I have come to understand that primary EM has something to do with a genetic mutation and secondary means you have another condition that is effecting you or has yet to show itself and may be in the future.
I thought since only certain genetic mutations would cause EM that you should be able to get a genetic test so they can see if your code has those mutations. This would at least give me some more reassurance that there isn’t something else I need to worry about. If anyone has gotten a genetic test like this I would appreciate the info, thanks.
I went to Prof David Bennett at the John Radcliffe Hospital in Oxford. He has funding so the genetic test is free. At that time they were only aware of one mutation - at SCN9A gene affecting a sodium channel NaV1.7 . I gather they have since discovered new genes SCN 8 or 11 or something like that
I had extensive blood tests to check whether I have primary or secondary erythromelalgia but no genetic test. The blood tests indicated I have primary erythromelalgia.
Chiming in. By way of background, I am NOT a doctor. I do have an undergrad genetics degree.
There are several genes in the SCN family of genes that instruct your body on how to build several related proteins. Geneticist aren’t always creative so these genes are named SCN1A, SCN2A, … all the way up to SCN12A. The protein products form subunits (think of them as individual Legos blocks) that collectively build things you will see referenced in articles, “voltage gated Sodium ion channels.” There are different such channels in different parts of the body. In EM we mostly care about those in sensory nerves.
The most common genetic mutation correlated with EM is to the SCN9A gene. Some patients have been identified with mutations to other genes in the family, particularly SCN10A and SCN11A.
The inheritance pattern of EM with people with a positive test results (meaning they DO have a mutated gene) is “Autosomal Dominant” meaning that 50% of their parents, siblings, or children would be expected to have the same mutation and similar symptoms. So, often genetically caused EM can be inferred without a test just because several family members have similar symptoms.
A positive genetic test might cause doctors to stop running some tests for other causes. As to treatment, maybe patients with a confirmed mutation might find medications that block those sodium ion channels to be more effective for them. Those are medications such as lidocaine and mexiletine.