't a muscle, by the way, so just like any other muscular disorder, SMA doesn't affect it at all. One doctor actually said once that people with SMA tend to be more clever than average. ;-)
I use an electronic wheelchair ("power chair") to get around. I have a "normal", pneumatic wheelchair as well, but I use it mainly on trips and other inaccessible places. My electronic wheelchair is too heavy to be lifted and even one real step is too much for it. I live basically on my own in a rental apartment. My personal assistants (not care-takers, since they don't have to take care of me) help me to do things I'm otherwise physically unable to do, like getting a book from a shelf or cooking. I can use a computer by myself and do other small things, which don't require reaching or lifting. I've always attended the same schools as everyone else in my neighbourhood. In class I'm just like other students, even though I can't raise my hand properly. In short, I can read, write, talk and think by myself. Can you?