A year after co-founding his law firm in 1996, Steven Yankelevitz learned he had Parkinson’s disease. But he was determined not to let it affect his 10-hour workdays.

“It wasn’t one of my better moments,” said Yankelevitz, a partner in the L.A.-based Liner Yankelevitz Sunshine & Regenstreif. “But I knew I wasn’t going to quit or get on disability.”