I'm not a medical professional, but as a PD patient, I share your situation. I, my brother, and my late Father had ET throughout our Teen and Young Adult lives. My Father was diagnosed with PD at age 75, and my PD diagnosis came at age 44. My brother, now 70, is re-visiting his ET diagnosis because his physician thinks he may have PD. So I guess our little TWO-person case study points to the possibility that ET may morph into Parkinson's, although I've yet to find confirmation of that from the medical community.