My grandson had genetic testing done.... he has a tremor, and with his other challenges (global developmental delay, Sensory Processing Disorder), they wanted to make sure there wasn't a genetic basis for these conditions.
There were a couple of minor things they noted (I don't remember what), but nothing that would account for his conditions. They were looking for something more like Fragile X syndrome or something like that.
He is 7, and was 3 or 4 when it was done.
My brother (now 66) had it done probably 8 (?) years ago... he was having early memory issues, and they found the MTHFR issue. The doctor put him on some specific vitamin supplements to counteract the lack of B vitamin processing, but it didn't really help. He has had some major cognitive issues already, and had to take an early retirement.