ADHD and Parkinson's

I have a husband with Parkinson’s and a 20 year old son with similar executive function issues but no symptoms of Parkinson’s. Both also have extremely poor sense of smell and problems with constipation.  I keep looking for some connection that would explain both of their issues

My husband was diagnosed in 2008 with Atypical Parkinson’s/Lewy Body Dementia (both started at about the same time but the physical issues are progressing faster than the mental).  There is a study in which 48% of people with LBD had symptoms of ADHD in their youth, compared to 15% of the control and 15% of the group with Alzheimer's.  This is an issue I am interested in as the transition from my husband’s lifelong cognitive pattern, which we understood as a variant of Attention Deficit Disorder, to Atypical Parkinson's was so gradual and so much just more of the same.  Now it is further complicated because my husband's diagnosis was changed in 2012 from Lewy Body Dementia to Multiple System Atrophy, a different form of Atypical Parkinson's.

Our son has similar ADHD with particularly significant executive function issues and shows so much the same pattern as my husband.  Dr. Kenneth Bergmann originally evaluated John at Medical University of South Carolina. He looked at John’s initial neuropsych report and said “that’s not normal, that’s not even normal Parkinson’s” to have a verbal IQ 37 points higher than performance IQ. He saw that as one of several clear signs that John was on the path to Lewy Body Dementia.  But a year later our son Paul had a learning disability evaluation before he started college, and his verbal IQ tested 26 points higher than his performance IQ.  We kept saying that to Dr. Bergman  (who has since moved away to Washington) and he kept saying that it was just that John must have had mild DLB symptoms going back many years. That’s the standard answer I get from researchers on DLB. But it doesn’t fit my experience--John has always been this way, it just got worse.

I have found two genetic illnesses that involve ADHD when young and Parkinson's when older--subclinical Fragile X and Gaucher's disease carriers.  Fragile X would not link father and son and my son has been tested and does not have a high number of repeats.  My husband has been tested and does not have the most common genetic defect leading to Gaucher's, but there is research showing its link to Parkinson's and LBD.