At this point early diagnosis would probably only provide slight benefits if any but maybe it can lead to something therapeutic over the long haul
"Thirteen blood biomarkers, including three never previously linked to Parkinson’s disease, may help in diagnosing people sooner and scientists in better understanding the condition, according to a study based on data from nearly 400,000 people."
High IGF-1 is one of the biomarkers. I find this unsurprising.
There are some researchers that believe in many neurological diseases, over time the brain is over exposed to IGF-1 and develops a sort of IGF-1 / MTOR resistance, almost like insulin resistance in diabetes.
I wrote about it a bit in a previous reply to one of the NALL topics:
healthunlocked.com/cure-par...
it does seem very logical that this would be the case
Vitamin B12 Supplements May Help Slow Parkinson’s Progression, Study Finds
STUDY: “High Prevalence of Undiagnosed Insulin Resistance in Non-Diabetic Subjects with Parkinson’s Disease” 
Molecule Delivered in Small Fatty Vesicles May Be Potential Parkinson’s Therapy, Mouse Study Shows
My PCP finally agreed to run Cystatin and NFL blood biomarker tests for me. 
Bicycling Ability May be Unaffected by Freezing of Gait in Parkinson’s
