I was tested for mutations to all the genes that can cause HSP and are recessive by Athena Labs. (My parents didn't have symptoms, so it was reasoned it wasn't dominant.) SPG7 is in charge of making the mitochondria that recycle misfolded proteins in your cells. The mutation I have hasn't been seen in anyone else tested so far, and my mom doesn't share it, so it is "de novo" - I'm a first generation mutant. Progression-wise, I am more of a PLSer than an HSPer, but I have the complications that HSP brings. So if another person shows up with my particular mutation and symptoms that match, they'll have to decide whether to label this a PLS or HSP causing mutation. And I never mind sharing.