I don't know that they have really been able to correlate severity of symptoms with certain mutations except in a few cases. For example there are some mutations that only seem to cause symptoms during pregnancy.
It's possible your doctor just said you have a mild case based on the severity of symptoms you presented with that day, and was unaware that they could fluctuate.
Let´s se what the future hold.. If they will be able to point out severity, kinds of manifestation to some mutations and maybe target the mc with right medications and so on.....
I will ask my neurologist next time I see him what mutation i have :-)