Vivek's company Axovant Gene Therapies owned a drug called Intepirdine which failed to pass Phase 2 clinical trials. His solution was to redo the trials, but this time they were conducted by his mother Geetha. Incredibly, the trials demonstrated significant improvements from the last ones, enough to move on to Phase 3. At this point, he took his company public for a $315 million IPO in 2015, the largest of any biotech company in history. When the drug moved onto phase 3 trials that were not conducted by his mother, they failed, and the company lost 75% of its value in a single day. Luckily for Vivek, however, he had already sold tens of millions of dollars in his shares of the company, and so the losses didn't hurt his wallet.
Newsweek report on the subject
Wikipedia entry on the subject