Perhaps my signature is confusing--as far as I know, I have NO genetic markers associated w/ PD, and neither do my family members dx'd w/ PD. Here's part of another post I wrote that may clarify:
Most people with PD *don't* have LRRK2 or GBA mutations, or any other mutations strongly linked to familial PD. My dad had PD, and my sister was recently diagnosed. That might suggest a genetic cause, but we've have also lived in similar environments, associated with somewhat higher risk. And the specifics of the disease were somewhat different for us--my dad was diagnosed in his late 60s, tremor dominate, relatively fast initial progression (very typical PD profile). My sister has no tremor, but debilitating postural instability, and gait issues. Symptoms starting ~55 y.o., undiagnosed for 4-5 years until she went to an MDS. I was diagnosed at 46, tremor dominate, very slow progression to date.
Although my dad never had genetic testing, and I don't believe my sister has had any testing yet, I would be very surprised if either had LRRK2 or GBA mutations.
Re: sub-categorizing. My guess is we're still quite a way from treatments tailored to specific PD subtypes, since research into what constitutes subtypes and and the different causes is still at an early stage.
I try not to focus much on why I (in particular) wound up w/ PD. First, because there's likely no clear answer or single cause. Second, because for me it's a little too close to a 'why me?' kind of question, and too much 'why me?' seems likely to lead to dark places.