The restructuring enacted by Sarepta Therapeutics is expected to save up to $400 million in annual costs. Read why I'm downgrading SRPT stock from Hold to Sell.

Sarepta (NASDAQ:SRPT) has now seen a third fatal incident in its gene therapy trials due to acute liver failure. That happened last month in a limb girdle muscular dystrophy study and follows two teenage deaths in advanced Duchenne muscular dystrophy patients.

As mothers of children with this disease, we have wept helplessly in recent months as friends — fellow members of a club we never asked to join — said goodbye to their sons, the babies they once held in their arms, whose dreams they held in their hearts until Duchenne robbed them of working muscles or a healthy future.

The drop comes the day after the drugmaker said it would add a so-called black-box warning to its gene therapy Elevidys after two teenage boys receiving the treatment died earlier this year.

Three patients with a muscle-wasting disease died from liver failure after taking the therapy, Ele­vidys, or a similar treatment.

CNBC's Angelica Peebles joins 'Squawk on the Street' with the latest news on Sarepta following a patient death.

Stocks traded mixed Friday as investors focused on corporate earnings, a day after the S&P 500 and Nasdaq Composite set record closing highs.These stocks were making moves Friday:Second-quarter profit at Netflix rose 46% to $3.

Stocks on Sky High. Sarepta Therapeutics, Inc. (NASDAQ:SRPT) is one of the top-performing companies on Thursday. Sarepta Therapeutics saw its share prices rise by 19.53 percent on Thursday to close at $21.