The KyXy host will run Rock 'n' Roll San Diego on May 31.
For the Johnstons, 26.2 miles is a way to bond as a family and battle a devastating disease.
The Masters division is as strong as ever.
The 5K will take place the day before the marathon and half marathon.
The 91-year-old became the second oldest marathon finisher in U.S. history and set a new age-group record.
Check out these great shots from America's Finest City!
Deksisa, Dibaba capture titles; Keflezighi leads hundreds under 1:30 mark.
Twenty-three-year-old Anna Corrigan runs 2:44:28 to win her debut marathon.