The disease usually starts in the 30s and 40s, but about 10 percent of HD cases have their onset before age 20 (juvenile HD).
[bcm.edu]
[…] before the age of 20, less frequently when onset is between ages 20 and 40, and rarely with onset above the age of 40. 18 Seizures in DRPLA can be tonic, clonic, tonic-clonic
[jnnp.bmj.com]
In contrast, adult HD usually presents with the gradual onset of clumsiness, chorea and cognitive and behavioral changes.
[bcm.edu]