Hi, sorry to have not responded in a while - especially since I started this discussion. I just came back and am trying to catch up. I don't want to seem pushy, but it seems to me there's a lot of misinformation mixed in with the real stuff. For start, "genetics" comes straight from both parents. 99.9% of genetic material is exactly inherited. The only way genetics could be "non-familial" is if you are the one the mutation occurred in for the very first time ever (so that no one else in your family had it). That's extremely rare, tho possible. And you would then be the one to pass on a whole new line of EM victims.
Veerla's referenced article is indeed not about the best known sodium channel mutation, Nav1.7 (gene SCN9A). It IS, though, still about another sodium channel also on peripheral nerves, Nav1,8 (I think that's gene SCN10A).
These two, and about 7 or 8 other genes, are ALL responsible for forming Nav sodium channels in the new fetus. Nav stands for: Na is the chemical symbol for the sodium atom, v stands for voltage gated channel.
Nerves do not have "pain switches" like little buttons. Nerves do a lot of different things. Pain nerves send electrical potential signals to the brain, where they are INTERPRETED as pain, say in the foot. The way these signals travel up the nerve fiber (axon, like its tail) from foot to spine, where the signal is transferred to another nerve) is because Sodium (Na) channels, little gates all along the length of the nerve fiber, open and close to let sodium atoms into the cell. Sodium, like many atoms, has one too many electrons, so it has a negative electrical charge. This allows the inside of the cell to build up a negative potential. The sodium channels all along the nerve open not all at once but in sequence down the line, so the electrical negative potential runs down the nerve. This IS the signal in a nerve. When it gets to the next nerve, the electrical potential is passed on, till it gets to the brain, where (even tho it feels that the pain is in the foot) the pain is actually noticed.
With a mutation of a gene for a sodium channel, the channels function improperly. Usually, according to research, the sodium channels along the nerve are opening too fast and staying open too long, so that the signals are "too much". That results in excess pain, if its a pain (sensory nociceptive) nerve. If its an autonomic nerve that tells the muscles around blood vessels in, say the foot to constrict or dialate, then that function is over-done instead.
And over time, research is thinking, excess firing of nerves due to too much sodium inflow, due to genetic mutations of sodium channels, deteriorates the nerves themselves. The nerve fibers can die back. This is small fiber neuropathy.
EM can be caused by mutation (and a sodium channel mutation means ALL sodium channels in your body that are designed by that specific gene are defective) or nerves can die back from toxin or disease or chemo or a lot of other reasons.\
Or a person can have non-genetic malfunctions, meaning though their genetic (blueprint) material is normal, their personal information gets misread as their bodies develop as infants. The meds that work on sodium channels to slow their actions (which I think is the Zenon drug) might not work on all EM, since the causes may be elsewhere. I can't say.
I know I've rattled on. Sorry if I'm out of line. It just seemed that there is a lot of confusion. I'm no expert. When I was diagnosed, I went to the bookstore and bought a college neurology book and first learned how the nervous system works. (Turns out voltage-gated channels, like sodium or potassium, are on the ground floor of the system). Then I went to the research. It becomes clearer that way.
I hope we all are relieved thanks to research, very very soon.